@database "VCR-Repair" @node main "VCR Repair" Notes on VCR Failure Diagnosis and Repair Contents: @{" Chapter 1 " link "1"} About the Author & Copyright @{" Chapter 2 " link "2"} Introduction @{" Chapter 3 " link "3"} Video Recording Technology @{" Chapter 4 " link "4"} VCR Placement, Preventive Maintenance, and Rental Tapes @{" Chapter 5 " link "5"} VCR Maintenance and Troubleshooting Guide @{" Chapter 6 " link "6"} VCR Tape Transport Fundamentals @{" Chapter 7 " link "7"} Cassette and Tape Loading Problems @{" Chapter 8 " link "8"} Fast Forward and Rewind Problems @{" Chapter 9 " link "9"} Play and Record Mechanical Problems @{" Chapter 10 " link "10"} General Control Problems @{" Chapter 11 " link "11"} Play and Record Control Problems @{" Chapter 12 " link "12"} Video Play and Record Problems @{" Chapter 13 " link "13"} Audio Problems @{" Chapter 14 " link "14"} Signal and Interference Problems @{" Chapter 15 " link "15"} General System Problems @{" Chapter 16 " link "16"} Miscellaneous Problems @{" Chapter 17 " link "17"} A Few Model Specific Problems @{" Chapter 18 " link "18"} Video Heads and Upper Cylinders @{" Chapter 19 " link "19"} Tape Path Alignment and Backtension Adjustment @{" Chapter 20 " link "20"} VCR Sensors and Tape Counters @{" Chapter 21 " link "21"} Motors and Rotors @{" Chapter 22 " link "22"} Items of Interest @{" Chapter 23 " link "23"} Service Information @endnode @node 2 "Chapter 2) Introduction" @{" 2.1 " link "2.1"} Entertainment - then and now @{" 2.2 " link "2.2"} VCR repair @{" 2.3 " link "2.3"} Repair or replace @endnode @node 3 "Chapter 3) Video Recording Technology" @{" 3.1 " link "3.1"} Helical scan video recording @{" 3.2 " link "3.2"} VHS video @{" 3.3 " link "3.3"} VHS audio @{" 3.4 " link "3.4"} VCR servo systems @{" 3.5 " link "3.5"} Video Special effects @{" 3.6 " link "3.6"} For more information on VCR technology @endnode @node 4 "Chapter 4) VCR Placement, Preventive Maintenance, and Rental Tapes" @{" 4.1 " link "4.1"} General VCR placement considerations @{" 4.2 " link "4.2"} Preventive maintenance (PM) @{" 4.3 " link "4.3"} Rental tape considerations @endnode @node 5 "Chapter 5) VCR Maintenance and Troubleshooting Guide" @{" 5.1 " link "5.1"} Safety @{" 5.2 " link "5.2"} Troubleshooting tips @{" 5.3 " link "5.3"} Test equipment @{" 5.4 " link "5.4"} Cassette cheaters @{" 5.5 " link "5.5"} Test tapes @{" 5.6 " link "5.6"} Getting inside a VCR @{" 5.7 " link "5.7"} Why does my VCR shut down or behave strangely when I remove the cover? @{" 5.8 " link "5.8"} Getting built up dust and dirt out of a VCR @{" 5.9 " link "5.9"} What to do if a tiny tiny part falls into the VCR @endnode @node 6 "Chapter 6) VCR Tape Transport Fundamentals" @{" 6.1 " link "6.1"} Parts of the tape transport in a VCR @{" 6.2 " link "6.2"} Most common problems @{" 6.3 " link "6.3"} General guide to VCR cleaning and rubber parts replacement @{" 6.4 " link "6.4"} Lubrication of a VCR @{" 6.5 " link "6.5"} Head demagnetizing @endnode @node 7 "Chapter 7) Cassette and Tape Loading Problems" @{" 7.1 " link "7.1"} Cassette loading and eject problems @{" 7.2 " link "7.2"} Ejecting a cassette from an uncooperative VCR @{" 7.3 " link "7.3"} VCR is confused - will not eject non-existent tape @endnode @node 8 "Chapter 8) Fast Forward and Rewind Problems" @{" 8.1 " link "8.1"} VCR will not fast forward and/or rewind @{" 8.2 " link "8.2"} VCR aborts fast forward or rewind @{" 8.3 " link "8.3"} Tape rewinders @endnode @node 9 "Chapter 9) Play and Record Mechanical Problems" @{" 9.1 " link "9.1"} VCR refuses to record @{" 9.2 " link "9.2"} VCR aborts play or record during startup or shortly thereafter @{" 9.3 " link "9.3"} VCR aborts play or record at random times or near end of tape @{" 9.4 " link "9.4"} VCR eats tapes @{" 9.5 " link "9.5"} Tape loop hanging from cassette when ejected after play or record @{" 9.6 " link "9.6"} Tape sticks to head drum @{" 9.7 " link "9.7"} Video head drum stops or slows during play or record @endnode @node 10 "Chapter 10) General Control Problems" @{" 10.1 " link "10.1"} VCR is alive but will not do anything @{" 10.2 " link "10.2"} Erratic behavior in various modes @{" 10.3 " link "10.3"} VCR mode (sensor) switches @{" 10.4 " link "10.4"} Mechanical relationships in VCRs @{" 10.5 " link "10.5"} VCR does not work after cassette was forcibly removed @{" 10.6 " link "10.6"} The VCR is failing the power-up sequence @{" 10.7 " link "10.7"} VCR displays DEW warning @{" 10.8 " link "10.8"} VCR shows LOCKED in the display @{" 10.9 " link "10.9"} VCRs with Alzheimer's Disease @{" 10.10 " link "10.10"} VCR has gone whacko @{" 10.11 " link "10.11"} VCR forgets settings following power failure @endnode @node 11 "Chapter 11) Play and Record Control Problems" @{" 11.1 " link "11.1"} VCR randomly switches speeds, tracking problems, and muddy sound @{" 11.2 " link "11.2"} VCR plays but at fast forward speed (or beyond) @{" 11.3 " link "11.3"} Tape edge gets creased and/or random switching between speeds @{" 11.4 " link "11.4"} Recording stops at random times on previously used tapes @{" 11.5 " link "11.5"} Record (or play) stops after 15 minutes (or 30 minutes, etc.) @endnode @node 12 "Chapter 12) Video Play and Record Problems" @{" 12.1 " link "12.1"} Video playback problems @{" 12.2 " link "12.2"} Video record problems @{" 12.3 " link "12.3"} Snow on one or more speeds @{" 12.4 " link "12.4"} Jumpy picture in play @{" 12.5 " link "12.5"} Incorrect frame alignment or bad video for part of frame @{" 12.6 " link "12.6"} Rainbow pattern in recordings made over previously recorded tapes @{" 12.7 " link "12.7"} Flag waving @endnode @node 13 "Chapter 13) Audio Problems" @{" 13.1 " link "13.1"} Poor quality sound on non-HiFi VCR @{" 13.2 " link "13.2"} Excessive flutter on VHS linear audio playback @{" 13.3 " link "13.3"} Previous (non-HiFi) audio is not erased on new recordings @{" 13.4 " link "13.4"} Poor quality sound on HiFi VCR @{" 13.5 " link "13.5"} Squealing noise from VCR in certain modes @{" 13.6 " link "13.6"} High pitched whine from inside VCR @endnode @node 14 "Chapter 14) Signal and Interference Problems" @{" 14.1 " link "14.1"} VCR color problems @{" 14.2 " link "14.2"} RF signal problems @{" 14.3 " link "14.3"} VCR will not tune broadcast or cable @{" 14.4 " link "14.4"} Interference as parallel horizontal lines when playing tape @{" 14.5 " link "14.5"} Firing (static) lines in picture during playback @endnode @node 15 "Chapter 15) General System Problems" @{" 15.1 " link "15.1"} Multiple system problems @{" 15.2 " link "15.2"} Power supply problems - unit totally dead/major system problems in all modes @{" 15.3 " link "15.3"} VCR power supplies @{" 15.4 " link "15.4"} Internal fuse blew during lightening storm (or elephant hit power pole) @{" 15.5 " link "15.5"} Use of surge suppressors and line filters @endnode @node 16 "Chapter 16) Miscellaneous Problems" @{" 16.1 " link "16.1"} VCR poops out after a couple of hours @{" 16.2 " link "16.2"} VCR was dropped @{" 16.3 " link "16.3"} VCR or camcorder went to the beach (sand and/or surf) @{" 16.4 " link "16.4"} Dead remote control units @{" 16.5 " link "16.5"} Recovering damaged or broken tapes @{" 16.6 " link "16.6"} Cassette rewinder problems @endnode @node 17 "Chapter 17) A Few Model Specific Problems" @{" 17.1 " link "17.1"} Dead Clock in Hitachi manufactured VCR @{" 17.2 " link "17.2"} JVC tracking problems and dropped parts @{" 17.3 " link "17.3"} Panasonic and clones switching power supplies @{" 17.4 " link "17.4"} Late model Sony VCR munches tape on eject @{" 17.5 " link "17.5"} Symphonic/Funai brand vcr won't rewind or fast forward @endnode @node 18 "Chapter 18) Video Heads and Upper Cylinders" @{" 18.1 " link "18.1"} What is a Video head? @{" 18.2 " link "18.2"} Are your videos heads really bad? @{" 18.3 " link "18.3"} Need for video head cleaning @{" 18.4 " link "18.4"} Video head cleaning technique @{" 18.5 " link "18.5"} Advanced video head testing techniques @{" 18.6 " link "18.6"} Where to obtain replacement video heads @{" 18.7 " link "18.7"} Video head replacement technique @{" 18.8 " link "18.8"} Can I substitute a video head from another VCR? @endnode @node 19 "Chapter 19) Tape Path Alignment and Backtension Adjustment" @{" 19.1 " link "19.1"} General tape path alignment problems @{" 19.2 " link "19.2"} Adjustment of A/C head - problems with tracking or sound (linear audio) @{" 19.3 " link "19.3"} Roller guide height adjustment @{" 19.4 " link "19.4"} Likely causes for sudden change in tracking behavior @{" 19.5 " link "19.5"} Backtension adjustment @endnode @node 20 "Chapter 20) VCR Sensors and Tape Counters" @{" 20.1 " link "20.1"} Tape start/end sensors @{" 20.2 " link "20.2"} Start/end sensor testing @{" 20.3 " link "20.3"} Tape counters @{" 20.4 " link "20.4"} Reel rotation sensors @{" 20.5 " link "20.5"} Reel rotation sensor testing @endnode @node 21 "Chapter 21) Motors and Rotors" @{" 21.1 " link "21.1"} Types of motors in VCRs @{" 21.2 " link "21.2"} Repairing small motors @{" 21.3 " link "21.3"} Capstan problems @endnode @node 22 "Chapter 22) Items of Interest" @{" 22.1 " link "22.1"} Why is a tracking control needed @{" 22.2 " link "22.2"} Old clunkers and the march of technology @{" 22.3 " link "22.3"} Can I add an S-Video input to my VCR? @{" 22.4 " link "22.4"} Can a VHS VCR record single video frames at a time? @{" 22.5 " link "22.5"} Why is a special VCR needed for multiple video standards? @{" 22.6 " link "22.6"} What is a delay line and where is it used? @{" 22.7 " link "22.7"} Why are there so many different design for VHS transports? @{" 22.8 " link "22.8"} Service center honesty? @{" 22.9 " link "22.9"} IR detector circuit @{" 22.10 " link "22.10"} VHS specifications @{" 22.11 " link "22.11"} Luminance Specifications for various VCR technologies @endnode @node 23 "Chapter 23) Service Information" @{" 23.1 " link "23.1"} Advanced VCR troubleshooting @{" 23.2 " link "23.2"} FCC ID Numbers of VCRs @{" 23.3 " link "23.3"} Determining belt, tire, and pinch roller specifications @{" 23.4 " link "23.4"} Interchangeability of components @{" 23.5 " link "23.5"} Suggested Parts Suppliers @{" 23.6 " link "23.6"} Other Sources @endnode @node 1 "Chapter 1) About the Author & Copyright" Author: Samuel M. Goldwasser E-Mail: sam@stdavids.picker.com Corrections/suggestions: [Feedback Form] [mailto] Copyright (c) 1994, 1995, 1996 All Rights Reserved Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: 1. This notice is included in its entirety at the beginning. 2. There is no charge except to cover the costs of copying. This document converted to AmigaGuide format by Mike Fuller 27-7-96 ----------------------------------------------------------------------------- @endnode @node 2.1 "Entertainment - then and now" Think back 20 years. You went to the theater to see a movie. You watched TV programs when they were broadcast (there was no cable, remember?) or you missed them. TV studios and industry had video recording equipment but it was expensive and cumbersome. Little did you realize at the time, but after some false starts, the modern video revolution was about to be born. Are we better off? Whatever you decide, there is no going back. You may be able to leave your VCR's clock flashing 12:00 but you cannot escape the impact that this technology has had on so many aspects of your life. The video cassette recorder is a wonderful example of extremely complex precision technology that has been made affordable through mass production. In general, it is usually quite reliable. Treat a modern VCR with a bit of respect and it will provide trouble free service for a long time. Unlike a TV where the power circuits take their toll on circuit components, the electronics in VCR are generally quite reliable and rarely fail. Most VCR problems are mechanical - dirt and dust in the tape path, deteriorated rubber parts, dried lubrication, wear of precision parts including the spinning video heads, and abuse caused by rocks, toys, and peanut butter and jelly sandwiches. ----------------------------------------------------------------------------- @endnode @node 2.2 "VCR repair" Even if you are a technoklutz who lets your kids change the light bulbs in your house and would never consider tackling any actual repair or internal maintenance of your VCR, some basic awareness of the principles of video recording and the likely causes for common problems will enable you to intelligently deal with the service technician. You will be more likely to be able to recognize if you are being taken for a ride by a dishonest or just plain incompetent repair center. For example, did you know that one of the most dreaded of problems - the tape eating VCR - can often be remedied by a thorough cleaning and a 50 cent rubber tire? This document will provide you with the knowledge to deal with over 85% of the problems you are likely to encounter with your VCRs. It will enable you to diagnose problems and in most cases, correct them as well. First and foremost are the techniques for cleaning of the tape path and replacement of rubber parts like belts, tires, and the pinch roller - the solution to many common problems with VCRs. With minor exceptions, specific manufacturers and models will not be covered as there are so many variations that such a treatment would require a huge and very detailed text. Rather, the most common problems will be addressed and enough basic principles of operation will be provided to enable you to narrow the problem down and likely determine a course of action for repair. In many cases, you will be able to do what is required for a fraction of the cost that would be charged by a repair center. Should you still not be able to find a solution, you will have learned a great deal and be able to ask appropriate questions and supply relevant information if you decide to post to sci.electronics.repair. It will also be easier to do further research using a repair text such as the ones listed at the end of this document. In any case, you will have the satisfaction of knowing you did as much as you could before taking it in for professional repair. With your new-found knowledge, you will have the upper hand and will not easily be snowed by a dishonest or incompetent technician. ----------------------------------------------------------------------------- @endnode @node 2.3 "Repair or replace" While VCRs with new convenience features are constantly introduced, the basic function of playing a tape has not changed significantly in 20 years. Even the introduction of HQ about 10 years ago does not represent a dramatic improvement. Therefore, unless you really do need a quick start transport, a real time counter, index search, or the like, repair may not be a bad idea. The older VCRs are built much more solidly than the $150 models of today. Even high end VCRs may be built around a poorly designed transport and flimsy chassis. Many older VCRs - for example 10 year old Panasonic models (and their clones) can be kept functional - nearly indefinitely, it would seem - at minimal cost. If you need to send or take the VCR to a service center, the repair could easily exceed half the cost of a new VCR. Service centers may charge up to $50 or more for providing an initial estimate of repair costs but this will usually be credited toward the total cost of the repair (of course, they may just jack this up to compensate for their bench time). If you can do the repairs yourself, the equation changes dramatically as your parts costs will be 1/2 to 1/4 of what a professional will charge and of course your time is free. The educational aspects may also be appealing. You will learn a lot in the process. Thus, it may make sense to repair that old clunker so the kids will have their own VCR or you will have a convenient means of copying tapes (legally, of course). ----------------------------------------------------------------------------- @endnode @node 3.1 "Helical scan video recording" Modern VCRs - both consumer and professional - are based on what is known as helical scan recording. The main technological challenge that confronted the designers of early video recording machines was achieving the necessary bandwidth - several MHz - to faithfully capture the high frequency video signal. The first such machines ran normal audio tape past stationary recording heads at high speed - 10s of feet per second - in an attempt to solve this problem. Needless to say, the mechanisms were complex, a finite length of tape could only record a few minutes of video, and the heads wore out almost as quickly. If anything - anything at all - went wrong with the tape transport, you were up to your eyeballs is spilled tape. An alternative technology was clearly needed. Prior to practical video tape recording, the only way to preserve a TV show was to use special equipment that essentially made a film of it off of a video monitor. The quality of such recordings was not very good, editing was difficult, the film needed to be developed so playback was not immediate, and of course, the film could not be erased and reused. The first successful commercial video tape recorder was introduced around 1956 with the Ampex Quadplex - a $50,000 machine using 2 inch open reel tape and a high speed spinning head with 4 pickups rotating across the tape. This event revolutionized commercial broadcasting. However, this technology was much too complex, cumbersome, and expensive for consumer use and has a number of technological disadvantages as well. For a consumer video tape recorder to be successful it was felt that the following three major hurdles had to be overcome: o Tape loading had to be simple and foolproof using a cassette - none of this open reel stuff. o A cassette had to hold at least an hour of color video. o The cost to the consumer had to be less than $1000 (1970's dollars!) for the machine and perhaps $20 per hour for the tape. The rotating heads of the Quadplex machine provided the needed tape-head speed to achieve sufficient video bandwidth. However, the transport was much too complex for a consumer machine. Another disadvantage was that since a video frame consists of many adjacent tracks on the tape (16), special effects like stop motion as well as forward and reverse search were not possible without a frame store. While this would not be out of the question today, the cost of such a device in the 1950's would necessitate the consumer taking out a second mortgage to pay for it. Finally, the 2 inch wide format required too much tape for achieving a cost effective 1 hour program time and made the design of a manageable cassette an impossibility. A separate room would be needed to house a modest size video tape library! Helical scan overcomes most of these problems. Rather than scanning across the tape, the tape is wrapped a bit over 180 degrees around a rotating drum at a slight angle. Thus, successive tracks are written diagonally across the tape and can thus be much longer than the width of the tape as in the Quadplex. The tape, therefore can be rather narrow. The first helical scan tapes used a 1 inch format but narrower tape soon followed. The most common formats today are forms of VHS (and BETA) at 1/2", and 8 mm (mostly used for portable applications in camcorders and data storage.) 4 mm tape is used for high quality audio (DAT) as well as data storage. ----------------------------------------------------------------------------- @endnode @node 3.2 "VHS video" Most of the following discussion unless otherwise noted applies to the VHS format. Beta, which preceded VHS into the marketplace and which has all but disappeared for consumer VCRs is actually a somewhat better system technologically with superior picture quality. However, Sony's licensing practices with respect to BETA made it inevitable that VHS would triumph in the marketplace. Too bad in some ways. Each track corresponds to 1 field of the interlaced video format. Generally, two heads opposite each other on the rotating head drum are used. One rotation of the drum corresponds to a complete video frame with heads designated A and B for the even and odd fields respectively. What this also provides is the ability to easily implement a variety of special effects including freeze frame, and fully variable speed forward and reverse motion with a recognizable and in many cases, quite clear picture. With relatively minor restriction, this becomes as simple as moving the tape forward or backward or keeping it stationary. (Camcorders and other compact systems may use 2 pairs of identical heads where the opposing pairs are separated by 270 instead of 180 degrees. This permits the use of a smaller, lighter video drum.) The A and B heads are not identical either. Their azimith angle differs being +6 degrees for one and -6 degrees for the other. This is one of several techniques used to minimize crosstalk between adjacent tracks. Azimith angle is how far the head gap is from being perfectly perpendicular to the direction of tape-tape motion. For example, a head with an azimith such as / will ignore most of the information recorded with an azimith of \. Note that the head gap - the distance between pole pieces - is on the order of 1 um - 1/25,000 of an inch. As a point of reference, a human red blood cell is about 7 um in diameter and an average sheet of typing paper is about 100 um in thickness. The gap is filled with a nonmagnetic material to prevent it from getting clogged and to force the magnetic flux out of the head structure and into the tape magnetic coating. This remarkably fine spacing is necessary to achieve the multimegahertz video bandwidth. Actual tape motion for a VCR is remarkably slow. To someone familiar with audio decks, the tape in a VCR even at SP speed (the fastest) seems to be crawling along. Their first reaction is often one of: "there must be something wrong as the tape is moving sooo slooowly." Nope, just amazing technology. The SP speed of a VHS VCR corresponds to a linear tape speed of only 1-5/16 ips - slower than for an audio cassette deck (1-7/8" ips). EP speed is 1/3 of this - 7/16 ips. However, the effective tape speed as seen by the video heads is over 15 feet per second due to the spinning video head drum. The luminance (Y) and color (C) components of the composite video signal are recorded differently. Luminance, which is in effect the black and white picture with all the high resolution components but no color, is frequency modulated on a carrier at around 3.4 Mhz. The deviation is about 1 Mhz and the maximum frequency recorded on a VHS tape is a little over 5 Mhz (BETA is slightly different and S versions of BETA and VHS extend some of these to achieve higher bandwidths. The color signal is separated from the composite video and is amplitude modulated on a 629 KHz carrier. This is called the color under' system. The 'U' in U-Matic, a very popular industrial VCR 3/4" format (which predates Beta and VHS and is still in use) stands for this. ----------------------------------------------------------------------------- @endnode @node 3.3 "VHS audio" Sound for the VHS format is not merged into the video signal on the tape. For non-HiFi VHS VCRs, a separate stationary tape head is responsible for the audio signal. Due to the very slow tape speed, audio quality is not even comparable to a cheap audio cassette player even at the SP speed. VHS HiFi overcomes this by FM recording of the audio signal deep in the tape (recorded by a separate set of HiFi heads just before the video information), actually buried under the video information. Since the head-tape speed for the VHS audio track is the same high rate as for the video track and exceeds that of a typical audio cassette deck by a factor of more than 100, VHS HiFi audio reproduction - frequency response, signal to noise ratio, and dynamic range - is excellent and approaches that of a CD. In fact, using a T120 video cassette in EP (SLP, 6 hour) mode simply to record stereo music (with the video ignored or blanked) is extremely cost effective. What other media/technology will store a 6 hour concert with nearly perfect reproduction for under $2? (Note: if you do this, some VCRs will require some kind of video input to maintain stable tape speed. You can just ignore the video portion on audio playback.) There are two disadvantages to VHS HiFi, however: (1) there may be some degradation of video quality due to unavoidable interactions with the buried audio, and (2) it is not possible to rerecord (dub) only the audio without disturbing the video. ----------------------------------------------------------------------------- @endnode @node 3.4 "VCR servo systems" Linear tape motion and head drum rotation must be precisely synchronized during record, play, and special effects play modes. The general functioning is similar for all but the source of the basic reference signal differs for play and record. Some of the specific relationships may differ depending on the specific VCR design. Record: reference signal is vertical sync pulse from video input: o Head drum rotation is phase locked to vertical sync pulse so that appropriate head (of the A-B pair) is in contact with the tape during the appropriate video field. o The speed of the capstan which moves the tape through the transport is also locked to the vertical sync pulses so that the selected linear tape speed (SP, LP, EP) is maintained. o Control pulses (30 Hz for US NTSC) are recorded along the top edge of the tape by a stationary control head. Play: reference signal is timing pulse derived from quartz oscillator: o Capstan rotation speed is locked to a 30 Hz pulse derived from a precise quartz crystal oscillator. Head drum rotation is phase locked to the control pulses now being read off of the tape by the Control head. o The tracking control is used to adjust the relative phase of the head drum with respect to the control pulses. This permits the head path across the tape to be aligned with the actual recorded tracks. ----------------------------------------------------------------------------- @endnode @node 3.5 "Video Special effects" For CUE (fast play forward) and REV (fast play reverse), the capstan speed is phase locked to a multiple of the control track. Since the video heads are crossing multiple tracks during these modes, some noise bars are unavoidable. At SP speed, special wide or dual azimith heads are required to minimize this degradation. Thus, only 4 head VCRs can play SP tapes at fast speeds with minimal noise. With EP speed, the tracks actually overlap and a normal video head is wide enough to pick up enough signal from adjacent tracks to produce a mostly noise free picture. Due to the way adjacent tracks line up with LP speed, most of these special effects cannot be used due to serious tearing of the picture. The sophisticated processing needed for proper support at LP speed is generally not included in modern VCRs due to the apparent lack of interest in the LP speed (recording support at LP speed seems to be absent in more and more newer VCRs though they will all play back LP tapes at normal playback speed). Really slow speed is usually implemented as a variable frame advance with the tape fully stopping between frames. Special sets of video heads provide the best quality. Freeze frame (PAUSE) uses the same set of heads. As with CUE and REV, acceptable picture quality is provided even with a 2-head VCR for EP speed recorded tapes. In all cases, picture quality can be further improved through the use of a digital frame store. Note that the servo systems in consumer VCRs are rarely precise enough to implement the kind of instantaneous forward or reverse frame advance that is present in high performance (and high cost) editing decks having jog shuttle knobs with instantaneous and precise response. ----------------------------------------------------------------------------- @endnode @node 3.6 "For more information on VCR technology" The books listed in the section: @{"Suggested references" link "23.1"} include additional information on the theory and implementation of the technology of video recording and VCRs. For an on line introduction to video recording technology, point your web browser to the Magnavox reference page at the following URL: http://www.magnavox.com/electreference/electreference.html There you will find links to a number of articles on the basic principles of operation of CD players, laserdisc and optical drives, TVs, VCRs, cassette decks, loudspeakers, amplifiers, satellite receivers, and other consumer A/V equipment. ----------------------------------------------------------------------------- @endnode @node 4.1 "General VCR placement considerations" Proper care of a VCR does not require much. Following the recommendations below will assure long life and minimize repairs. o Allow adequate ventilation - VCRs are not huge users of power but there is some heat buildup nonetheless. Leave at least 1-1.5 inches around all sides and top for air circulation. Try not to place the VCR near heat producing equipment. o Do not put anything on top of the VCR that might block the ventilation grill. To be safe, don't put anything on top - period. Tapes are especially bad - for the tapes - as the heat and possible magnetic fields in the vicinity will tend to age them prematurely. o If possible, locate the VCR away from the TV. Some VCRs are particularly sensitive to interference from the TV's circuitry and while this won't usually damage anything, it may make for less than optimal performance. o Don't locate VCRs in dusty areas if possible. Consider the use of a dust cover when not actually being used if you have no choice of location. o Don't locate VCRs in areas of high (tobacco) smoke or cooking grease vapors. I cannot force you to quit smoking, but it is amazing how much disgusting difficult to remove brown grime is deposited on sensitive electronic equipment in short order from this habit. o Make sure all input-output video and audio connections are tight and secure to minimize intermittent or noisy pictures and sound. o Finally, store video cassettes well away from all electronic equipment including and ESPECIALLY loudspeakers. Heat and magnetic fields will rapidly turn your priceless video collection into so much trash. It is also recommended that you store the cassettes on edge so that the tape edges are not subject to pressing against the case and that you run them through a VCR or winder/rewinder from start to end and back on FF/REW at least once a year (another pair of recommendations that are rarely followed). ----------------------------------------------------------------------------- @endnode @node 4.2 "Preventive maintenance (PM)" You no doubt have heard that a VCR should be cleaned and checked periodically. This is basically good advice but few people actually do follow it. I cannot give a specific schedule to follow as many factors influence the amount of wear and tear on your VCR: o If you mostly use new brand-name tapes to make your own recordings, rarely play rental tapes, and have the VCR located in a clean cool relatively dust free and smoke free location, you may be able to go 5 years with no problems. However, a more prudent interval would be 1-2 years between preventive maintenance and rubber replacement after 4-5 years. Obviously, if you time shift every evening or have frequent marathon viewing parties you should probably reduce the PM interval. o If you play rental movies every weekend or older tapes and have chain smokers in the house, every 3 months may not be frequent enough. I would suggest 6 months to 1 year between preventive maintenance and rubber replacement after 3-4 years. Realistically, you are not going to do any PM anyway. So, just be aware of the types of symptoms that would be indications of the need for cleaning or other preventive or corrective maintenance - erratic loading, need to convince the VCR to perform certain operations, whirring motors without completing cycle, VCR taking longer to go into or out of a particular mode than you recall, jittery or noisy picture, or wavering or muddy sound. If your inspection reveals deteriorated rubber parts, obviously these should be replaced regardless of their age. Of course, acute symptoms like a tape jam or tape munching episode is a sign of the need for emergency treatment. This still may mean that a thorough cleaning is all that is needed. I generally don't consider cleaning tapes to be of much value for preventive maintenance since they do not run long enough or with enough force to clean the rollers, stationary heads, and guide posts. Also, the dry type, in particular, are abrasive and frequent use may cause premature wear to the expensive video heads. The following are some reasons to inspect and clean a VCR periodically: o This will maintain performance at factory new levels. Dirt, dust, and shed tape oxide all contribute to a reduction in stable tape movement and possible problems with noisy or jumping pictures and muddy or wavering sound. o Dirt, dust, and other crud can be deposited on the tapes you run through the VCR contaminating them and passing problems on to this or other VCRs in the future. o Your inspection will reveal if service parts like belts, tires, the pinch roller, etc. are in good conditions so that future surprises will be minimized. If you follow the instructions in the section: @{"General guide to VCR cleaning and rubber replacement" link "6.3"}, there is minimal risk to the VCR. However, don't go overboard. If the belts are in good condition (by appearance and stretch test), just clean them or leave them alone. This is especially true in the (generally infrequent) designs of some models of VCR tape transports where significant disassembly is required to replace a belt. In this situation, you risk not being able to put everything back the way it was. Most belts can be replaced with little or no disassembly beyond removing the top and bottom covers and possibly any circuit boards that may be in the way, Sometimes one or two additional screws will need to be loosened or removed to move a bracket or shield. ----------------------------------------------------------------------------- @endnode @node 4.3 "Rental tape considerations" It would be nice for your VCR if rental movies had never been invented. You have no idea of the history of any tape you bring home. The following may also apply to tapes in your video library or tapes given to you by friends or relatives: o The tape may be old and old tapes shed a lot more oxide and crud than newer tapes. A single playing may clog your video heads. o The tape may have been damaged by a prior viewing and one pass through may ruin your expensive video heads. A tape that has been seriously crinkled due to a VCR tape eating incident and then wound back into the cassette may be a ticking time bomb for your VCR. A tape with a partial break or one that has been improperly spliced is even more likely to cause serious damage. Do not splice tapes - see the section on @{"Recovering damaged or broken tapes" link "16.5"} o The cassette mechanism itself may have been damaged (from being dropped or stored in a hot automobile) with unknown consequences for your VCR. Note: if you should ever damage a rental tape as a result of a cranky VCR or for any other reason, don't just give it back to the video store. Please let them know. Also, if your VCR should jam with a tape inside, do not forcibly extract it - read the appropriate sections later in this document. If in doubt, let the video store know what happened and follow their recommendations. While I cannot control your viewing habits, playing a lot of old, dirty, deteriorated tapes (rental or from your own tape library) will eventually take a toll on your VCR. At the very least, you should perform a general cleaning and inspection at more frequent intervals. ----------------------------------------------------------------------------- @endnode @node 5.1 "Safety" Once you remove the cover(s) of a VCR (ignoring the warnings about no user serviceable parts, etc.), there are some risks to you and your VCR. You also, of course, void the warranty (at least in principle). Therefore, if the unit is still under warranty, having it serviced professionally may be your wisest option. Stay away from the line side of the power supply - put electrical tape over the exposed connections. To be doubly sure, tape a piece of cardboard or thick plastic over the power supply section. Other than that, there is more danger of damaging the VCR by accidentally shorting something out or breaking a little plastic doodad than of you getting hurt. o Don't wear any jewelry or other articles that could accidentally contact circuitry and conduct current, or get caught in moving parts (protect long hair as well). o If circuit boards need to be removed from their mountings, put insulating material between the boards and anything they may short to. Hold them in place with string or electrical tape. Prop them up with insulation sticks - plastic or wood. o Connect/disconnect any test leads with the equipment unpowered and unplugged. Use clip leads or solder temporary wires to reach cramped locations or difficult to access locations. o If you must probe live, put electrical tape over all but the last 1/16" of the test probes to avoid the possibility of an accidental short which could cause damage to various components. Clip the reference end of the meter or scope to the appropriate ground return. o Perform as many tests as possible with power off and the equipment unplugged. For example, the semiconductors in the switching power supply of a VCR can be tested for shorts and the fusable resistors can be tested for opens. o If you need to probe, solder, or otherwise touch circuits in a switching power supply with the power off, discharge (across) large power supply filter capacitors with a 2 W or greater 20-100K resistor and then verify with your voltmeter. o The use of GFCI (Ground Fault Circuit Interrupter) protected outlet is a good idea but will not protect you from shock from many points in a line connected power supply. A circuit breaker is too slow and insensitive to provide any protection for you or in many cases, your equipment. A GFCI may prevent your scope probe ground from melting should you accidentally connect it to a live circuit, however. o Don't attempt repair work when you are tired. Not only will you be more careless, but your primary diagnostic tool - deductive reasoning - will not be operating at full capacity. o Finally, never assume anything without checking it out for yourself! Don't take shortcuts! ----------------------------------------------------------------------------- @endnode @node 5.2 "Troubleshooting tips" Many problems have simple solutions. Don't immediately assume that your problem is some combination of esoteric complex convoluted failures. For a VCR, it may just be a bad belt or an experiment in rock placement by your 3-year old. Try to remember that the problems with the most catastrophic impact on operation (a VCR that eats tapes) usually have the simplest solutions (replace the idler tire). The kind of problems we would like to avoid at all costs are the ones that are intermittent or difficult to reproduce: the occasional interference or a VCR that sometimes will not record your favorite soaps on alternate Thursdays before a full moon. If you get stuck, sleep on it. Sometimes, just letting the problem bounce around in your head will lead to a different more successful approach or solution. Don't work when you are really tired - it is both dangerous and mostly non-productive (or possibly destructive). Whenever working on precision equipment, make copious notes and diagrams. You will be eternally grateful when the time comes to reassemble the unit. Most connectors are keyed against incorrect insertion or interchange of cables, but not always. Apparently identical screws may be of differing lengths or have slightly different thread types. Little parts may fit in more than one place or orientation. Etc. Etc. Pill bottles, film canisters, and plastic ice cube trays come in handy for sorting and storing screws and other small parts after disassembly. Select a work area which is well lighted and where dropped parts can be located - not on a deep pile shag rug. Something like a large plastic tray with a slight lip may come in handy as it prevents small parts from rolling off of the work table. The best location will also be relatively dust free and allow you to suspend your troubleshooting to eat or sleep or think without having to pile everything into a cardboard box for storage. Another consideration is ESD - Electro-Static Discharge. The electronic components in a VCR are vulnerable to ESD. There is no need to go overboard but taking reasonable precautions such as getting into the habit of touching the chassis first before any of the electronic components is a good practice. The use of an antistatic wrist strap would be further insurance. A basic set of precision hand tools will be all you need to disassemble a VCR and perform most adjustments. These do not need to be really expensive but poor quality tools are worse than useless and can cause damage. Needed tools include a selection of Philips and straight blade screwdrivers, needlenose pliers, wire cutters, tweezers, and dental picks. A jeweler's screwdriver set is a must particularly if you are working on a portable VCR or camcorder. For adjustments, a miniature (1/16" blade) screwdriver with a non-metallic tip is desirable both to prevent the presence of metal from altering the electrical properties of the circuit and to minimize the possibility of shorting something from accidental contact with the circuitry. You should not need any VCR specific tools with the possible exception of a miniature metric hex key wrench set for loosening the set screws on the roller guides should you need to perform a tape path alignment. I have never needed a VCR head puller. You can make a tool for the special nut found on many A/C head assemblies for tracking adjustment by filing a slot in the blade of a straight blade screwdriver. A low power fine tip soldering iron and fine rosin core solder will be needed if you should need to disconnect any soldered wires (on purpose or by accident) or replace soldered components. For thermal or warmup problems, a can of 'cold spray' or 'circuit chiller' (they are the same) and a heat gun or blow dryer come in handy to identify components whose characteristics may be drifting with temperature. Using the extension tube of the spray can or making a cardboard nozzle for the heat gun can provide very precise control of which components you are affecting. For info on useful chemicals, adhesives, and lubricants, see "Repair Briefs, an Introduction" as well as other documents available at this site. If you have several VCRs or do repairs for friends (former friends?), there are inexpensive kits of VCR mechanical parts like washers and springs that come in handy. General belt or similar kits are not worthwhile unless you are in the service business - there is too mach variety in the sizes and other characteristics of these types of parts to make an assortment a good investment. Note: while working with the top off, you may need to put pieces of strategically located cardboard over the area of the cassette to block extraneous light from causing erratic behavior (modes aborting, not starting at all, etc.) with the start/end-of-tape sensors. Not all VCRs are sensitive to extraneous illumination but I have been bitten more than once by not doing this. Using overhead instead of direct illumination will probably help as well. In extreme cases, placing electrical tape over the end sensors may be needed but this will likely confuse the microcontroller under certain conditions into thinking that a non- existent tape is present - or if your troubleshouting will permit, leave a cassette in the transport. (I have heard of at least one case where this was a problem even for normal operation - apparently, light was falling on the VCR in just the wrong way where it happened to be located. The VCR would enter rewind mode regardless of what the helpless human wanted unless tipped on end!) ----------------------------------------------------------------------------- @endnode @node 5.3 "Test equipment" Don't start with the electronic test equipment, start with some analytical thinking. Many problems associated with consumer electronic equipment do not require a schematic (though one may be useful). The majority of problems with VCRs are mechanical and can be dealt with using nothing more than a good set of precision hand tools; some alcohol, degreaser, contact cleaner, light oil and grease; and your powers of observation (and a little experience). Your built in senses and that stuff between your ears represents the most important test equipment you have. A DMM or VOM is necessary for checking of power supply voltages and testing of sensors, LEDs, switches, and other small components. Unless you get deep into the electronic repair of VCRs, an oscilloscope is not required. There are two items of important test equipment that you probably already have: o A video signal source - both RF and baseband (RCA jacks). Unless you are troubleshooting tuner or video/audio input problems, either one will suffice. RF sources include a pair of rabbit ears or an outdoor antenna, a cable connection, or a VCR with a working RF modulator. Similarly, a working VCR makes a handy baseband or RF signal source. o A display device. A video monitor or TV makes an excellent video signal display. Many video problems can be diagnosed by just examining the picture. If you have an old TV with a vertical hold control, this is useful when adjusting backtension, should the need arise. A B/W TV is adequate for many of the tests you will be performing. ----------------------------------------------------------------------------- @endnode @node 5.4 "Cassette cheaters" When troubleshooting mechanical problems in a VCR, one of the handiest accessories is a cassette cheater - a frame to fool the VCR into thinking there is a cassette in place so that you have access to the reel spindles and idler. You can buy these for $6-12 but you can make one that is almost as nice. Take a discarded cassette, open it up and throw away everything but the top and bottom halves and the screws. Punch out the plastic windows (and somewhat more of the top and bottom if you are so inclined). Reassemble the two halves of the cassette. Put a bit of electrical tape over the sensor holes on the sides. This will load and 'play' just fine except that some machines actually sense that the supply reel is being turned by the tape movement during loading or always and will shut down if it isn't (among other peculiarities) so you may have to do this by hand. There are several benefits to using one of these, one of which is that there is no chance of ruining a prized tape due to a hungry VCR. You will also be able to feel the spindles to get an idea whether they are turning properly and with enough torque in all modes. If you break out enough of the top and bottom, you will have access to the idler and other under-cassette parts at the same time. If you examine one of the commercial cassette cheaters, you will see that very little is needed beyond the outer frame as long as it sits properly on the indexing posts. ----------------------------------------------------------------------------- @endnode @node 5.5 "Test tapes" When aligning the tape path, a test tape will be needed as a reference. Actually, you want two - one recorded at the SP (2 hour) speed and another recorded at the EP (6 hour) speed. These do not need to be exorbitantly priced professional alignment tapes. A couple of recordings made on a known working VCR will get you close enough for most purposes. Do not use these same tapes for diagnosing or testing of mechanical problems, your VCR may be hungry and they may get eaten. For general video diagnosis including mechanical and tape eating problems, a bunch of sacrificial tapes is handy - advertizing, promos, feature shorts - anything you do not care about but have been recorded on working VCRs. Very often they get mangled and you do not want to continue to use mangled tapes which may damage the VCR - in particular the video heads. However, once you have the VCR basically working, you will want to test it start to finish on a T120 cassette. This is because the reel hub size on those short video cassettes is not the same as a standard (most commonly used) T120 cassette and may mask problems if the VCR is mechanically marginal in some respects. ----------------------------------------------------------------------------- @endnode @node 5.6 "Getting inside a VCR" You will void the warranty - at least in principle. There are usually no warranty seals on a VCR so unless you cause visible damage or mangle the screws, it is unlikely that this would be detected. You need to decide. A VCR still under warranty should probably be returned for warranty service for any covered problems except those with the most obvious and easy solutions. It is usually very easy to remove the top and bottom covers on VCRs. For the top cover, there are usually some very obvious screws on the back or sides, and in rare cases on the top. There may be a couple of screws on the bottom as well that secure the top cover. For top loaders, you will probably need to remove the cassette holder lid - there will be two screws, perhaps hidden by rubber plugs. Once all the screws are out, the top cover will lift up or slide back and then come off easily. If it still does not want to budge, recheck for screws you may have missed. For the bottom cover, there are usually a half dozen or so screws around its perimeter and sometimes in the middle as well. There may be one or two grounding screws as well which are of different length and threads - these should go back in the same location from where they came. Bottom covers are usually simple sheet metal. In rare cases, you will need to remove the front panel to free the bottom cover (or vice-versa). Circuit boards may prevent access to the top or bottom of the tape transport. Usually, removal of a few screws (often marked with red paint or arrows on the circuit board) and perhaps pressing of a couple of snaps will permit the board to be swung up on a hinge out of the way. Front panels usually snap off, possibly requiring the removal of a few screws on top or bottom. Make notes of screw location and type and store the screws away in a pill bottle, film canester, or ice cube tray. When reassembling the equipment make sure to route cables and other wiring such that they will not get pinched or snagged and possibly broken or have their insulation nicked or pierced abd that they will not get caught in moving parts. Replace any cable ties that were cut or removed during disassembly and add additional ones of your own if needed. Some electrical tape may sometimes come in handy to provide insulation insurance as well. ----------------------------------------------------------------------------- @endnode @node 5.7 "Why does my VCR shut down or behave strangely when I remove the cover?" There are various sensors in a VCR that are light sensitive - it is not a safety interlock (though it acts this way in some VCRs) but a result of the way the tape start and end sensors operate. VHS tapes have a clear leader and trailer. An LED or light bulb poking up near the center of the cassette shine towards sensors at either side of the cassette. When light is detected the VCR assumes that it is at the appropriate end of the tape and shuts off (or rewinds if in PLAY mode when it senses the end depending on model). During servicing, a piece of opaque cardboard or other insulating material should be placed above the cassette basket if any strange behavior is detected that was not present with the cover in place. Not all VCRs are particularly sensitive external illumination. ----------------------------------------------------------------------------- @endnode @node 5.8 "Getting built up dust and dirt out of a VCR" This should be the first step in any inspection and cleaning procedure. Do not be tempted to use compressed air! I would quicker use a soft brush to carefully dust off the circuit boards and power supply. Work in such a way that the resulting dust does not fall on the mechanical parts. For the deck itself, using compressed air could dislodge dirt and dust which may then settle on lubricated parts contaminating them. High pressure air could move oil or grease from where it is to where it should not be. If you are talking about a shop air line, the pressure may be much much too high and there may be contaminants as well. A Q-tip (cotton swab) moistened with politically correct alcohol can be used to remove dust and dirt from various surfaces of the deck (in addition to the normal proper cleaning procedures for the guides, rollers, heads, wheels, belts, etc.) ----------------------------------------------------------------------------- @endnode @node 5.9 "What to do if a tiny tiny part falls into the VCR" We have all done this: a tiny washer or spring pops off and disappears from sight inside the guts of the unit. Don't panic. First - unplug the VCR if it is plugged into the AC. Remove the battery pack from a camcorder. Try to locate the part with a bright light without moving the VCR. You may have gotten lucky (yeh, right). Next, over an area where a dropped part will be visible (not a shag carpet!), try any reasonable means to shake it loose - upside down, a little gently tapping and shaking, etc. A hard surface is better in some ways as you might hear the part drop. On the other hand it may bounce into the great beyond. If this does not work, you have two options: 1. Assume that the part has landed in a place that will not cause future problems. There could be electrical problems if it is metallic and shorts out some circuitry or there could be mechanical problems if it jams some part of the mechanism. There is an excellent chance that the part will never cause any harm. What chance? I don't know, maybe 99%. It is not worth taking the unit to pieces to locate the part. You are more likely to damage something else in the process. Obtain a replacement and get on with your life. The exception is, of course, if you now begin experiencing problems you **know** were not there before. 2. Take the unit to pieces in an attempt to locate the part. For all you know, it may be clear across the room and you will never find it inside. If all the gymnastics have not knocked it loose, then it may be really wedged somewhere and will stay there - forever. If the VCR behaves normally, then in all likelihood it will continue to do so. To prevent this sort of thing from happening in the future you will no doubt be much more careful. In addition, consider constructing a paper dam around the area when you are attempting to remove a reluctant E-clip or spring. Keeping one finger on the part as it is removed will tend to prevent uncontrolled ejection as well. ----------------------------------------------------------------------------- @endnode @node 6.1 "Parts of the tape transport in a VCR" The following description applies to 99.9% of the VCRs in existence today. I have seen one that had a sideways loading mechanism - very weird. Looking at the unit from above with the front toward you: o Supply reel - left hand side platform on which the supply tape spool sits. Edge which contacts idler tire should be cleaned. o Takeup reel - right hand side platform on which the takeup tape spool sits. Edge which contacts idler tire should be cleaned. o Idler - assembly which swings between supply and takeup reels and transfers power to the appropriate reel to wind the tape up during play and record and often to drive FF and REW. o Idler tire - the black rubber ring on the outside of one part of the idler which actually contacts the reel edges. This is single most likely part to need replacement after a few years of use. Some VCRs use a gear instead of a tire, but the tire is most common, especially in older units. Clean and inspect - replace if in doubt. Some VCRs use gears in place of rubber. Teeth can break off but these are generally quite reliable. Some high-end decks may have separate motors for reel rotation. o Roller guides - there are two, one on each side. These assemblies move from their retracted position toward front of machine to their loaded position for play and record. The white rollers should spin freely and be clean. When retracted, the roller guide assemblies will be slightly loose. However, when the tape is wound around the video head drum, they must be snug against the V-stoppers - the brackets at the end of the tracks. Also on the same assembly are tilted metal guide posts - again one for each side. These sometimes fall out with obvious consequences. Proper functioning and adjustment of the roller guides is the most critical requirement for proper tracking. (However, do not touch their settings without being really sure that they are at fault and not until you have read the sections relating to @{"tape path alignment" link "19"}) Clean and inspect. o Video head drum - almost 3 inch diameter by 3/4" high contains the video heads (and HiFi audio and flying erase heads, if present). Stay away from this unit - video heads are very delicate. If you must clean it, refer to the specific instructions on cleaning video heads elsewhere in this document. Video heads do not normally require cleaning despite what the cleaning tape people will have you believe. If you are not having video noise problems, they should be left alone. o Capstan - right side after tape exits from roller guide. The capstan is a shaft about 3/16" diameter which during play and record (and search) modes control tape movement forward or reverse when the pinch roller is pressed against it. Should be cleaned to assure proper tape movement during play, record, and search modes. o Pinch Roller - black rubber roller about 1/2" diameter, 3/4" high which spins freely and is pressed against the capstan during play, record, and search modes. A hard, shiny, dried out pinch roller can lead to tape edge munching and erratic sound/speed/tracking. Clean thoroughly. Inspect for cracked or deteriorated rubber. o Audio/Control Head assembly - between right roller guide (when tape is loaded around drum) and capstan. Includes magnetic heads for non-hifi (linear) audio and synchronization control track. Should be cleaned since tracking and non-hifi audio performance is critically dependent on its performance. o Back-Tension Arm - left side just as tape exits cassette - this is coupled to a felt band and serves to maintain a constant tension on the tape during play, record, and forward search. Retracts toward cassette when tape is unloaded. Backtension is somewhat critical and may need adjustment after long use. o Various other guide posts - vertical stationary metal posts which tape contacts. Should be cleaned but rarely need adjustment. o Full erase head - left side towards rear which tape passes over just before going around roller guide, guide post, and drum. Rarely causes problems. Clean. o Impedance Roller - left side near full erase head. Freely rotating roller stabilizes tape movement. Clean. o Belts - various size black rubber bands - a typical VCR will have between 0 and 12 of these on top and bottom. Typical is 3 or 4. These will need replacement after a few years. Clean and inspect. ----------------------------------------------------------------------------- @endnode @node 6.2 "Most common problems" o VCR refuses to FF or REW and shuts off. o VCR shuts off entering PLAY or REC or at random during PLAY or REC. o VCR eats tapes. o VCR doesn't accept tapes or ejects them without cause. o Sound is wavery, fluctuating, or muddy. The cause for all of these is very often a bad idler tire or other dirty, worn, or tired rubber parts. See the section below: @{"General guide to VCR cleaning and rubber replacement" link "6.3"} A VCR that just munched down your favorite tape is very likely only in need of a little tender loving care. ----------------------------------------------------------------------------- @endnode @node 6.3 "General guide to VCR cleaning and rubber parts replacement" All the guideposts, wheels, and rubber parts of a VCR should be cleaned periodically - how often depends on usage. Of course, no one really does it unless something goes wrong. Do not attempt to clean the video heads until you follow the proper procedure given elsewhere in this document, you can break them - very expensive lesson. In most cases, they do not need attention anyhow. Q-tips and alcohol (91% medicinal is ok, pure isopropyl is better. Avoid rubbing alcohol especially if it contains any additives) can be used everywhere except the video heads. Just dry quickly to avoid leaving residue behind or damaging the rubber parts further. Cleaning may get your machine going well enough to get by until any replacement rubber parts arrive and to confirm your diagnosis. Things to clean: 1. Capstan and pinch roller. These collect a lot of crud mostly oxide which flakes off of (old rental) tapes. Use as many Q-tips (wet but not dripping with alcohol) as necessary to remove all foreign matter from the capstan (the shiny shaft that pulls the tape through the VCR for play and record). Just don't get impatient and use something sharp - the crud will come off with the Qtips and maybe some help from a fingernail. Clean the pinch roller (presses against the capstan in Play, Record, and Search mode CUE and REVIEW) and until no more black stuff comes off. Use as many Qtips as necessary until no more black gunk collects on Q-tip. If the pinch roller is still hard, shiny or cracked, it will probably need replacement. Many are available for about $6 from the sources listed at the end of this document. It is sometimes possible to put the pinch roller in an electric drill, drill press, or lathe, and carefully file off the hard shiny dried out rubber surface layer, but only use a last resort - and this fix is probably temporary at best. 2. Various guideposts including the roller guides (the white rollers on metal posts which are near the video head drum when in play or record mode). When in FF or REW, or with no tape present, these move on tracks to a position toward the front of the VCR. Note that the roller guides with the white rollers and tilted metal posts will be fairly loose when in the unloaded position (but you should not be able to lift them off the tracks). When actually playing or recording a tape, they will be snug against the stoppers at the end of the tracks. 3. Idler tire (idler swings between reels and transfers motor power to reels - clean until no more black stuff comes off. A dirty or worn idler tire is probably the single most common VCR problem. If the idler tire appears cracked, glazed, or dried out, it will need to be replaced. About $.50-$1.00. As a temporary measure, you can usually turn the tire inside-out and replace it. The protected inner (now outer) surface will grip well enough to restore functionality until a replacement tire arrives - and verify the diagnosis as to the cause of your problem. Also, the idler assembly includes a slip clutch. If this weakens, the idler may not have enough force to press on the reel table edges. If it becomes too tight, there may be audio, video, or crickled tape problems and/or excess wear of the idler tire. When in doubt, the entire idler assembly is often available as a replacement part. They can often be disassembled and adjusted if necessary. 4. Reel table edges - surface on the reel tables where the idler contacts. 5. Audio/control head (right side) and full erase head, (left side). Q-tips and alcohol are ok for these. 6. Anything else that the tape contacts on its exciting journey through your machine. 7. Rubber belts. Access to some of these will probably require the removal of the bottom cover. After noting where each belt goes, remove them individually (if possible) and clean with alcohol and Qtips or lint free cloth. Dry quickly to avoid degrading the rubber from contact with the alcohol. If a belt is trapped by some assembly and not easy to remove, use the Qtip on the belt and/or pulley in place. However, if it is stretched, flabby, or damaged, you will need to figure out how to free it. Make sure that there are no twists when a square cut belt or replacement is installed on its pulleys. On some models, you may need to unscrew circuit board(s) blocking access to either the top or bottom of the tape transport. Make notes of what went where - particularly different types of screws and routing of wires. Any belts that appear loose, flabby or do not return instantly to their relaxed size when stretched by 25% or so will need to be replaced and may be the cause of your problems. Belts cost about $.30-$2.00 and complete replacement belt kits are often available by model for $3.-$12. Meanwhile, the belts will function better once they are cleaned, maybe just enough to get by until your replacements arrive. 8. Video heads: READ CAREFULLY. Improper cleaning can ruin the expensive video heads. DO NOT attempt to clean the video heads without reading and following the procedure described in the section on @{"video head cleaning" link "18.4"} While VCRs should be cleaned periodically, the video heads themselves usually do not need cleaning unless you have been playing old or defective rental tapes which may leave oxide deposits on the tips of the delicate ferrite head chips. Unless you are experiencing video snow, intermittent color, or loss of or intermittent HiFi sound (HiFi VCRs only, the HiFi heads are located on the video head drum and for the purposes of cleaning, treated the same way) leave the video heads alone. If you really feel that video head cleaning is needed, refer to the sections on @{"video head problem diagnosis and cleaning" link "18"} elsewhere in this document. ----------------------------------------------------------------------------- @endnode @node 6.4 "Lubrication of a VCR" The short recommendation is: Don't add any oil or grease unless you are positively sure it is needed. Most parts in a VCR are lubricated at the factory and do not need any further lubrication over their lifetime. Too much lubrication is worse then too little. It is easy to add a drop of oil but difficult and time consuming to restore a VCR that has taken a swim. NEVER, ever, use WD40 in a VCR! WD40 is not a good lubricant despite the claims on the label. Legend has it that the WD stands for Water Displacer - which is one of the functions of WD40 when used to coat tools. WD40 is much too thin to do any good as a general lubricant and will quickly collect dirt and dry up. A light machine oil like electric motor or sewing machine oil should be used for gear or wheel shafts. A plastic safe grease like silicone grease or Molylube is suitable for gear teeth, cams, and the roller guide tracks. Unless the VCR was not properly lubricated at the factory (which is quite possible), the only likely areas needing lubrication are the roller guide tracks - clean and grease. Sometimes you will find a dry capstan, motor, lever, or gear shaft but this is less likely. In general, do not lubricate anything unless you know there is a need. Never 'shotgun' a problem by lubricating everything in sight! You might as well literally use a shotgun on the VCR! ----------------------------------------------------------------------------- @endnode @node 6.5 "Head demagnetizing" With audio tape decks, demagnetizing is often recommended to improve sound quality and frequency response. There is some debate as to how much benefit there is to this practice but if done properly, there is little risk. Demagnetizing removes the residual magnetic fields that can build up on ferrous parts of the tape heads and various guideposts and other parts in the tape path which may affect frequency response. For the following, do not go near the video head drum, only perform demagnetization of the stationary A/C head, erase head, and guide posts and rollers. In my opinion, the video heads should almost never need to be demagnetized. The ferrite material from which they are constructed is not prone to easily being magnetized like steel. Use a small demagnetizer designed for a tape deck or cassette deck. Do not use anything homemade that might be too powerful or a bulk tape eraser which would certainly be too powerful. Make sure the tip is covered with a soft material to prevent damage to the finely polished surfaces in your VCR. Turn power on to the demagnetizer when a couple of feet away from the VCR. Then, slowly bring it in close and slowly go over all surfaces of anything that the tape contacts or comes close to in the tape transport. The key word here is SLOWLY. Move fast, and you will make the magnetic fields stronger. When finished, slowly draw the demagnetizer away to a distance of a couple of feet before turning it off. ----------------------------------------------------------------------------- @endnode @node 7.1 "Cassette loading and eject problems" Cassette loading places the cassette into proper position on the tape transport. In a front loader, pushing the cassette gently into the slot should cause a motor to take over and suck it in and down to rest on indexing pins. The mechanism that actually holds the cassette is called the cassette basket. Several types of problems are possible: the VCR may ignore you when you push the cassette in or press EJECT, or it may spit it out immediately or cycle back and forth. On a top loader, you do most of the cassette loading manually, so the only likely problem will be if EJECT does not work. If attempting to load a cassette produces no response (though the VCR has power), then there could be a problem with the microswitch that senses the presence of a cassette, the cassette loading motor (if separate from the main motor), a slipping or broken belt, or a faulty driver or other electronic problem. Sometimes this could mean that the microcontroller is confused due to a faulty mode switch or because the mechanism somehow got into a peculiar state. Manual cycling of the cassette loading mechanism might reset it. Gently push a cassette in and turn the appropriate shaft or pulley by hand. First, try this with the VCR unplugged. If nothing happens or you feel resistance, try the other direction. Assuming you find no problems - there is no significant resistance to your turning and the cassette basket cycles from fully ejected to fully seated on the transport baseplate, leave the cassette basket in a partially loaded position and plug the VCR into the AC power and turn it on (this may not be necessary depending on the design of your VCR). It should now reset itself and either load or eject the cassette. If there are still no signs of a response, a power supply, motor, or electronic problem is likely. If you hear a motor whirring but nothing happens, this is almost certainly a slipping or broken belt. If pushing a cassette into the VCR results in it being ejected as though it tasted really bad (there may or may not be hesitation), or if the cassette cycles back and forth without stopping, there could be several possible causes. If it stops part way during loading, does it pause as though the motor is straining or just abort with no warning? If the former, then check carefully for foreign objects, or lack of lubrication. A typical cause is a belt slipping, usually not the idler in this case. Help it out gently and see if that will complete the cycle. Sometimes it is helpful to cycle the mechanism by hand - turning the appropriate shaft or pulley and feeling and watching for any place where it binds. If the basket moves in the wrong way or you feel any significant resistance, try the other direction. Sometimes, the sticky cassette labels partially or totally peal off and clog the works. You may find a toy or rock inside carefully inserted by your 3 year-old! If the microcontroller were detecting an abnormality, then it would abort instantly but would most likely try to unload the tape before giving up. It is possible that if the expected behavior is not produced by the end/beginning-of-tape sensors during cassette loading, an abort could be initiated. Therefore, these sensors could be suspect. In some cases, the mode switch may be dirty or faulty. A gear may have broken some teeth or slipped a couple of teeth and the timing relationships may be incorrect. There may be a microswitch that is controlled by the cassette basket position and this may be defective or dirty. Similarly, if the cassette seems to be cycling in and out in an apparently infinite loop, there may be an obstruction or the microcontroller is confused by a bad sensor or the basket is out of synchronization with the rest of the mechanism. A squirt of contact cleaner into the microswitch sensor and/or reflowing its bad solder connections may solve this type of problem. Similar comments apply to cases where pressing the EJECT button produces no response. In particular, if the cassette was loaded successfully and you just finished a thoroughly enjoyable movie, the microcontroller may think the mechanism is not safe and is not ejecting to protect your valuable tape from possible damage should it not be fully retracted into the cassette. ----------------------------------------------------------------------------- @endnode @node 7.2 "Ejecting a cassette from an uncooperative VCR" It is a common experience - the rental movie is due back at the video store NOW but no matter how you press the EJECT button, yell, scream, hold your breath, or jump up and down, the cassette refuses to be appear. To remedy the underlying problem, see the sections on: @{"Cassette loading and eject problems" link "7.1"} and other for appropriate information. This section only deals with getting the cassette out without damaging either your valuable recording or VCR. Under no circumstances should you force anything - both your tape and your VCR will be history. First, see if the VCR just got into a confused state - pull the plug and patiently wait a minute or two. This may reset the microcontroller and all will be well. These things happen. If this is not successful, you will need to open up the VCR (unplug it first!) and attempt to cycle the mechanisms by hand. Probably both top and bottom covers will need to be removed. The following procedures assume that there are no broken parts, foreign objects, or other damage which might prevent manual cycling of the tape loading and cassette loading mechanism. (Inspect for toys and rocks.) Also note that some VCR designs use solenoids to engage various operations. This will complicate your task (to put it mildly) as locating and activating the proper ones at the appropriate time is, well, a treat. 1. Tape unloading: The first step is to determine if the tape has been unloaded from the video head drum back into the cassette. If the tape is fully retracted into the cassette - there is no tape showing, then go on to step (2). If not, you will need to figure out which shaft or pulley to turn to unload the tape. Trace the linkage or gears that move the roller guides back to their motor - it may be the main capstan motor or a separate small motor used only for this purpose. Rotate this in the direction which moves the roller guides back towards the cassette. It will take many revolutions - be persistent. If you feel any significant resistance or the roller guides move out toward the drum, turn the other way. The tape is fully unloaded when the roller guides are all the way into the cassette and the tape is straight across the cassette's stationary guideposts. If a single motor performs both the tape loading and cassette loading functions, stop turning as soon as you see the cassette start to rise and read the @{"next section" link "7.3"} before proceeding. If you are not fully successful or if there is still a tape loop outside the cassette even once you have been turning for what seems to be an eternity, you can still try to eject the cassette but will need to be extra careful not to crinkle the tape as the cassette door closes with the tape sticking out. Before proceeding on in this case, try to find a way to turn one of the reels to pull that tape back in as this will make your task a lot easier. 2. Cassette unloading. Once the tape is fully retracted into the cassette, the cassette can be ejected safely. If a tape loop is still sticking out of the cassette - and you care about the recording - you will need to be especially careful not to crinkle the tape as the cassette door closes. It is usually not possible to get the cassette fully out without its door closing, so the best you can do is to make sure when this happens, the tape is flat across the gap. With care, it should survive. On a top loader, there is usually a solenoid specifically for EJECT or a simple mechanical pushbutton. Once the appropriate lever is pressed, the cassette should pop up - hold the basket with one hand as you do this to prevent any exposed tape loop from being crinkled. On a front loader, locate the cassette loading motor and begin turning it in the appropriate direction - this will be fairly obvious assuming there are no broken gear teeth or other broken parts and that something isn't totally jammed. If this is the main capstan motor, then just continue turning as in (1). Eventually the cassette should raise up and out. If you have a tape loop, be extra careful not to catch it on any guideposts or obstructions as you remove the cassette. Then, wind it back into the cassette by turning one of the reels (you may have to depress the release button on the bottom of the cassette with a pencil - this is the small hole in the center near the label side.) ----------------------------------------------------------------------------- @endnode @node 7.3 "VCR is confused - will not eject non-existent tape" If for some reason, the microcontroller gets confused and refuses to raise the basket and there is no tape in the VCR, first, try pulling the plug for a minute or two. This may reset the error condition. However, since the mechanism is in an illegal state, the microcontroller may refuse to do anything for fear of making things worse. Assuming that the problem is still present, here are two suggestions: o Manually turn the appropriate motor shaft with power off to put the mechanism through the eject cycle. In many VCRs, this is as simple as turning the EJECT motor or possibly the main motor. Be patient and gentle - it will take a while. If there is some underlying problem which caused the basket to be lowered without a cassette in place, than the VCR may return to the illegal state, do nothing, or do something else that is peculiar once power is restored or any button is pressed. o Convince the microcontroller that a tape really is present when there is none. You need to (1) cover the start/end sensor LED poking up in the center of the deck, (2) depress any other microswitches that sense tape present, press EJECT, and (3) possibly turn the non-driven reel by hand a bit while it is attempting to wind the tape loop back into the cassette. Three or four hands are a definite asset. Make sure you get your fingers out before they are caught! Again, an underlying problem may produce unexpected results. For additional info on initialization problems, see the section: @{"VCR is failing the power-up sequence" link "10.6"} ----------------------------------------------------------------------------- @endnode @node 8.1 "VCR will not fast forward and/or rewind" Usually, the owner will admit that the machine is pre-Jurassic and has never been cleaned or serviced. Anyway, rule out the idler tire as well as the idler clutch - if it weakens, then the idler wheel does not press against the appropriate reel with enough force to grip. Is it s top or front loader? If a top loader, you should be able to trick it into playing a nonexistent tape by covering up the end-of-tape light (the one sticking up in the middle) so that it will think there is a tape inserted. (In some models, there might also be a microswitch.) This may permit you to see what is going on. If a front loader, then it is tougher. You need a cassette cheater (see the section on @{"Cassette cheaters" link "5.4"}). Then, with the cheater in place happily fooling the VCR, feel the spindles while the machine is operating. In FF or REW, you may find that they are not being driven or or being driven very weakly. Try to determine if the idler is even being pushed into position or is hung up on something. If there is any chance that it is the idler tire, try turning it inside-out. The relatively protected inner (now outer) surface may grip well enough to confirm the diagnosis. Has it been serviced in the last 15 years? The last 100 years? ----------------------------------------------------------------------------- @endnode @node 8.2 "VCR aborts fast forward or rewind" In this case, the tape starts to move - possibly at a reasonable speed - but then may shut down - possibly erratic or tape dependent. Make sure the tape is not the problem - try another one. If it starts the operation (as evidenced by whirring sounds and the tape counter changing numbers) but at some point - perhaps near the end of the tape - aborts and shuts down, then a worn idler tire, worn or broken idler clutch, bad belt, or lubrication problem is likely. See the section: @{"VCR will not fast forward or rewind" link "8.1"} as well as @{"Lubricating a VCR" link "6.4"} With instant start transports - where the tape is maintained around the video head drum for all but the fastest rewind, there could be other control problems as well. If the tape starts fast forwarding or rewinding properly (from a visual inspection with the cover off) but the tape counter does not change value and then the unit shuts down, a reel rotation sensor problem is likely. See the section: @{"Reel rotation sensors" link "20.4"} ----------------------------------------------------------------------------- @endnode @node 8.3 "Tape rewinders" Should you buy a tape rewinder to save wear and tear on your VCR? Take it or leave it. I think they are good if your VCR is old and for whatever reason has trouble with FF or REW. However, sluggish FF or REW may be a precursor to tape eating and should be addressed to avoid an impending failure which may ruin a tape. Rubber parts deteriorate by just existing. The surface layer oxidizes and use may actually be good (don't quote me!). I would not bother with a rewinder just to prevent wear and tear on the motors or heads. In many VCRs - particularly older VCRs without real-time tape counters, the tape is totally retracted into the cassette during high speed FF or REW and does not contact the heads at all. In newer VCRs with real-time counters, the tape will contact the control head lightly but wear should not worth worrying about. Wear and tear on the motors is not a serious problem - much less than playing a tape. If the convenience of being able to rewind off-line is important to you, then there may be no harm in using one. However, some rewinders can be hard on video tapes as they usually do not sense the clear leader but stop rewinding when the tape tension increases at the end of the tape. This may eventually damage the tape and/or pull the tape from the takeup reel hub. I have heard of some actually mangling tapes. ----------------------------------------------------------------------------- @endnode @node 9.1 "VCR refuses to record" If efforts to record (directly or via the timer) are totally ignored or cause the cassette to be ejected, then the record protect tab on the cassette may be broken off or the record protect sense switch in the VCR may be dirty or defective. This switch sits just under the cassette slot (on front loaders). Locate it by referencing the tab position on the loaded cassette. It can easily be tested with an ohmmeter - if you can get to it. To confirm, short out or disconnect (which you will need to do depends on the design of your VCR) the appropriate wires (maybe there is a connector - this could have bad contacts as well) and see if the VCR is more cooperative. ----------------------------------------------------------------------------- @endnode @node 9.2 "VCR aborts play or record during startup or shortly thereafter" This is a problem with the process called 'tape loading' - pulling the tape loop out of the cassette and wrapping it around the spinning video drum, engaging the capstan and pinch roller and reel rotation. Check all the belts above and below the deck. Belts can appear to be firm but if they do not return immediately to their relaxed length when you stretch them 25%, they will need to be replaced. With the cover off, observe the behavior when you hit play. (You may need to put a piece of cardboard over the cassette to block external light from interfering with the start/end tape sensors). Assuming this is a basic VCR (no instant start features), you should see: 1. The video head drum begins to spin. 2. The roller guides move smoothly on the tracks, wind the tape around the drum, and stop snuggly pressed against the 'V-stopper' at the end of the tracks. 3. The pinch roller moves into position and presses the tape against the capstan. 4. The tape begins to move and is wound up by the takeup reel. 5. The picture and sound appear on the TV. With a 'rapid or quick start' (or it may be called something else) transport, the tape moves to a half-loaded position when the cassette is inserted. This is at an intermediate position partially pulled out of the cassette but not wrapped around the drum. On VCRs with a real-time counter and/or index search capabilities, the tape will be in contact with the control head. With an 'instant start' transport, the tape will fully load around the spinning drum when the cassette is inserted but the capstan will not engage and no tension will be applied to the tape until you press PLAY or REC. (After about 5 minutes, the drum will stop and it may unload to the half loaded or unloaded position.) Note that for VCRs with a real-time counter and/or index search capabilities, the tape must be in contact with the control head (but not the video heads) for all relevant modes. These VCRs (which include many modern units) must therefore pull the tape at least partly out of the cassette. In all cases, the completion of the sequence results in approximately the same mechanical configuration during PLAY. Several likely possibilities when it shuts down: 1. Everything occurs as above, picture and sound appear for a few seconds, but then the VCR unloads the tape, ejects the cassette, goes into REW mode, stops, or shuts off. Two common causes: The takeup reel does not turn and tape spills into the machine. This is sensed by the microcontroller which aborts record or play and attempts to save your valuable cassette. Most likely cause: old/dirty idler tire. As a test, turn the idler tire inside-out. The fresh surface will now work well enough to confirm this diagnosis and will continue working long enough for your replacement idler tire to arrive. See the section: @{"General guide to VCR cleaning and rubber parts replacement" link "6.3"} The takeup reel is turning properly but one of the reel rotation sensors or its electronics is defective. As a test, check to see if the tape counter is changing at any time during the loading and abort process. Non-real time tape counters usually get their pulses from this same sensor. (Real time counters operate off of the A/C head control pulses and therefore would not be affected by a defective reel sensor). Some older VCRs used a belt driven counter - the belt may have broken or fallen off. Most newer VCRs use an optical sensor which may simply be dirty. See the section on: @{"Reel rotation sensors" link "20.4"} 2. The roller guides are getting hung up and not fully loading the tape either as a result of an obstruction or dried up grease, or a slipping tape loading belt (often accompanied by an spine tingling squeal). Parts may have broken or fallen off of the roller guide assemblies preventing them from fully engaging the 'V-stoppers'. A similar fault may prevent the capstan from fully engaging against the tape and pinch roller. 3. The mode switch sensor is dirty or defective and confusing the poor microcomputer as to the position of the loading mechanism. In this case, the loading process may stop half way, pause, and then unload as in (1) or (2), above. Or, it may do almost anything. See the section on: @{"Erratic behavior in various modes" link "10.2"} 4. Some other condition such as the end-of-tape sensor thinking that you are at the end of the tape is aborting the tape loading process. This might be indicated by a sudden reversal and shutdown rather than a pause (usually accompanied by the sound of a motor whirring) at some point attempting to complete part of the cycle. For problems with record in particular, the record protect tab switch may be dirty or worn resulting in random aborts. 5. Electronic problems like bad grounds or other bad connections are alos possible. Since with some models, (a number of JVC manufactured VCRs, for example) ground integrity is via screws through the mainboard, should these loosen, erratic behavior may result. Tighten the screws. 6. A defective microcontroller or other logic could also be at fault but this is less likely than any of the preceding. ----------------------------------------------------------------------------- @endnode @node 9.3 "VCR aborts play or record at random times or near end of tape" In this case, the VCR starts to play or record but, say, an hour later, shuts down for no good reason - at least not as a result of a command you thought you issued. Make sure the tape is not the problem - try another one. Confirm that you are using the proper play or record modes - not OTR (One Time Record) or other timed play or record modes which will likely operate in increments of 15 minutes depending on how many times you press the button. In addition, on certain VCRs, if the program timer is enabled with a program setting that has its stop time occur while you are using the VCR - even if the record operation has been aborted by pressing the stop button - the VCR will shut down. Finally, make sure you are not using any 'insert editing' modes which require a previously laid down control track and would abort once blank tape was reached. See the section: @{"Recording stops at random times on previously used tapes" link "11.4"} Once all the obvious problems and cockpit errors have been eliminated, mechanical problem still likely even though the VCR does not abort immediately. A worn idler tire, worn or defective idler clutch, bad belt, or improperly adjusted backtension, are all possibilities. This is particularly likely if the problem is more likely to occur or only happens near the end of tapes as the required takeup reel torque is greater and any of the above mechanical problems will be exacerbated. With instant start transports - where the tape is maintained around the video head drum for all but the fastest rewind, there could be other control problems as well. If the operation starts properly (as indicated by a changing picture on the TV in play or from a visual inspection with the cover off) but the tape counter does not change value and then the unit shuts down, a reel rotation sensor problem is likely. See the section: @{"Reel rotation sensors" link "20.4"} This could still be due to problems similar to those which cause an immediate abort if some components or connections are marginal. Also see the section: @{"VCR aborts play or record during startup or shortly thereafter" link "9.2"} ----------------------------------------------------------------------------- @endnode @node 9.4 "VCR eats tapes" The most common cause of a VCR eating tapes is a dirty/worn idler tire preventing the takeup reel from turning. See section on @{"General guide to VCR cleaning and rubber parts replacement" link "6.3"} The idler tire transfers motor power to the appropriate reel hub. If dirty, worn, dried out, glazed, cracked, or otherwise deteriorated, it will slip and cause the takeup reel (in play mode) to stop turning at some point. Hopefully, the microcomputer senses this and tries to wind the tape back into the cassette. But, you guessed it, this requires the idler tire so you end up with a mess of tape inside the machine. When you go to eject, you may get the cassette with a tape loop hanging out. If you are careful, you may be able to extract the tape without crinkling it too badly but don't just pull - it will break or be hopeless damaged. You will need to remove the top cover and carefully lift the tape loop out of the machine and wind it back into the cassette. If there is any significant crinkling or a partial break in the tape, discard the cassette. If it is priceless and irreplaceable, see the section: @{"Recovering damaged or broken tapes" link "16.5"} DO NOT try to use it or just return it to the video store without informing them of what happened - it is unfair to the next renter as a badly crinkled or partially broken tape can destroy expensive video heads. ----------------------------------------------------------------------------- @endnode @node 9.5 "Tape loop hanging from cassette when ejected after play or record" (This may also apply to other modes for a VCR with a 'quick start' or 'instant start' transport.) If your VCR aborts playing unexpectedly and shuts down and then, pushing EJECT results in a tape loop hanging out of the cassette when it is removed, this is considered tape eating - refer to the section: @{"VCR eats tapes" link "9.4"} However, if all other functions work normally but ejecting results in a tape loop, this section is for you. Using a garbage cassette, try to observe exactly what is happening during EJECT. Specifically, is the operation terminating early or is there some problem with the appropriate reel not turning or not turning reliably or quickly enough? Is the tape getting hung up on the roller guides or on some other guideposts? As with tape eating, the most common cause is dirty, old, deteriorated rubber parts - particularly the idler tire - preventing the tape from being fully wound back into the cassette. Therefore, the first step is to follow the procedures in the section @{"General guide to VCR cleaning and rubber parts replacement" link "6.3"} If this only started happening after you had the VCR apart for any reason, recheck your work - you may have neglected a connector, have the mode switch slightly out of position, or have gears which are improperly timed. Many VCRs determine that the tape is completely wound back into the cassette by sensing rotation of the non-driven reel indicating that the tape is pulling on it as a result of being tight and pulled by the driven reel. If this sensor is defective, disconnected, the signal is noisy, or the associated electronics are faulty, the operation may be terminating early. As an experiment to confirm this, use a cassette cheater and while the VCR thinks it is winding the tape back into the cassette, turn the non-driven spindle by hand - this should stop the operation instantly. If it stops too quickly - before you turn the spindle, there could be a problem with this sensor. It is also possible for a failure of one of the reel brakes to allow one of the reels to continue spinning even after motor power has been shut off. Alternatively, a sticky brake band may increase the driven reel torque and fool the microcontroller into thinking that the tape slack has been taken up. If the roller guides get hung up on the tracks while being retracted, even for an instant, the tape may become tight around the roller guides, pull on the non-driven reel, and stop the operation before the tape is fully wound back into the cassette. Check for obstructions and for adequate lubrication of the roller guide tracks. If it is a late model Sony, the 'half loading arm' could need lubrication. See the section: @{"Late model Sony VCR munches tape on eject" link "17.4"} ----------------------------------------------------------------------------- @endnode @node 9.6 "Tape sticks to head drum" (From: Daniel Schoo) This seems to happen mostly on machines with a lot of play time. There is supposed to be an air film between the tape and drum to facilitate the reduction of friction. When the drum gets worn and polished the air is squeezed out and the tape sticks. Little can be done for this. You could replace the drum but this is expensive and not worth the effort for most machines. The other option is to try and rough up the drum surface by light sanding with scotchbrite. I don't need to go into detail about how difficult this is to do correctly but what the heck you don't have anything to loose. Just be careful and stay clear of the heads. BTW I have seen "cleaning" tapes that rough up the drums very well! Picture jittering vertically may be similar problem. Tape is not moving smoothly over the head drum. ----------------------------------------------------------------------------- @endnode @node 9.7 "Video head drum stops or slows during play or record" Check whether the backtension on the tape is applying so much pressure to the drum that it is slowing it down. Backtension should be just enough to keep the tape in good contact with the drum. If it is too tight, then you backtension felt may be worn or adjusted too high. There is a lever just as the tape exits the cassette - push this to the right to reduce tension. Someone may have attempted to repair a broken backtension band and reduced its length - I got a VCR for repair once where this was done. If it is not the backtension, check free rotation of the drum when it stops - I bet it turns as freely as always. Could be a part in the motor driver that is faulty and failing when hot. However, the bearing could be worn or dry which would require disassembly and lubrication or replacement of the lower cylinder (assuming this is where the drum bearings are located). ----------------------------------------------------------------------------- @endnode @node 10.1 "VCR is alive but will not do anything" Typical symptoms: front panel display is active, it may be possible to set the clock or timer and change channels, but all transport related buttons are totally inert. It is likely that the VCR refuses to accept a cassette as well. This could mean many things including motor problems as well as a general power supply or control system failure. However, here are a couple of things to try first: 1. Cycle power - unplug the VCR from the wall (don't just use its power switch) for a minute or two to see if the microcontroller simply got into a confused state. This is more common than you would think. A random power surge can do it. The VCR may have gotten into a bad (mechanical or electrical) state. 2. Unplug the VCR and remove the covers. Rotate the shafts of each of the motors (cassette loading and tape loading or main motors depending on your VCR) clockwise a couple of turns (assuming there is no resistance to turning). Plug it in and listen for initialization sounds - it should detect that the mechanism has been moved and then reset to a safe position. See if it is now behaving. 3. If (2) doesn't do anything, try several turns counterclockwise instead. 4. If still no improvement, there may be more serious power supply, motor, or control system problems. If any of these appears to solve the problem, it is quite possible that you will never experience it again. However, a dirty mode switch (see the section: @{"VCR mode (sensor) switches" link "10.3"} may have resulted in an overshoot to a bad mechanical state and without cleaning or replacement, the same thing may happen again. ----------------------------------------------------------------------------- @endnode @node 10.2 "Erratic behavior in various modes" You press PLAY and the VCR gets halfway through loading the tape and suddenly aborts and shuts down. Or, you put a cassette in and it is immediately spit out as though it tasted bad to the VCR. Or, you press PLAY and the VCR goes into REWIND mode. Or, you pressed REVIEW and it ejected or attempted to eject the cassette. Before you break out the screwdriver or shotgun, cover up the IR remote sensor and cassette slot. Some types of electronic ballasted fluorescent lights may confuse the remote control receiver. Or, someone or something may be sitting on the remote hand unit or it may be defective and continuously issuing a REW command! Excessive general illumination may even make its way into the tape start and/or end sensors and trick the VCR into thinking the tape is at one end. Assuming neither of these is the source of the problem: First, eliminate the possible mechanical causes such as slipping belts or a bad idler tire which could prevent the VCR from completing your requested action - it then shuts down or attempts to return to a 'safe' position. Bad connections are a possibility but not as likely as in a TV or monitor, for example. However, some VCRs (certain JVCs and clones, for example) ground parts of the circuitry via the circuit board mounting screws and simply tightening these are all that is needed to affect a cure. The microcomputer or its associated circuitry could be defective as well - but this is not as common most people fear. Occasionally, a faulty power supply may result in similar behavior. Its output voltages may be marginal, drop under load, or have excessive ripple due to dried up filter capacitors. However, a more likely possibility than any of the above is that a sensor assembly present on most VCRs called the 'Mode Switch' or 'Mode Sensor' is dirty or bad. See the section: @{"VCR mode (sensor) switches" link "10.3"} Failure of the Mode Switch is a very common problem with numerous VCRs of many makes and models. ----------------------------------------------------------------------------- @endnode @node 10.3 "VCR mode (sensor) switches" In order for the microcontroller in a VCR to confirm correct functioning and completion of various operations like cassette and tape loading and roller guide position, some mechanical sensor feedback is normally used. The most important sensor assembly in most VCRs is called the 'Mode Switch' or 'Mode Sensor'. The purpose of the Mode Switch is to inform the microcontroller of the gross position of the mechanism at all times. For example, the mode switch may have 5 positions: 1. Tape unloaded and cassette out. 2. Tape unloaded and cassette in. 3. Tape half loaded against A/C head but not around drum. 4. Tape fully loaded around drum and roller guides at V-stoppers. 5. Pinch roller pressed against capstan - play/record position. The microcomputer monitors the outputs of the Mode Switch continuously when it is executing a mechanical operation (some monitor it at all times even with power 'off'). If an operation takes too long to move from state to state or an incorrect state transition occurs, the operation will be aborted and an attempt - possibly several - will be made to return the transport to a 'safe' position - unloading the tape and possibly ejecting the cassette. If the Mode Switch contacts are dirty or worn, or if it has somehow loosened on its mountings and shifted slightly, one or more of these positions will report back incorrectly or erratically signaling an error condition. For example, a transition from state 1 to state 4 directly would totally confuse the poor controller. A Mode Switch that shifted out of place (or where other timing relationships in the VCR are messed up) might result in certain operations stopping at the wrong position as well. For example, if the Mode Switch shifts one way, the pinch roller may never quite press against the capstan or the roller guides may not snuggle up to the V-stoppers as they should in play mode. If it shifts the other way, operations may fail to complete and run against the mechanical stops - stripped or broken gears may even the result. Mode Switches are usually linear or rotary slide switches with 4 or more output terminals. They may or may not be easily accessible. On some, they are visible once the bottom cover is removed. On others, they are buried beneath a bunch of mechanical doohickies (technical term). Some are removable with a screw or two and a connector. Others require desoldering and the removal of a whole lot of stuff - all of which must be carefully replaced with exactly the same timing relationships - just to gain access. Once, you get at them, you can often snap apart the housing and use contact cleaner on the sliding contacts and surfaces. I usually do not use any kind of lubricant as it can gum up on the contact surfaces resulting in erratic outputs - possibly the cause of the original problems in the first place. Some may not come apart and replacement is the only option if squirting contact cleaner through any visible openings does not help. Sometimes, bad solder connections to the mode switch are the only problem. However, be very careful about not moving anything and take careful notes on the position of any parts that you disconnect as critical timing relationships are controlled by the gear positions. Stripped gears or other broken parts may result when the mechanism cycles. Also, in certain positions, levers or sliders operated by the mechanism you remove may spring out of position and you will need to make sure they get put back into the correct slots in any cams when you are done. Mark all gear positions even if they do not seem to be critical. See the section below on "How not to mess up your day my ignoring timing marks" or more simply: @{"Mechanical relationships in VCRs" link "10.4"} Note that if you experience erratic behavior with a VCR manufactured by Sharp, the probability of a dirty mode switch is very close to 1. ----------------------------------------------------------------------------- @endnode @node 10.4 "Mechanical relationships in VCRs" The complexity of the mechanism in a VCR can be quite intimidating. To avoid total frustration and really messing up your day, before you remove anything mechanical, take careful notes of precise relationships of any gear, lever, switch, anything that might possibly get back together in an ambiguous way. Often there are 'timing' marks on the gears just as you would find in a lawnmower or automobile engine. These will be little arrows or holes which will line up with stationary marks or with each other on adjacent gears when the mechanism is in a particular position. Often, it is best to put the mechanism in the position where the timing marks line up because there may be fewer levers, cams, etc. which are under pressure or tension in this position and thus fewer things to pop out at you. If there are no apparent timing marks, make your own with a scribe or pen. Sometimes mechanisms that at first appear not to be critical are obscured in such a way that they really control critical timing. So, when in doubt, make more notes than necessary - with diagrams. ----------------------------------------------------------------------------- @endnode @node 10.5 "VCR does not work after cassette was forcibly removed" You were watching your favorite tape and suddenly the VCR emits a mechanical eek and is now dead - or you press eject and the VCR shuts down without regurgitating your tape. Worse yet, someone (we will not point fingers) forcibly removed the tape to return it to the video store. Assuming that 'forcibly' does not mean that permanent damage was done, then the first place, as always, to check is the idler tire and then all other rubber belts. At this point it is hard to say whether your problem was compounded by the removal of the tape. If any gears were shifted with respect to one another, parts bent, or springs sprung, then without a service manual, it would be difficult for a technician let alone someone not familiar with your VCR to repair it. An error at power on usually means that the microcomputer thinks that it is unable to put the mechanism into a 'safe' position. This could be due to slipping belts, broken gears, a bad motor, shifted sensors, or faulty electronics. The original symptoms may have been a slipping idler preventing the takeup reel from rotating allowing tape to spill into the machine. Power on problems may be more serious. See the section on @{"VCR is failing the Power-up sequence" link "10.6"} ----------------------------------------------------------------------------- @endnode @node 10.6 "The VCR is failing the power-up sequence" This often means that the internal microcomputer found the mechanism in an unusual state and was unable to reset it. Some VCRs will actually move portions of the mechanism to make sure that everything is ok to accept a tape. Failure here may be the result of a slipping or broken belt or a belt that has popped off of its pulleys, gummed up lubrication, or some other mechanical fault. How old is it? Rubber parts tend to become smooth and lose their elastic properties ('rubberiness') after a few years. Does the VCR make any kind of whirring sounds before shutting down? This would mean that it is attempting to move something back into position. Is there a tape in the machine? How about a toy, peanut butter and jelly sandwich, or a little applesauce? It could be a sensor or other electronic problem, but check out the mechanical possibilities first. On a VCR which has been cleaned and with good rubber parts: VCRs have a light or LED (IR, infrared) in the middle of the mechanical assembly that detects the end of tape. When a tape is loaded the tape will cover the sensor. The controller can tell if the tape is at the beginning, middle, or end by the sensor. The is achieved by a clear leader at the beginning and end of the tape. The microcontroller will detect a problem if the sensors do not detect the light or LED (middle of tape) and the carriage assembly is up (no tape loaded). The VCR will shut down. 1. If you have an incandescent light and it is not lit, it is burned out. If you have the LED type you can buy an IR tester from an electronic parts supplier or construct one as described at the end of this document. Replacement LEDs are readily available. 2. The VCR might be in a confused state. Many VCRs have a belt that drives a loading motor. This is the motor that drives the tape around the heads. If those guides are not fully retracted, the VCR shuts down. Check the belt and replace if necessary. 3. Ensure the tape guide assembly is fully retracted by physically turning the appropriate gears. 4. Some obstruction is preventing part of the mechanism from resetting. Visually inspect for foreign objects or rough edges on something preventing full movement. Dried up grease can also cause this. 5. A gear has slipped a tooth and one part of the mechanism does not track another. This may happen if a tape was forcefully ejected after being eaten. You may find that a tooth has actually broken off. 6. If this occurred after having disassembled part of the mechanism, confirm the timing relationships. Make sure belts are installed in the correct locations - and on the correct sides of any intermediate pulleys where belts link more than two pulleys. Without a service manual, determining the correct relationships for all gears may be impossible, but if only one has slipped you may be able to locate timing marks near the edges of the gears which should line up - usually when the tape is unloaded. (portions from michael@marconi.nsc.com) ----------------------------------------------------------------------------- @endnode @node 10.7 "VCR displays DEW warning" Your VCR has worked fine for several years but now you get the 'DEW' warning in the display and no tape functions work. The dew sensor is intended to prevent operation of the tape transport if the humidity is so high that moisture would build up and cause the video tape to stick to the rotating drum and damage the heads or get hopeless tangled as a result. First, perhaps the dew warning is telling the truth. If you have just moved the VCR from a cold area to a warm one, let it sit for an hour or so and see if the dew warning goes away. If you just fished it out of the toilet or scraped stewed peaches from the interior, well, dew may be the least of your problems. Assuming that there is no reason for a dew warning, the dew sensor may be bad or have changed value. There may or may not be an adjustment for this. Before you go inside, try unplugging the VCR to clear any spontaneous fault condition - see the section on: @{"VCR goes whacko" link "10.10"} The dew sensor is a resistor that changes value when there is condensation. If the sensor is bad, you should be able to replace it with a resistor and keep the VCR happy. You should be able to determine the appropriate resistance by trial and error. If it is the type where the resistance decreases with moisture and the controller does not care if the resistance is too high, then you can just remove it. Either way, you have now lost the protection that the dew sensor provides. Replacement is obviously best. Don't overlook the possibility of a bad connection - it may be plugged in and just need to be reseated. One type looks like a ceramic board, maybe 1/4" - 1/2" on a side with a silver/gray printed circuit pattern. If the A/D or whatever is used to determine when there is dew is faulty, then you will most likely need a service manual to troubleshoot it. ----------------------------------------------------------------------------- @endnode @node 10.8 "VCR shows LOCKED in the display" You go and try to play a tape and the VCR displays the word 'LOCKED' or perhaps just a flashing 'L' in the display. This may mean that the VCR has somehow been programmed to prevent use by unauthorized kids (you are not reading this if you are a kid, right?) Even if your model does not have this feature, the same basic chassis is probably used for a range of models so it could have gotten into a confused state. o Sometimes, just pressing the PLAY (or other more obscure) button on the remote control (it may be designed not to work from the front panel) for 10-20 seconds will clear this mode. o Unplugging the VCR for a minute or two may work. Unplugging for long enough to drain the backup battery will probably work but you may then need to reinitialize the clock, channel selection, and programming. o Best bet is to check your instruction manual (you can locate your user manual, right???). ----------------------------------------------------------------------------- @endnode @node 10.9 "VCRs with Alzheimer's Disease" Suppose your just-out-warranty VCR is now acting up for no apparent reason - making strange sounds, forgetting its programming, refusing to cooperate, etc. I don't know what kind of recourse you may have as an unsatisfied consumer, but I would try to get some resolution through your place of purchase. Such a VCR has all the symptoms of Alzheimer's disease - it should not be failing in these ways so early in life unless it is under penalty of hard labor in the damp snake infested dungeon of an English castle! Or it has been the depository for peanut-butter-and-jelly sandwiches, applesauce, or marbles! All the usual recommendations of cleaning and checking rubber parts and so forth apply to units that have seen significant use or are a few years old or both. Something this new under normal use should not be causing this amount of grief. However, sometime I wonder whether using a machine very little contributes to problems. First try your place of purchase - there may still be some degree of interest in maintaining customer satisfaction. If you have given up on the store, start by checking the rubber parts for dust and deterioration (with that kind of use, dirt should not be a problem, but dust or smoke can accumulate), check for adequate lubrication (but don't add any unless it is definitely needed and then only the smallest amount - VCRs do not need much oil or grease and too much will just compound your problems - and check for foreign objects especially if there are small kids about. ----------------------------------------------------------------------------- @endnode @node 10.10 "VCR has gone whacko" You may think you are on the set of the latest sci-fi movie. The VCR displays are counting at random, pushing buttons produce unexpected results, motors may be spinning, or the VCR may be repeatedly loading and unloading a non-existent tape. I may be attempting to play a tape even without you pressing any buttons. While these could be symptoms of a actual problem, first try unplugging the VCR from the wall outlet (don't just turn it off) for a minute or so. If this does not help, try unplugging for a couple of hours - this will usually drain the backup battery and reset many other functions of the VCR. If one of these techniques results in the universe returning to normal, there may have been a power surge or lightening strike nearby which threw the microcontroller into a confused state. It may never happen again. However, power surges can be the result of heavy appliances like air conditioners on the same circuit. If this is the case, you should consider using a different circuit for your electronic equipment. If this behavior started when the VCR was just plugged in or following some other action requiring the mechanism to move or initialize, check for mechanical problems like a broken belt or one that has popped off its pulleys or an obstruction like a rock or toy that is preventing the VCR from completing the required motions. Also see the section: @{"VCR is failing the power-up sequence" link "10.6"} Once you have ruled out mechanical problems, it is likely that the VCR has a microcontroller, power supply, or other electronic problem which may require professional service. ----------------------------------------------------------------------------- @endnode @node 10.11 "VCR forgets settings following power failure" Normally, the AC line provides power to retain the clock, active channels, and programming settings. During a power failure, the clock and programming is usually powered using a supercap or battery (usually rechargeable). Channel settings for older style varactor type tuners were often stored in some kind of non-volatile memory while active channels for quartz tuners generally use battery backup. The clock and programming backup may be a supercap - a very high value special electrolytic capacitor - as much a 1 F (1,000,000 uF) at 5-12 V. Alternatively, it may use a rechargeable NiCd battery. In either case, these are easily replaceable with standard parts. A NiCd battery pack of similar ratings should be readily available. Supercaps are available from large electronics distributors. NiCd batteries fail in two ways - loss of capacity or shorted cells. If memory is retained for a much shorter time than it used to, then the battery has probably lost most of its capacity. If you measure less than n x 1.2 V for an n cell NiCd battery pack after it has been charging for awhile, there is likely a shorted cell. In either case, the best solution is a replacement though the various common techniques for rejuvenating NiCd battery packs can be attempted (remove from VCR first!). The non-volatile memory could use a special chip like EEPROM which does not require power or a battery backed SRAM or be internal to one of the VCR's microcontrollers. Channel memory may use a separate power source from the clock and programming, possibly a Lithium battery since it is undesirable for the channel settings to be forgotten even if the VCR is unplugged for a month or more as it is such a pain to reinitialize them. Rechargeable batteries have too high a self discharge rate. ----------------------------------------------------------------------------- @endnode @node 11.1 "VCR randomly switches speeds, tracking problems, and muddy sound" First, don't ignore the possibility that you are attempting to play an old, worn, or defective tape. This is especially true of rental tapes which have been through who knows what kind of VCR hell. The control and audio tracks - along the edges of the tape - are the first to wear. Weak muddy sound and erratic tracking are also common symptoms caused by old worn tapes. Assuming you are having the same problem on multiple tapes: This is an indication that your tape path alignment is off or your rubber parts (probably the pinch roller) need replacing. The tape is wandering up and down as a result of unequal pull from the capstan due to a glazed/worn pinch roller. There could also be other aspects of tape path alignment like roller guide tilt (which is probably not adjustable), A/C head tilt, dirt, roller guide height (don't mess with it), etc. See the section on @{"tape path alignment" link "19"} It could also be worn feet on the roller guide assemblies causing the guides to not be perfectly vertical - replacement of these parts may be the only cure. Other much less likely possibilities: excessive or varying backtension, tight idler clutch, electronic problems. Another related symptom is that the sound does not always appear at full volume or normal quality for a few seconds after the VCR starts playing. It may vary in loudness during play as well. Slightly changing backtension may make a big difference in audio. If you look carefully, you should be able to see the tape wandering slightly producing the muddy sound and erratic tracking. The tape may not be perfectly smooth in passing over the various guides and rollers. Normally, you will almost not be able to tell the tape is moving at all except by examining the reel rotation - it is that mirror smooth. First, clean the tape path properly, especially the capstan and pinch roller, tape guides, A/C head. Inspect the pinch roller for glazing, cracking, etc. and replace if necessary. See the sections on @{"cleaning" link "6.3"} and @{"tape path alignment" link "19"} ----------------------------------------------------------------------------- @endnode @node 11.2 "VCR plays but at fast forward speed (or beyond)" Normally, speed is controlled via phase locking the capstan to the (approx.) 30 Hz control pulses read off of the tape via the stationary audio/control head. Possible causes for loss of lock: 1. Dirt or bits of tape or oxide on control head - clean and inspect. 2. Defective control head. Try making a recording. If recording plays normally on another VCR, then control head is probably ok. 3. Tape wandering up and down so that control track is not sensed properly (how is the sound - this would also cause fluctuating or missing sound.) See the section @{"VCR randomly switches speeds, tracking problems, and muddy sound" link "11.1"} 4. Mechanical fault preventing firm tape-control head contact such as a stuck movable guide post. 5. Mechanical or mode switch problem preventing firm capstan-pinch roller contact. Under certain conditions - possibly at the beginning of a tape when takeup tension is greatest - the takeup reel may have enough torque to pull the tape past the video heads without the capstan controlling the speed as it should. 6. Defect in servo or control circuitry or power supply (voltage out of tolerance). 7. Bad tape. Don't overlook this possibility especially if it is a old or rental tape. The control track may have gotten erased or warn off - it is at the edge of the tape. Try another tape. Inspect the tape path really really carefully to determine if there is some obstruction preventing tape-control head contact or other mechanical problems. Try cleaning the tape path and checking the rubber parts. Check power supply voltages if you can determine what they should be (see the section on @{"VCR power supplies" link "15.3"} If these procedures to not reveal anything amiss, you will need a service manual to pursue electronic faults. ----------------------------------------------------------------------------- @endnode @node 11.3 "Tape edge gets creased and/or random switching between speeds" As always, rule out the possibility that this is just a bad tape. It could have been creased by someone else's VCR. Try a tape you can afford to sacrifice (though it will still be safely usable) and run it through the VCR. Sometimes, there will be a problem only near one end so you will need to try it at various sections of tape. Record a few minutes and then back it up a bit and inspect for damage by opening the cassette door (press the release on the side). Both edges should be perfectly flat and smooth. If you get similar playback symptoms with this cassette and/or find that the tape is being creased along one or both edges, then it is your VCR doing the dirty work. When the bottom of the tape gets creased, the control head may no longer align with the control track and you loose servo lock on the sync signal. Your audio may be fluctuating in intensity as well since the audio track is wandering also and the tape may be intermittently going in and out of correct tracking and/or changing speeds. It could be the guide posts or other tape path components, but before you turn every screw you can find and make the problems hopelessly worse, replace all of the rubber parts - belts, idler tire, pinch roller. And while you are at it, give the machine a good cleaning. If you want to do this before buying the new rubber (which BTW should not be more than a total $10-$15 from a place like MCM Electronics), you may at least see a temporary improvement in performance. You really need to determine exactly where the tape is being creased. Once you do this, you may be able to determine the cause and visually verify whether the problem is affected by any of your adjustments or probing. Some possibilities are: o Worn feet on the roller guides causing them to not be precisely vertical. Sometimes there are adjustments for tilt; usually there are none. Sometimes replacements are readily available (especially if this is a common problem with your model). o Cassette not seating properly. Press down on cassette while playing a known good tape. If it moves, then check for obstructions or foreign objects such as toys or peanut butter and jelly sandwiches! A dirty, oily, or just tired belt may not grip well enough for the mechanism to complete the cassette load cycle. o Various guides too high or too low but this is pretty unlikely unless they have loosened somehow. Don't adjust unless you have a service manual or are absolutely sure that they have changed height. o Backtension misadjusted. If the tape passes around the backtension lever at too straight an angle (it doesn't bend enough), in addition to the possible incorrect backtension, it may simply not seat properly when passing around the subsequent guidepost or impedance roller. ----------------------------------------------------------------------------- @endnode @node 11.4 "Recording stops at random times on previously used tapes" Symptoms may be that the tape counter stops moving and/or the VCR enters stop mode and shuts down. Assuming this is not a mechanical problem - bad idler, belt, etc., make sure you don't accidentally have an 'insert editing' mode enabled. Insert editing uses the previously laid down control track as the timing reference. This provides clean glitch-free transitions between scenes. Insert editing will not work at all on a new or bulk erased tape. If you routinely use your cassettes over and over, there will be varying amounts of previously recorded material - with control tracks - on the tapes. At some point your recording may start to use tape beyond the recorded sections and - presto, no more control track. Poor VCR is confused and aborts. ----------------------------------------------------------------------------- @endnode @node 11.5 "Record (or play) stops after 15 minutes (or 30 minutes, etc.)" Make sure you are using the proper record button. Most VCRs have a OTR (One Time Record) or 'quick record' feature which starts just like normal record stops after a multiple of (usually) 15 minutes depending on how many times you press the button. The (normally) red button should be used for unrestricted untimed recordings. Some VCRs also have other timed modes - sort of like the timed off function of a clock radio. Pressing the 'Off-T' button adds time to record or play in 15 minute increments and then the VCR shuts off. ----------------------------------------------------------------------------- @endnode @node 12.1 "Video playback problems" If the VCR works in all respects when tuning broadcast or cable channels but playing a tape results in no picture, a very snowy picture, or just a blue screen, there may be problems with the video heads, the lower cylinder, head preamps, or other video electronics. Testing most of these is beyond the scope of this document and will require a service manual and test equipment. However, you can do a decent job of determining if the video heads are likely to be at fault. ----------------------------------------------------------------------------- @endnode @node 12.2 "Video record problems" If attempting to record results in unexpected behavior, there could be a variety of causes depending on what you get for playback: o Attempts to record are ignored by the VCR or cause the cassette to be ejected. This may mean the the record protect tab on the cassette is broken off or the record tab sense switch is dirty or bad. o Playback results in video snow. This means that the old recording is being erased (if there was one) but nothing or too weak a signal is being written by the video heads. This could be dues a variety of electronic faults as well as marginal or bad video heads. o Playback results in a picture but it has a wiggling rainbow pattern running through it. This is normal at the start of a recording made on top of an old recording if your VCR does not have a flying erase head. However, it should wipe down the screen in a few seconds and disappear. If it does not, then your full width erase head is not working. o Playback results in a flickering picture alternating between good video and snow at the frame rate (about 30 Hz for NTSC). This could mean that one of the heads used for record is dirty or defective. o Playback results in proper video but the previously recorded or no audio. The audio dub switch (if any) may be in the wrong position or the audio circuitry may be defective. ----------------------------------------------------------------------------- @endnode @node 12.3 "Snow on one or more speeds" Did the problem happen suddenly? Or develop over time? If suddenly, what were you watching at the time? A (literally) dirty rental movie? If this VCR has 4 or more heads, SP and EP may use a different set of heads, so certain heads may still be dirty or bad. If the machine tracks perfectly in EP, then alignment is probably fine - EP is more critical as to alignment as the EP track is 1/3 the width of the SP track. Have the video heads been cleaned using the proper procedure (not just a cleaning tape - see section on @{"video head cleaning" link "18.4"} New video heads may fix this, though it can be caused by other problems such as weak read electronics. See the section on @{"video head problems" link "18"} You should also check the backtension adjustment - if too loose, head to tape contact will be compromised. Try increasing it momentarily by pushing the backtension lever slightly to the left while the tape is playing. The usual way to adjust backtension without a backtension meter and service manual is to look at the image just before vertical retrace at the bottom of the screen - this is normally not visible unless you can reduce vertical size or play with vertical hold to get the vertical blanking bar to appear. Of course, most modern TVs don't have any such controls! This is the head switching point and when the backtension is properly set the image above and the bit of image below this break will be approximately aligned. If increasing backtension helps, either the heads are marginal or the backtension was low. However, low backtension will usually show up as a waving or flagging effect at the top of the picture. ----------------------------------------------------------------------------- @endnode @node 12.4 "Jumpy picture in play" You have a VCR with known good heads that produces jumpy (vertically) video in play that cannot be stabilized with the tracking control. Perhaps you have attempted to adjust the mechanical tracking and maybe some other stuff. Some questions: o Did you replace the heads? Could you have gotten them 180 degree rotated from the correct position? I don't know what the implications would be on your model VCR, but there is a definite right and wrong on this. It would certainly show up as tracking being way out when attempting to play back tapes recorded on this VCR on another machine. o Exactly what adjustments did you touch? o Have you verified that the roller guides are fully engaged against the stops? o Have you checked backtension? o Did you touch roller guide height? This is probably a mechanical problem, most likely an adjustment or fault related to tape path alignment. However, it could also be due to electronic problems with the video or servo circuitry. The vertical sync could be corrupted or the head switching point not set correctly. The head switching point is 6.5 lines before vertical sync. If this ends up moving into vertical sync for some reason, you will get unstable video. The supply side roller guide height adjustment is also critical and would be the first thing to check mechanical alignment problems are suspected. However, don't overlook the obvious: Your TV is marginal or misadjusted or you are attempting to play a bad tape. ----------------------------------------------------------------------------- @endnode @node 12.5 "Incorrect frame alignment or bad video for part of frame" Symptoms like a picture which has a portion that is noisy or missing, or where the picture is split between top and bottom with the vertical blanking somewhere in between may indicate a problem with the PG sensor. The rotational position reference for the video head drum is usually supplied by a pickup in close proximity to the edge of the lower cylinder (probably) which has a small magnet fastened to it. This generates the so called 'PG' pulse and is used by the servo circuitry to properly control the drum rotation and the head switching point. If this sensor is moved or if there is a fault in the PG circuitry, a variety of record or playback problems can result. Without this reference, the servo circuitry has no way of knowing where the A and B heads are at any given time. During record, this may result in recording video which is not properly lined up with the video tape - a track may consist of the end of one field and the beginning of the next rather than an entier fields as it should. During playback, the head switching point may occur at the wrong time resulting in a partially snowy or missing picture since a head that is not even in contact with the tape may be active. Similar problems may make look like your TV's vertical hold control is set incorrectly with the vertical blanking bar visible at an arbitrary point on the screen. Beyond confirming that the pickup coil is in close proximity to the drum and that there are no bad connections or loose connectors, there is not much to be done for these problems without a service manual. The definitions below are just FYI: PG - pulse generator. The pulse is derived from the rotation of a magnet on the video head drum past a sensing coil. I suppose this could be done optically as well. FG - frequency generator. This is a signal (sine or square) derived from the rotation of the video head drum. This may be phase locked to the PG pulse but can be a multiple of the frame rate. This could also refer to the capstan or reel rotation rather than the head drum. ----------------------------------------------------------------------------- @endnode @node 12.6 "Rainbow pattern in recordings made over previously recorded tapes" Unless your VCR has a flying erase head - located along with the normal video heads on the rotating drum - you will see a faint rainbow pattern near the start when recording over a previously used tape. The reason is that there is a separation of a few inches in the tape path between the video heads and the full width erase head. When you start recording at an arbitrary point, it takes several seconds (actual time depends on recording speed) totally erased tape to make it to the video heads. You are seeing an interference pattern between the old and new video signals. The pattern will slowly wipe from top to bottom as the diagonal tracks of new video intersect more and more of the erased tape. This effect will not occur (except possibly at the very beginning of the tape) as long as you record from start to end without backing up the tape at any time. If the rainbow pattern is present whenever recording over previously recorded tapes and does not go away, then your full width erase head is not working. This could be due to an electronic failure or simply a bad connection to the full width erase head. Alternatively, a mechanical problem such as a broken or popped spring or gummed up lubrication might prevent the pivoting full width erase head from contacting the tape properly. ----------------------------------------------------------------------------- @endnode @node 12.7 "Flag waving" You have just loaded a videotape sent to you from your long lost cousin and you notice that the top of the picture is wiggling back and forth. First, if this wasn't the original complaint, make sure the flag waving problem exists with the TV that will actually be used with the VCR - it may just be your test TV or monitor that is unhappy. (Parts of the following from: Andrew Morphitis, Andrew@andrewsm.demon.co.uk). This fault is sometimes known as flag-waving when associated with video recorders. If the tape back-tension provided by the tension arm and supply reel-table is not the same as the back-tension provided when the tape was recorded (possibly on another machine) then the field timing of the video tracks being played back will be inconsistent . Your back- tension can be checked using a back-tension cassette gauge (a typical reading would be about 35g-cm for VHS) or you could adjust the back tension using a known good test tape (or reliable pre-recorded tape) until the waving disappears. If your back-tension does turn out to be incorrect and you adjust it according to the manufacturers spec. then all of the tapes you have previously recorded will probably still exhibit this waving problem - adjust to spec. or to your tape library - take your pick. Thats the theory - now the practice. Back-tension refers to the tension of the tape over the head drum, this is provided by the felt covered metal band (tension band) which is wrapped around the supply reel (left-hand reel from the front), the friction providing the tension. There are usually two adjustments associated with back tension and these can be found near the opposite ends of of this tension band, the tension arm operating position and the anchor point of the band. Adjusting the latter position will increase or decrease back tension (you will want to increase your back tension which has dropped due to excessive wear on the belt). If you do give it a bash then be aware that poorly adjusted back-tension can, at worst, give rise to premature head wear. Because of the differences between the back tensions of different machines, all modern TV's have a dedicated video channel button (usually channel 0) which has a shorter flywheel line-timing duration allowing the TV timebase to lock up more effectively to unstable video sources such as video machines. Are you using the video channel? - try playing the video through different channels on your TV. ----------------------------------------------------------------------------- @endnode @node 13.1 "Poor quality sound on non-HiFi VCR" There can be several non-electronic causes: 1. The audio head needs to be cleaned. A cleaning tape may not be effective. You can use Q-tips and medicinal or pure isopropyl alcohol or tape head cleaning solution. You might as well clean the tape guides as well while you are at it - a speck of dirt can cause the tape to wander and produce erratic sound. 2. The audio/control head needs to be aligned - particularly the azimith adjustment which is the angle the head gap makes with respect to the direction of the tape's long axis (I hope this is clear). You can do this if you are so inclined. Before you adjust azimith, a test for this would be to record and then play back a tape on this machine - regardless of how far off the azimith adjustment is, the recording should sound good (at least as good as one can expect from the linear audio) track. See the section on @{"Tape path alignment" link "19"} 3. The audio head (and other parts) needs to be demagnetized - use an audio tape head demagnetizer. Stay away from the video heads. Some demagnetizers are powerful enough to damage them. Make sure the demagnetizer you use has a no sharp ends to damage anything - cover with electrical tape if in doubt. Turn on the demagnetizer and move it slowly near all metallic parts that the tape contacts - guides, levers, erase and audio/control head. As mentioned, do not go near the video heads. See the section on @{"Head demagnetizing" link "6.5"} 4. The audio head is worn. If the poor sounds quality really bugs you, these can be easily replaced but they are not cheap since generic replacements are rarely available. Alignment will then be needed. 5. Tape path problem causing bad tape-head contact. See section on @{"Tape path alignment" link "19"} 6. Your expectations for audio quality on the linear audio tracks on a non-HiFi VCR are unrealistic. The worst will be a stereo VCR in EP mode since the stereo tracks are less than half as wide as non-stereo tracks. Best will be SP non-stereo but even this is very poor for music. Once you get used to HiFi quality, linear audio sounds like crud. ----------------------------------------------------------------------------- @endnode @node 13.2 "Excessive flutter on VHS linear audio playback" While general quality of VHS linear audio is almost always mediocre, there should not be excessive flutter - wavering in pitch. Certainly it should not be noticeable for speech. How bad music sounds will depend on your expectations as well. Here are some possible causes: o Dirty/gummed up stationary guides or A/C head. o Lack of lubrication of the capstan or roller guides. o Excessively tight idler or other clutch. o Bad capstan motor, especially if direct drive type, or motor driver. o Servo system problems. o Power supply problems. o Stiction between tape and lower cylinder. o Unrealistic expectations of linear audio quality. Some VCRs are downright terrible, especially at EP speed. This is normal. ----------------------------------------------------------------------------- @endnode @node 13.3 "Previous (non-HiFi) audio is not erased on new recordings" If the old audio track is unchanged - you get the new video but old audio, check that any dubbing switches are set correctly - to enable audio. If you are getting a mixture of old and new audio, then there could be a problem with the audio erase head (part of the A/C head stack) or its circuitry. Clean the audio/control head (the stationary head to the right of the video drum near where the tape re-enters the cassette. Check for dirt or tape oxide on or around the audio/control head. Beyond this, testing will probably require a schematic. However, if you can locate the connections to the audio erase head, use an ohmmeter to test for continuity of the coil. Check with an oscilloscope for the high frequency erase signal during record. ----------------------------------------------------------------------------- @endnode @node 13.4 "Poor quality sound on HiFi VCR" The VCR may be switching between HiFi and linear audio at random (with the HiFi light also flickering on and off or simply not selecting HiFi audio at all. The sound out of a HiFi (not just stereo) VCR should be virtually indistinguishable from the original and for good quality source material, nearly as good as a CD. What to look for if it is really playing HiFi (try at slowest tape speed as this will have little effect on HiFi quality but will turn the linear track quality to crud). Use a tape with a musical recording for this: o Almost no tape hiss (background should be virtually silent). o Excellent frequency response (treble notes should sound natural). o Excellent dynamic range (loud louds and soft softs). o No detectable wow or flutter (no short or long term wavering in pitch). Since the HiFi heads are on the rotating video head cylinder, they are subject to the same problems as video heads - and the same difficulties in diagnosing head problems. Dirt, damage, or electronic defects can cause the HiFi sound to be absent or distorted. A broken or badly worn HiFi head will simply cause the VCR to switch to the linear audio tracks. HiFi head alignment is more critical than video head alignment so this may need to be checked. Try adjusting the manual video tracking control as this will also affect HiFi audio tracking and see if this clear up the sound. ----------------------------------------------------------------------------- @endnode @node 13.5 "Squealing noise from VCR in certain modes" Unusual noises from inside the VCR may be an indication of a problem or just a badly made cassette - try a different one. The most common cause for a squealing noise are tired weak belts that are slipping. Less likely is the need for lubrication. o A squeal when entering play or record mode - with the VCR perhaps aborting the operation - is usually caused by a slipping loading belt. o A squeal during fast FF or REW may indicate a slipping drive belt. o A squeal or whine during play or record (perhaps intermittently when the video head drum is spinning) could be a worn video head drum bearing or dirty or improperly positioned static brush (see also: "High pitched whine from inside VCR"). See the appropriate sections on @{"cleaning, rubber parts" link "6.3"} and @{"lubrication" link "6.4"} o A whine from the audio (of the TV) while using the VCR may indicate bad grounding of the internal shields, other bad connections, or electronic problems. ----------------------------------------------------------------------------- @endnode @node 13.6 "High pitched whine from inside VCR" Your first thought is probably of an expensive repair to a motor bearing or replacement lower cylinder. If there is a high pitched whine coming from inside the VCR when in PLAY, REC, or other mode which spins the video heads, you may simply have a dirty or mispositioned antistatic brush. There is usually a metal strip with a carbon contact pressing against the center of the video drum spindle either above or below the deck. It is very common for it to vibrate is just the right way to sound like a cat being strangled. Gently press on this strip or lift it off of the spindle while you hear the sound. If the whine disappears, cleaning and slight repositioning of the strip should be all you need to do. Do not remove this strip - it is needed to ground the rotating drum to prevent static buildup and video noise problems (see the section on: @{"Firing (static) lines in picture during playback" link "14.5"} ----------------------------------------------------------------------------- @endnode @node 14.1 "VCR color problems" There are two typical situations: o Playback is always in B/W. o Record is B/W but playback has normal color. If you can play prerecorded tapes in color but tapes recorded on this VCR do not play back in color, there may be several possible causes. The simplest is that your input signal is too weak - a misadjusted antenna or cable with a large number of splitters - and the VCR's color killer thinks there is no color. Sometimes the threshold for detecting the color signal is set higher on the VCR than the TV which you are using to monitor the recording. Some questions: o Is the color TV's fine tuning set correctly? o Does it play prerecorded tapes in color? o Does the tuner output produce color? o Does the video output work in color? o Is the problem the same for all recording speeds? o Do the tapes you record on this VCR play in color on another one? If the answer to all but the last question is 'yes', then the problem is most likely in the video/chroma circuitry associated with recording function. It could be as simple as the color killer setting being too low. Possible sources of problems with color recording: 1. Weak signal - check and/or adjust antenna. 2. Color Killer set to low. 3. Problems in tuner - does the video output work in color from the tuner? 4. Problems in chroma circuits. 5. Sometimes, marginal heads - less likely if it plays in color. If recording works fine as indicated by tapes made on this VCR playing fine on another one but prerecorded tapes do not play back in color and the VCR works fine in all other respects there could be several possible causes: 1. Weak chroma signal level from VCR. 2. Color Killer set to low on TV. 3. Problems in chroma circuits. 4. Marginal or dirty video heads. Note that in all cases of missing color, checking with another TV and/or adjusting the TV's controls should be tried first as slight differences in signal levels between tuner and playback may cause a TV with marginal settings (fine tuning, color killer, chroma circuits) to switch unexpectedly between color and B/W. ----------------------------------------------------------------------------- @endnode @node 14.2 "RF signal problems" First determine whether there is a problem with broadcast or cable, playing tapes, or both. If it is only broadcast or cable, then your source may be at fault. If it is fine with the VCR off but noisy when using its tuner, the problem could be in the tuner itself. Verify that the direct video output (RCA jacks) works properly with a prerecorded tape. If this is noisy as well, then there are problems with the video circuitry or video heads. If there are problems with the Channel 3/4 output but the direct video outputs are fine, then suspect a weak or dead RF modulator. This is a little metal metal box with the Antenna In and TV Out connectors. It has circuitry which switches between the VCR's internal video signal and the antenna input. It also converts the video baseband signal to the channel 3/4 output required by the TV. Before you conclude that the RF modulator is to blame, check that the channel and fine tuning of the TV are properly set and that there are no other problems with the TV. Test the VCR with another TV. It could be that the signal from the VCR is just a little weaker than it is used to be. Try moving the channel 3/4 switch back an forth - it may have developed a bad contact. Try the other channel (3 or 4) - it may work better. Try moving the VCR away from the TV - sometimes interference from the TV will degrade the video quality. If you do conclude that the RF modulator is at fault, generic replacements are available from the parts sources listed near the end of this document or other electronics distributors for less than $25. Replacement is straightforward since there are only a couple of soldered connections but getting to the unit physically is sometimes a challenge. ----------------------------------------------------------------------------- @endnode @node 14.3 "VCR will not tune broadcast or cable" Are you sure that the input signal is making to the VCR? Does the pass- through connection work? Double check the connections. Connect the cable you have on the ANTENNA IN of the VCR directly to the TV. Make sure it's center pin is not bent over or broken off. Try a new cable. Is the tuning mode switch (broadcast, CATV, etc.) set correctly on the VCR? If the signal is preset into the VCR, there still may be a bad connection inside preventing it from making it to the VCR's tuner. Sometimes, there are RCA style plugs inside that work loose. Otherwise, the tuner of the VCR is not working. This could be because it is broken or power to it is bad or missing. If all other functions of the VCR are working, it is likely (though not guaranteed) that the power supply is fine. There could be bad connections or dirty connectors as well. Beyond probing for bad connections and verifying your antenna hookup, there is not much that can be done without a service manual and test equipment. ----------------------------------------------------------------------------- @endnode @node 14.4 "Interference as parallel horizontal lines when playing tape" o Determine if it in the video signal or is it only present when the VCR is close to or sitting on/under the TV? o Does it happen when watching from the antenna/cable but a tape is playing or recording? o Have you rearranged your setup recently? It is common for TVs and VCRs to interfere with each other's operation. o Did this just start suddenly? o Is the quality of the video otherwise good? o Does it matter what tape speed is used? o Does it also occur during record? Some model VCRs just do not want to be close to other equipment like TVs. Your only easy fix may be to shuffle the components in your entertainment center. ----------------------------------------------------------------------------- @endnode @node 14.5 "Firing (static) lines in picture during playback" These may be described as static or short bright or dark lines in the picture. They usually have a sharp start and may trail off or stop abruptly. They may be occasional (once every few seconds) or frequent (multiple instances per video frame). Also see the sections on @{"video head problems" link "18"} as large quantities of firing lines may be due to dirty, worn, or defective video heads. First, try a different tape - preferably a new recording made on a different VCR or a new commercial video. It is possible that these streaks are simply due to dropouts on the tape - missing bits of oxide or dirt causing momentary loss of video signal. Old, worn, or cheap off-brand tapes are particularly prone to dropouts. One characteristic of dropouts is that they may span video lines as well as video frames. If your lines are very short and random, they may be caused by a dirty, missing, or improperly positioned video drum static brush. In most VCRs, you will see a metal strip with a carbon contact pressing against the center of the video drum spindle either above or below the deck. It is there to provide electrical contact between the rotating video drum and the stationary lower cylinder and chassis. This is necessary since the bearings on which the upper cylinder rotate may not provide adequate contact and any static buildup caused by the spinning head cylinder rubbing against the tape may discharge through the bearings resulting in these firing lines. Carefully remove the static brush and clean the end of the spindle and carbon contact. This may be all you need to do to remove the static lines from your picture. ----------------------------------------------------------------------------- @endnode @node 15.1 "Multiple system problems" Most VCR problems will be limited to a specific subsystem - video, audio, tuner, servo, control. When multiple seemingly unrelated problems occur at the same time, suspect a power supply problem since multiple systems may be fed from common power supply outputs. There are always several different voltages used within a VCR - if one of these dies, some subsystems will work but will not receive the proper signals from the dead parts. So, nearly any kind of behavior is possible. Therefore, the first test is to determine, if possible, that the power supply outputs voltages are correct - both with power off and power on. ----------------------------------------------------------------------------- @endnode @node 15.2 "Power supply problems - unit totally dead/major system problems in all modes" Power supply problems can range from intermittent behavior due to slightly out of tolerance voltages, hum, or noise to a totally dead VCR. Multiple system failures can result if one or more of the half dozen or so voltages used within the VCR are incorrect or missing. Some power supply problems are caused by power surges. These may result in a totally dead VCR or in overstress and subsequent failure of various components. A power strip with a circuit breaker, even with surge protector is not a reliable protection against power surges especially during lightening storms. The only sure protection is unplugging electronic equipment during storms - but then, what would your insurance agent have to do? ----------------------------------------------------------------------------- @endnode @node 15.3 "VCR power supplies" Reread Safety info before tackling any power supply problem in a VCR! VCRs typically use one of four types of power supplies (There are no doubt others): 1. Power transformer with linear regulator using 78/79XX parts or discrete components. The power transformer will be large and very near the AC line cord. 2. Power transformer with hybrid regulator like STK5481 or any of its cousins - multioutput with some outputs switched by power on. If it has one of these, check ECG, SK, or NTE, or post to sci.electronics.repair and someone can probably provide the pinout. Again, the power transformer will be large and very near the AC line cord. 3. Small switching power supply. Most common problems: shorted semiconductors, bad capacitors, open fusable resistors. In this case there is usually no large power transformer near the line input but a smaller transformer amidships. 4. Combo of the previous - these are less common. An input power transformer may supply low voltage to a switcher. 5. Camcorders and portable video camera-VCR combos include a battery charger and run all normal VCR (and camera) functions off of the battery. The required voltages are derived using DC-DC invertors. Here are some general comments for each type: 1. Troubleshooting is quite straightforward as the components are readily identified and it is easy to trace through from the power transformer, bridge or centertapped full wave rectifiers, regulators, caps, etc. The circuitry is not usually complex and the most common failures tend to be quite obvious. 2. Failures of one or more of the outputs of these hybrid regulator blocks are very common. Use ECG/STK/NTE cross reference to identify the correct output voltages. Test with power switch in both positions. Any significant discrepancy indicates a likely problem. While an excessive load dragging down a voltage is possible, the regulator is the first suspect. Replacement cost is usually under $10. 3. Switching supply problems are tougher to diagnose but it is usually possible without service literature by tracing the circuit and checking for bad semiconductors with an ohmmeter. Common problems - dried up capacitors, shorted semiconductors, and bad solder joints. In a supply that is dead - has blown the main fuse - check ALL semiconductors, capacitors, and resistors as a failure in one may damage others and just replacing the first one you find that is bad may result in it just blowing immediately. Fusable (flameproof) resistors (blue or brown body or boxy ceramic power type) may open up if there was a shorted switching transistor. Power resistors supplying current for the startup circuit may open from age. See 'Notes on Diagnosis and Repair of Small Switchmode Power Supplies' for more detailed information. 4. Problems in either the power transformer/rectifier/filter capacitor section (usually no regulator) or switching supply are possible. However, they can pretty much be dealt with independently. Note: the switching supplies used in these usually run off of a lower voltage input than the more common off-line non-isolated type making them somewhat less hazardous to your health to work on. 5. Problems can occur in either the battery charger or power supply section. Short running time on battery alone is usually caused by a bad battery. If possible, try a known good battery or battery eliminator first to determine which it is. The older style portable units were quite reliable and easy to service. However, modern camcorders are so jam packed with microminiature surface mount unmarked circuitry that troubleshooting and repair is definitely not fun. Not to mention the joys of just getting inside with only a finite use of expletives. Don't overlook the possibility of bad solder connections as well. ----------------------------------------------------------------------------- @endnode @node 15.4 "Internal fuse blew during lightening storm (or elephant hit power pole)" Power surges or nearby lightening strikes can destroy electronic equipment. However, most of the time, damage is minimal or at least easily repaired. With a direct hit, you may not recognize what is left of it! Ideally, electronic equipment should be unplugged (both AC line and phone line!) during electrical storms if possible. Modern TVs, VCRs, microwave ovens, and even stereo equipment is particularly susceptible to lightening and surge damage because some parts of the circuitry are always alive and therefore have a connection to the AC line. Telephones, modems, and faxes are directly connected to the phone lines. Better designs include filtering and surge suppression components built in. With a near-miss, the only thing that may happen is for the internal fuse to blow or for the microcontroller to go bonkers and just require power cycling. There is no possible protection against a direct strike. Most VCRs have their own internal surge protection devices like MOVs (Metal Oxide Varistors) after the fuse. So it is possible that all that is wrong is that the line fuse has blown. Remove the case (Unplug it first!) and start at the line cord. If you find a blown fuse, remove it and measure across the in-board side of fuse holder and the other (should be the neutral) side of the line. With the power switch off, this reading should be very high. With the switch on, it may be quite low if the VCR uses a large power transformer - a typical primary resistance is 15 to 30 ohms. Some VCRs may be outside this range but if the reading is extremely low, the power transformer could have a partially or totally shorted primary. If it is very high (greater than 1 K ohms), then the primary of the power transformer may be open or there may be blown thermal fuse under the insulation wrappings of the transformer windings. If the VCR has a switching power supply, see the document: "Notes on the Diagnosis and Repair of small SwitchMode Power Supplies (SMPS)". If the resistance checks out, replace the fuse and try powering the unit. There will be 3 possibilities: 1. It will work fine, problem solved. 2. It will immediately blow the fuse. This means there is at least one component shorted - possibilities include an MOV, line filter capacitor, transformer primary. 3. It will not work properly or still appear dead. This could mean there are blown fuses or fusable resistors or other defective parts in the power supply or other circuitry. In this case further testing will be needed and at some point you may require the schematic. ----------------------------------------------------------------------------- @endnode @node 15.5 "Use of surge suppressors and line filters" Should you always use a surge suppressor outlet strip or line circuit? Sure, it shouldn't hurt. Just don't depend on these to provide protection under all circumstances. Some are better than others and the marketing blurb is at best of little help in making an informed selection. Product literature - unless it is backed up by testing from a reputable lab - is usually pretty useless and often confusing. Line filters can also be useful if power in you area is noisy or prone to spikes or dips. However, keep in mind that most well designed electronic equipment already includes both surge suppressors like MOVs as well as L-C line filters. More is not necessarily better but may move the point of failure to a readily accessible outlet strip rather than the innards of your equipment if damage occurs. It is still best to unplug everything if the air raid sirens go off or you see an elephant wearing thick glasses running through the neighborhood (or an impending lightening storm). Generally, the backup battery or supercap will retain the clock and programming information long enough to ride out a typical storm. ----------------------------------------------------------------------------- @endnode @node 16.1 "VCR poops out after a couple of hours" What could be the cause of the video dying on a VCR after it is playing for a couple of hour? Here are some questions: o Do all modes 'go out' or just PLAY? o Does it happen suddenly or just gradually worsens until it is total snow? Or, do you get the 'blue screen' if it has this function rather than snow? o Does the tuner still work? o Conversely, does PLAY work but not the tuner? o Do other functions like FF and REW always work? o How is the time it sits turned off related to how much on time you get? o Have you verified that the TV is fine? o Is it possible that the VCR is covered up/closed in/installed with inadequate ventilation? It could be a loose connection or bad component. The usual way to narrow down the possibilities is to use what is called 'cold spray' or 'circuit chiller' on the appropriate sections of the circuit board until you locate the component that is failing with when it gets hot. I once had a VCR that needed a little fan blowing on it to keep it happy - much easier solution than actually hunting down the fault. If play or record just stopped and the tape unloaded, it could also be a mechanical problem like a marginal idler tire, idler clutch, or worn belt. ----------------------------------------------------------------------------- @endnode @node 16.2 "VCR was dropped" So your cat decided it was time to practice the long-jump and didn't quite pick a stable destination. Your VCR is on the floor, Tabby is in the basement, and what to do? Overall, VCRs are quite tough. However, falling in just the wrong way can do substantial and possibly not immediately visible damage. If you take it in for service, the estimate you get may make the national debt look like pocket change in comparison. Attempting to repair a VCR that has been dropped is a very uncertain challenge - and since time is money for a professional, spending an unknown amount of time on a single repair is very risky. There is no harm is getting an estimate (though many shops charge for just agreeing that what you are holding is a VCR!) This doesn't mean you should not tackle it yourself. There may be nothing wrong or very minor problems that can easily be remedied. First, unplug the VCR even if it looks fine. Until you do a thorough internal inspection, there is no telling what may have been knocked out of whack or broken. Electrical parts may be shorting due to a broken circuit board or one that has just popped free. Don't be tempted to power the VCR even if there are no obvious signs of damage - turning it on may blow something due to a shorting circuit board. Then, inspect the exterior for cracking, chipping, or dents. In addition to identifying cosmetic problems, this will help to locate possible areas to check for internal damage once the covers are removed. Next, remove the top and bottom covers and front panel. Check for mechanical problems like a bent or deformed cassette basket, broken or cracked plastic parts, and anything that may have shifted position or jumped from its mountings. Carefully straighten any bent metal parts. Replace parts that were knocked loose, glue and possibly reinforce cracked or broken plastic. Plastics, in particular, are troublesome because most glues - even plastic cement - do not work very well. Using a splint (medical term) or sistering (construction term) to reinforce a broken plastic part is often a good idea. Use multiple layers of Duco Cement or clear windshield sealer and screws (sheetmetal or machine screws may be best depending on the thickness and type of plastic). Wood glue and Epoxy do not work well on plastic. Some brands of superglue, PVC pipe cement, or plastic hobby cement may work depending on the type of plastic. Cycle the cassette loading and tape loading mechanism manually by turning the appropriate motor shaft, if possible. Check for free movement of the various parts of the tape transport. Inspect for any broken electronic components - these will need to be replaced. If the fluorescent panel is broken, you can run the VCR without it but of course will not be able to see any front panel displays. Check for blown fuses - the initial impact may have shorted something which then blew a fuse. There is always a slight risk that the initial impact has already fried electronic parts as a result of a momentary short or from broken circuit traces and there will still be problems even after repairing the visible damage and/or replacing the broken components. Examine the circuit boards for any visible breaks or cracks. These will be especially likely at the corners where the stress may have been greatest. If you find ANY cracks, no matter how small in the circuit board, you will need to carefully inspect to determine if any circuit traces run across these cracks. If they do, then there are certainly breaks in the circuitry which will need to be repaired. Circuit boards in VCRs are never more than two layers so repair is possible but if any substantial number of traces are broken, it will take a great deal of painstaking work to jumper across these traces with fine wire - you cannot just run over them with solder as this will not last. Use a fine tipped low wattage soldering iron under a magnifying lens and run #28-30 gauge insulated wires between convenient endpoints - these don't need to be directly on either side of the break. Double check each connection after soldering for correct wiring and that there are no shorts before proceeding to the next. If the circuit board is beyond hope or you do not feel you would be able to repair it in finite time, replacements may be available but their cost is likely to be more than the VCR is worth. Locating a junk VCR of the same model to cannibalize for parts may be a more realistic option. Once all visible damage has been repaired and broken parts have been replaced, power the VCR up and see what happens. Be prepared to pull the plug if there are serious problems (billowing smoke would qualify). Determine if it appears to initialize correctly - without shutting down. Play a garbage tape to determine if there are any problems that might damage the tape. Watch and listen carefully for any evidence of poor tracking, video noise, tape speed instability, or weak or muddy audio that might indicate that tape path alignment requires further attention. Listen as well for any unexpected mechanical sounds that were not there before. Very likely, the VCR will be fine, you can replace the covers, and now find a more secure spot for it to prevent this sort of event in the future. Use your own judgement with respect to the cat. ----------------------------------------------------------------------------- @endnode @node 16.3 "VCR or camcorder went to the beach (sand and/or surf)" Someone took your camcorder to the beach this summer and now it has sand or perhaps salt inside. Or, that cup of tea on top of the VCR wasn't as stable as you thought. Now, it behaves, well, strangely. Can this possibly be fixed? Will it be worth the effort or expense? Unless this is a really sophisticated (i.e., costly) unit, I doubt whether it will pay you to take it anywhere for repair. Even if it is successfully repaired, its reliability may be questionable. Furthermore, as with equipment that has been dropped or physically abused, few repair shops will be inclined to touch the job. They really don't like challenges of this sort. That leaves you! If anything got wet with saltwater and it has been just sitting, you can probably forget it. Without immediate attention (and I mean immediate, not later, not tomorrow, NOW!), saltwater corrosion can set in very quickly and attacks electronic components, circuit board traces, cable wiring, and mechanical parts. The only thing worse might be a peanut-butter-and-jelly sandwich 'played' in your VCR. On second thought, that probably would not be all that bad. Although it is probably too late, the first thing to do when electronic equipment gets wet is to remove the power source - pull the plug or remove the batteries. Don't be tempted to apply power until you have determined that everything is completely dried out inside and out. DO NOT use strong solvents anywhere! These may attack various plastic parts or cause internal damage to electronic components. The following was written assuming sand, salt, and liquid contamination everywhere! Modify based on your specific situation. Mechanical intensive care: 1. Disassemble as much as possible - sand and surf (or other liquids) find their way into the tiniest nooks and crannies. You need to get it all. 2. Make a drawing of the belt routing, remove the belt(s), wash and dry them, label and set them aside. 3. Use a soft brush (like a paintbrush) to dust out as much sand as possible. Hopefully, you can get it all this way. A vacuum cleaner with a wand attachment may prove handy to suck out sand. Sand will tend to collect on lubrication, especially grease, which will need to be completely cleaned out and replaced. Don't use high pressure compressed air, you will just spread it around. Any grease or oil on which sand has collected will need to be totally removed and replace with fresh lubrication. 4. If there is evidence of salt (remember, I said forget it...but), you will need to wash it off. Yes, wash it. Keep water out of the motors. Use low pressure compressed air (a blow dryer on low heat should be fine) to dry so that it does not rust. Ditto if it is still wet with contaminated liquid (we won't say where this came from), wash with fresh water to remove all traces of it as quickly as possible. Then dry completely. Depending on the situation, a final rinse with 91% or pure isopropyl alcohol may be desirable to decrease drying time. This should be safe for most mechanical assemblies. Degreaser may be used if it is safe for plastic and rubber parts. Lubricate all bearing points with a drop of light machine oil - electric motor oil, sewing machine oil, etc. (Never never never WD40). Lubricate gears, cams, and sliding parts with a light plastic safe grease such as Molylube. Parts like the idler clutch may need to be disassembled to get at the friction felt. Other mechanical parts like cam gears may need to be removed to be properly cleaned. Don't mess up the timing relationships when you do this! 5. Reinstall the belts and reassemble in reverse order. Electronic intensive care: 1. Remove the circuit boards and label the connectors if there is any possibility of getting them mixed up. If the circuit board(s) are soldered to the rest of the equipment, then you will have to improvise and work in-place. 2. Wash with water and dry thoroughly. This does work. I use it routinely for degunking remote controls and rubber membrane keypads, for example. I have heard of people cleaning contaminated computer keyboards in their dishwasher! The important objective should be to get corrosive liquids off the components and circuit traces as quickly and completely as possible. A final rinse with 91% or pure isopropyl alcohol will decrease drying time. However, there is a slight risk of damage to sensitive electronic components should some be trapped inside. Pat dry, then use warm air from a hair dryer (or heat gun on low) to completely dry everything. Moisture will be trapped in controls, coils, selector switches, relays, transformer cores, connectors, and under large components like ICs. DO NOT operate until everything inside and out is thoroughly dry. 3. Use spray contact cleaner on the switches and control cleaner on the control and adjustment pots. DON'T turn the internal adjustments without precisely marking the original position - else realignment will then be needed. However, exercise the user controls to help the cleaning process. Note: drying time may be quite long. For parts with inaccessible areas like membrane keypads, you may need to wait a week before normal operation is restored. Be patient! Once everything is completely dry as a bone and reassembled, power it up but be prepared to pull the plug or pop the batteries if there are serious problems. See if the display comes alive and the transport appears to initialize. Attempt to play a garbage tape to determine if there are any mechanical problems that might damage the tape. Look and listen for any abnormalities which may require additional attention. Then address specific problem areas. Also see the section: @{"VCR was dropped" link "16.2"} for additional info. Obviously, this description is very simplistic. The important thing is to get every last grain of sand, salt, and other contaminants off of the mechanisms and circuit boards quickly. As noted above, moisture may collect inside certain electronic parts and it is essential that these be dried completely before attempting to apply power to the unit. If you do not, at best it will not work properly and you may do additional serious damage due to short circuits. For the mechanics, the same applies though this is trickier since certain parts need to be lubricated and these may not be readily accessible or obvious. Don't be tempted to overdo the lubrication - too much is worse than too little. For camcorders, some parts of the optics or enclosed DC-DC convertors may be impossible to access and clean of scum. ----------------------------------------------------------------------------- @endnode @node 16.4 "Dead remote control units" If there is no response to any functions by the TV or VCR, verify that any mode switches are set correctly (on both the remote and the TV or VCR). Check and replace the batteries if necessary. Unplug the TV or VCR for 30 seconds (not just power off, unplug). This sometimes resets a microcontroller that may have been confused by a power surge. If it is a universal remote, it may have forgotten its programming - reinitialize with the codes for your equipment. Test the remote with an IR detector. An IR detector card can be purchased for about $6. Alternatively, build the circuit at the end of this document. If the remote is putting out an IR signal, then the remote or the TV or VCR may have forgotten its settings or the problem may be in the TV or VCR and not the hand unit. For more info, see the companion document on "Notes on the Repair of Hand Held Remote Controls". There are a large variety of universal remotes available from $10-$100. For general TV/VCR/cable use, the $10 are fine. However, they will not provide the special functions like programming of a TV or VCR. Don't even think about going to the original manufacturer - they will charge an arm and a leg (or more). ----------------------------------------------------------------------------- @endnode @node 16.5 "Recovering damaged or broken tapes" So you just pulled your favorite tape from the VCR and there are two tape ends dangling from it. Or, perhaps, your VCR has just munched on that tape and a section is now seriously crickled. Maybe you haven't been following the recommendations on preventive maintenance; maybe your VCR was just hungry. In any case, what to do? The recording is, of course, irreplaceable. Despite this, I recommend you chuck it. An imperfect splice or seriously crinkled section of tape can shatter your video heads - the most expensive single part in a VCR. If it is something you really treasure, than what I would do is the following: 1. Locate a garbage cassette and disassemble it. Throw away the tape but save everything else including the reels. 2. Construct two cassettes from the combined collection of parts you now have. Cut out any sections of tape that got mangled. Cassette 1 has the first section of tape (before the break) and uses one empty reel from the garbage cassette for the supply reel. Rewind this to the beginning. Cassette 2 has the second section of tape (after the break) and uses the other empty reel from the garbage cassette for the takeup reel. Use the little plastic plugs that came from the garbage tape reels or some adhesive tape to connect the tape to the reels. 3. If the break is at one end, you can just reconnect the bulk of the tape to the reel and dispose of the original leader. Just don't rewind or fast forward all the way to the end as the automatic end sensor will not work (for the particular end that has been repaired). 4. Copy to a good cassette. 5. Dispose of the original(s) or clearly mark 'DO NOT USE' with a detailed explanation. The idea is to never have a splice in a VHS cassette. (Even a seriously crinkled tape such as might result from a tape eating incident can damage the heads.) It is possible to splice safely but as noted, it can be quite costly if you don't get it quite right. ----------------------------------------------------------------------------- @endnode @node 16.6 "Cassette rewinder problems" Cassette rewinders typically consist of a low voltage motor powered from a built in transformer or wall adapter, a belt, a couple of reels, and some means of stopping the motor and popping the lid when the tape is fully rewound. Note that some designs are very hard on cassettes - yanking at the tape since only increased tension is used to detect when the tape is at the end. These may eventually stretch the tape or rip it from the reel. As noted, I don't really care much for the use of tape rewinders as normal use of rewind and fast forward is not a major cause of VCR problems. Sluggish or aborted REW and FF may simply indicate an impending failure of the idler tire or idler clutch which should be addressed before the VCR gets really hungry and eats your most valuable and irreplaceable tape. Problems with tape rewinders are usually related to a broken or stretched belt or other broken parts. These units are built about as cheaply as possible so failures should not be at all surprising. The drive motor can suffer from any of the afflictions of similar inexpensive permanent magnet motors found in consumer electronic equipment. See the section: @{"Motors in VCRs" link "21.1"} A broken belt is very common since increased belt (and tape) tension is used to switch the unit off (hopefully). Parts can pop off of their mountings. Flimsy plastic parts can break. Opening the case is usually the biggest challenge - screws or snaps may be used. Test the motor and its power supply, inspect for broken or dislocated parts, test the power switch, check and replace the belt if needed. That is about it. ----------------------------------------------------------------------------- @endnode @node 17.1 "Dead Clock in Hitachi manufactured VCR" The clock display is dark but other functions are normal. (From the besancon@rain.org (Fred Besancon)) Your vcr probably was made by Hitachi (Sears is one brand that may be manufactured by Hitachi). If so, probably your DC to DC converter went bad. Please note the the converter is close to the front of the vcr and not in your main power supply board. A complete kit is sold by most vendors. That is, you have to replace capacitors, transformer, etc. as well as probably an I.C. (From the Editor) Parts Express has several kits for the Hitach ($12-13) that include other parts that may have died as well. They also have the RCA part for ~$13. Another brand affected is older RCA models. Louis A. Iannotta adds; "The DC to DC converter you are replacing should be replaced together with the 3 electrolytic capacitors which could have caused it to fail along with the ICP-N10 circuit protect. RCA makes a kit with all the parts you will need to replace. The part number is 163818 and is available at an RCA distributor." ----------------------------------------------------------------------------- @endnode @node 17.2 "JVC tracking problems and dropped parts" You have a JVC VCR, 1990 or so vintage and it upped and died on you. JVC, huh? How did it die? What are the symptoms? Major tracking problems? Eats tapes? JVCs of that era tend to shed parts in the tape loading mechanism - easily fixed. Unless it is a serious electronic problem, a service manual may not help. And even then, it may not have the information you need. Check the roller guide assemblies (see the section on @{"tape path alignment" link "19"} If one of them flops around (they will be loose except in the fully loaded position but should not come off the track), then it has lost the brass guidepost underneath. Remove the bottom cover and you should see it drop out. Without the guide, the roller guide will not seat properly and tracking will be way off. Use a dab of Epoxy or superglue to replace the brass post fully against the shoulder in the cast roller guide base. If this is done carefully, tape path realignment should not be needed. Alternatively, replacement roller guide assemblies are available. Warning: do not attempt to load a tape if a roller guide assembly can be lifted off of the track - it may smash the rotating video heads - very expensive lesson. If a roller guide does not seat fully against the V-stopper (the end piece), then a linkage pin may have loosened. This is plastic pin which is the hinge for the linkage which moves the roller guide assembly. I have used a tiny screw from the top to firmly reattach this pin. Alternatively, a dab of plastic cement may work. Tape path realignment should not be needed. ----------------------------------------------------------------------------- @endnode @node 17.3 "Panasonic and clones switching power supplies" A number of Panasonic and other Matsushita brand clones use a switching power supply which has a couple of common failure modes. o Blown fuse and shorted switchmode transistor and possible other failed parts. Replacement of the obvious shorted or open parts usually cures these. Test all semiconductors and fusable resistors - do not assume that a single part is bad. If you just replace the first bad part you find, it may just be blown again by other bad parts. o Low output voltages. If the 5 V (approximately) outputs measure low, 3.5 V, for example, then there is a leaky capacitor in the power supply startup limiter. A common part number is C21 - 1 uF, 50 V. o The primary side filter and other electrolytics may lose capacity resulting in hum or ripple and regulation problems. Replacing all electrolytic capacitors in the power supply is probably the best solution. Check out the schematic for a typical Panasonic switchmode power supply available at this site. ----------------------------------------------------------------------------- @endnode @node 17.4 "Late model Sony VCR munches tape on eject" Symptoms are that upon eject, a loop of tape may be hanging out and possibly held by an arm inside the deck. The cause is gummed up lubrication on the pivot of that 'half loading arm' on the right side of the transport. It is supposed to help pull the tape out of the cassette during loading and then spring back when unloading. If the lubrication gets sticky, it does not spring back and grabs onto the tape during eject. Someone gave me a fancy Sony HiFi VCR with the request "I will pay up to $150 to fix it. Circuit City said that it could not be repaired for less than $250 because my kids had gotten into it and recommended replacement" (I wonder why). It was the stupid loading arm. Obviously, the grade-A techs at Circuit City were either under orders not to suggest repairs if they could get away with it and/or had never even taken the top off of the thing because the owner had mumbled something about his kids. I could have made a bundle off of that. I could have had a nice VCR for nothing. I just gave it back and told him about the drop of oil. ----------------------------------------------------------------------------- @endnode @node 17.5 "Symphonic/Funai brand vcr won't rewind or fast forward" (Portions of the following from: blatter@amiga.icu.net.ch ((Martin A. Blatter)) Belts and idler tires are always the first thing to check for this sort of problem but older Symphonic/Funai VCRs (Those without the 'quickstart' type mechanism) also have a small rubber bumper/stop for the brake levers, etc. on top of the deck by the tape reels. It wears out and then the lever catches don't engage properly. The old mechanism was replaced by a compact direct drive type which is mounted directly on the PCB in 1993 (at least on the European PAL models). Part #8059-02-23 is available at electronics distributors such as Fox International in Ohio or MAT Electronics in PA. Symphonic/Funai Corp, 100 North St, Teterboro, NJ 07608 phone 201 288-2606. Alternatively, just wedge a bit of plastic inside the rubber bumper to fatten it a bit or just turn it around to expose the unworn side. This works just as well as a replacement part. ----------------------------------------------------------------------------- @endnode @node 18.1 "What is a Video head?" The flying video heads in a VCR or camcorder are the actual transducers which scan the tape during REC and PLAY. The head drum or upper cylinder, as it is often called, spins at 1800 RPM (for NTSC, actually 29.97 Hz) with one complete rotation representing a video frame (525 lines in the US consisting of 2 fields which are interlaced). The result of the spinning head is to provide an effective head-tape speed of over 24 feet/second needed to achieve the required video bandwidth. The actual video heads are the nearly microscopic transducers that contact the tape and magnetically record or playback the video information. The upper cylinder is the entire rotating assembly including the video heads. The heads are aligned and locked in place on the upper cylinder at the time of manufacture and this alignment should never be touched. (Note that the terms 'video heads' and 'upper cylinder' are often used interchangeably but strictly speaking this is not correct.) The heads themselves are made from ferrite which is an extremely hard ceramic magnetic material which is also very fragile. The head chips can be seen at the very bottom of the rotating upper cylinder. The actual construction is of a 'C' shape with a very small gap between the arms of the 'C' - about 1 um or so. This is filled with with a non-magnetic material to force the magnetic field out of the head into the tape and to prevent material from collecting in the gap. A few turns of fine wire form the coil of an electromagnet for recording and as a pickup coil for playback. If you look at a head chip from below (on a cylinder that has been removed) you can see the coil and the shape of the core, though you will not be able to tell if a head is bad or worn by this inspection unless there is obvious damage). A powerful microscope is needed to even see the gap. VCRs are described as having '2 heads' or '4 heads' or whatever. This actually refers to the number of head gaps and not actual head chips though usually this is the same number. However, two head chips may be placed very close together and thus appear to be a single head when in fact there are a pair of head gaps. Therefore, without a close examination, there may only appear to be 2 heads when in fact there are 4 - in 2 pairs. You are not being short changed. Two heads are required for any play, record, or search function. Usually, these are exactly 180 degrees apart - directly opposing one another on the upper cylinder. With 4 head (or 3 head or 5 head) VCRs, various combinations of heads are used for each mode to optimize record or playback video quality by selecting a pair of heads with optimal widths and other characteristics. These may end up not being exactly 180 degrees opposed requiring video delay line to line up the two video fields in a video frame properly. This complicates head testing as it is not always obvious even which set of heads is used in any given mode. An additional pair of opposing heads is required for HiFi VHS audio and another one is present if the VCR has flying erase head. Usually, there is only a single flying erase head - it is double width and clears a pair of tracks (fields) on each pass. So, there may be up to 7 (or even more) heads competing for space on the upper cylinder! ----------------------------------------------------------------------------- @endnode @node 18.2 "Are your videos heads really bad?" No picture or snowy picture in play modes and/or failure to produce a good recording may indicate dirty or bad video heads. First, make sure that the VCR's tuner and RF modulator are working by viewing a broadcast or cable channel. Next, refer to the section on @{"Video head cleaning" link "6.3"} and follow the instructions carefully. If there is no change even after a couple of cleanings, then your video heads may have problems. Of course, if your inspection reveals any physical damage, you will need a new set of heads. Indications of a bad video head include: o Any visible damage to the ferrite chips. Heads nearly always appear in opposing pairs on the upper cylinder (head drum). Any visible discrepancy between the chips in a pair is probably damage. Sometimes 1/2 of the core breaks off leaving the windings dangling. Common causes for this damage are improper cleaning techniques or the use of damaged or spliced tapes. Use a magnifying glass and bright light to examine the heads but do not touch! By the way - improper splicing of broken video tapes is a good way to break video heads. Any kind of splicing should be avoided if at all possible. (See the section: @{"Recovering damaged or broken tapes" link "16.5"} o Excessive video snow which cannot be eliminated by the tracking controls. An image where more or less good video alternates with snow at a 30 Hz rate means that one of the 2 heads in a pair is either dirty or bad. o Excessive video snow or no picture on some playback speeds (SP, LP, EP, still) since different sets of heads (in 4 head or more) machines are often used for different speeds. If this is due to wear, then it would probably gradually deteriorate and not happen suddenly. o Inability of certain internal adjustments such as backtension to eliminate erratic tracking problems may indicate a worn video head. Horizontal bands of video noise may come and go at various places in the picture depending on what speed is being used or the playback location on the tape (beginning, middle, end). These may come and go in a periodic cycle. o Need to frequently clean the video heads even if you are only using new good quality (name brand) tapes. Video heads are normally self cleaning but very worn heads can tend to collect tape oxide resulting in a noisy, snowy, or totally missing picture. o You have just been playing a rental, damaged, or spiced tape and you notice any of the above symptoms. If your VCR has HiFi audio, similar symptoms may apply to the HiFi audio heads on the rotating drum. Noisy or loss of HiFi audio or erratic switching between linear and HiFi audio may be due to bad HiFi audio heads (but could also be a tracking problem since HiFi audio tracking can be even more critical than video tracking). However, many other problems can result in similar symptoms - video head diagnosis is one of the most difficult to make (except for physical damage). Some pros claim to be able to determine if a video head is worn by feeling it with a finger. I can guarantee that you will not be able to do this, so the set of guidelines given above is the best to go on. ----------------------------------------------------------------------------- @endnode @node 18.3 "Need for video head cleaning" When should you clean a video head? Only when symptoms point to a problem with the head. See section on @{"video head problems" link "18"}. Periodic cleaning is not necessary and may cause excessive wear if done with a head cleaning tape, especially the dry kind which may be excessively abrasive. Frequent cleaning by hand, while not damaging, still represents a slight risk since you never can tell when you might do something you will regret! VCRs should be cleaned periodically, but video heads usually do not need periodic cleaning as the spinning heads performs a self cleaning function. If it ain't broke, don't fix it. I do not see any advantage in buying a VCR which claims to have automatic video head cleaning. As noted, video heads are basically self cleaning in any case. The automatic head cleaner is a foam roller that contacts the rotating heads for a couple of seconds when the tape is loaded. In my opinion, this is worse than useless as any crud collected by this foam may just be redeposited on the heads during the next cleaning cycle. ----------------------------------------------------------------------------- @endnode @node 18.4 "Video head cleaning technique" Caution: Read the following in its entirely to avoid an expensive lesson. As noted, improper cleaning can ruin your expensive video heads. The head chips are very fragile and just rubbing them in the wrong direction (NEVER use an up-and-down motion) can break them clean off. Manual cleaning using the proper head cleaning sticks is best but requires that you gain access to the interior of your VCR - i.e., take off the cover. If you do not want to do this, you can try a wet type head cleaning tape. I do not recommend the dry type as they are much more abrasive and may cause premature wear of your video heads especially if used regularly. When using the wet type cleaning tapes, follow the directions and - very important - wait sufficient time for everything to dry out Regular video head cleaning should not be needed! Therefore, the regular use of a cleaning tape is not recommended. As noted, some cleaning tapes will cause excessive wear to the video heads and no cleaning type can adequately deal with other parts of the tape path anyhow. If you find yourself needing to clean your video heads frequently, the video heads may be worn, the backtension may be set too high, or you may be playing old or dirty (literally) rental tapes. To clean by hand, you will need what are called 'head cleaning sticks'. These are covered by chamois and are safest. DO NOT USE QTIPS (COTTON SWABS). These can catch on the ferrite cores and damage them or leave fibers stuck in the heads. Qtips can be used for cleaning the other parts like the rollers and audio/control head as described above but not video heads. To use the cleaning stick, moisten it with head cleaner or alcohol. Pure isopropyl is best, however, the 91% medicinal stuff is ok as long as you dry everything pretty quickly. Don't flood it as it will take a long time to dry and you run the risk of any water in the alcohol sitting on surfaces and resulting in rust (very unlikely, but don't take the chance). Gently hold the flat portion of the chamois against the upper cylinder where it is joined to the lower (non-rotating) cylinder. Rotate the upper cylinder be hand so that the heads brush up against the moist chamois. DO NOT MOVE THE HEAD CLEANING STICK UP-AND-DOWN - you will break the fragile ferrite of the heads - $$$$. Side-to-side is ok as long as you are gentle. I know people who use a piece of moistened typing paper or a business card, or even their Mark-1 thumb for video head cleaning but I would not recommend these for a general service procedure! (I suppose the only real requirement to prevent damage is that the material have a fine enough structure and not have fibers that can get stuck in the heads. So, the short list of acceptable materials is quite long - some more effective than others. My concern for a general recommendation is that people's interpretation of these requirements can vary quite a lot. If a novice comes to me and asks what to use, I will say 'cleaning sticks'. Once they understand the characteristics of the heads and their mounting, they are free to use whatever works.) Depending on how dirty your heads are, a couple of passes may be enough. Let everything dry out for at least 1/2 hour. This process can be repeated. However, one pass will usually do it. In addition, inspect and clean the drum itself staying safely away from the video head chips. The five fine grooves in the drum help control the air bearing that the tape rides on and helps to stabilize tape motion. These should be clear of dirt and tape oxide (DO NOT use anything sharp - the moistened head cleaning sticks will work). ----------------------------------------------------------------------------- @endnode @node 18.5 "Advanced video head testing techniques" Assuming cleaning does not help and you have the time and inclination, some additional test can be performed to confirm or rule out a bad set of video heads (upper cylinder). To check the signal from the video heads you need a circuit diagram so that you can locate the relevant test points and expected voltage levels in the head preamp. This will be housed in a metal enclosure, usually right next to the head assembly (at the rear). This should be done with an alignment tape, but any known good recording should provide a reasonable approximation. Other basic checks such as visual check with a magnifying glass, continuity tests on the heads as well as power supply voltages in the preamp can also help. If your VCR has 4 video heads (not including HiFi audio heads) and only certain modes or speeds do not work, then the following procedure may permit you to isolate the problem to a head or its preamp. Basically, the idea is to interchange the wiring of the two pairs of heads. While the heads will no longer be optimized properly for each mode, there is a good chance that they will work well enough to determine gross changes. For example, if SP play originally had alternating fields of good and bad video and works moderately well after this rewiring (but maybe with tracking noise), then you know that the bad head is no longer being used for SP play. Since the same head preamps are being used, a bad head must be at fault. Video drums where the heads are wired with flying leads are somewhat easier to cross-wire than those with a PC board. This is not fun and may not work in all cases, but if you are hesitant to risk the cost of a new head, it may be worth a try. ----------------------------------------------------------------------------- @endnode @node 18.6 "Where to obtain replacement video heads" Once you have concluded that a replacement head is required, you need to decide whether you will undertake this yourself or take the VCR to a shop. Video head replacement is relatively straightforward and low risk as long as you are comfortable working on mechanical devices and take your time. A little unsoldering and soldering is usually required. Electronics suppliers such as MCM Electronics, Premium Parts, and Dalbani stock a wide range of video heads for VCRs that are more than a couple of years old. (They may not have heads for the latest models.) In some cases, they will offer two kinds of heads for the same model - a generic version and a 'name brand'. Unless you are extremely critical, there is probably no need to spend the extra on the 'name brand' head. There is also no need to pay the premium charged by the original manufacturer of your VCR - it is often priced 2:1 or more over what a generic head will cost with no substantial difference in performance, if any. You may even end up with exactly the same head manufactured on the same assembly line! Note that currently, the price of many upper cylinders (video heads) for 2 head VCRs is well under $25 so ordering a replacement may be a better investment of time and effort than a long diagnostic procedure especially if the old head has high mileage and video quality has been steadily decreasing. ----------------------------------------------------------------------------- @endnode @node 18.7 "Video head replacement technique" 1. Do not touch the actual video head chips themselves. Handle the head as little possible. You can touch the upper part of the head cylinder if necessary. One thumb through the center hole with fingers resting on the upper edges works pretty well. 2. Before you unmount the old one, mark or make a note as to its position - sometimes it is possible to mount the new head 180 degrees off from way it is supposed to be oriented causing tracking problems at the least as the opposing heads are not identical. (The azimith angles are +/- 6 degrees for VHS). 3. Unsolder the connections between the head and the upper cylinder. There will be 2n solder connections for an n head VCR. (Sometimes there is some kind of connector rather than solder connections, but this is rare.) Examining the new head should reveal exactly where to unsolder. For pins through the printed wiring board type, you should use some kind of desoldering tool - solder pump, SolderWick, or a vacuum rework station. 4. Unscrew the 2 or 4 philips head screws holding the old head in place. It should be obvious from the new head which screws need to be removed. You may need to remove the static brush if your VCR has one or some other usually obvious stuff to get at it. DO NOT touch any other screws on the head drum as these are critical adjustments one should not mess with. 5. Lift the old head straight up and off. You should not need to use any drastic measures though a little jiggling may help. I have never actually needed a head puller. 6. Replace in reverse order, solder the connections, replace any other hardware that was removed. Refer to your notes on the position of the old head and/or the color codes (wire colors, dabs of paint, etc.) as to orientation on the drum. 7. Carefully clean any fingerprints from parts of the head drum you touched. Again, do not touch the video head chips themselves. You may use 91% medicinal alcohol, though pure isopropyl is preferred. Avoid rubbing alcohol especially if it contains any additives. Let the machine dry completely. 8. Unless you tweaked any mechanical adjustments, the VCR should work fine assuming the video head was the problem. If the tracking is way off, refer to your diagram and double check that you didn't replace the head rotated 180 degrees from the proper position by accident. ----------------------------------------------------------------------------- @endnode @node 18.8 "Can I substitute a video head from another VCR?" The quick (and long) answer is: NO. The heads themselves are in no way standardized. You can substitute a video head drum (upper cylinder) if it is identical - VCRs sold under different labels are often manufactured by the same few companies. Check a cross reference if you have a dead VCR with a good set of heads but not the same model as the one you are trying to repair. As far as the heads themselves, don't even think about attempting to interchange the actual head chips - even if your replacement were physically and electrically compatible, you would never be able to get the alignment within tolerance since you do not have the factory jigs. Not to mention that the head chips themselves are really really tiny and really really fragile and their specifications all vary - head width, azimith angle, etc. Forget it. ----------------------------------------------------------------------------- @endnode @node 19.1 "General tape path alignment problems" There are separate descriptions of the procedures for adjusting the various components of the tape path - in particular, A/C head azimith, tilt, and height; and roller guide height. Before you attempt these, you need to determine whether either of these are likely to be your problems. The following are some symptoms you may experience indicating the need for A/C head adjustments: o Weak, muddy, or wavering sound. (Azimith, height, or tilt adjustment). o Tracking incompatibility between this VCR and tapes recorded on other VCRs - you always need to adjust tracking or keep the tracking control way off center when playing tapes from other VCRs. However, if it is only one other VCR, that VCR may be misadjusted. (Mechanical tracking adjustment). o Erratic loss of synchronization or frame lock, or speed changes. (Height or tilt adjustment). Before you try to adjust the A/C head, make sure that there is not some obvious mechanical problem that has shifted its position. There may be a bit of something stuck in the mechanism. If this appeared after you did some work on the VCR, you may have accidentally caught a cable or something else preventing the A/C head assembly from returning to its proper position. This is particularly likely if the problem happened suddenly. Once you change its settings, any tapes recorded on your VCR prior to these adjustments may not play back properly. For example, if you touch the A/C azimith screw to correct a muddy weak sound problem when playing tapes from other VCRs, any tapes previously recorded on your VCR will now sound muddy and weak. You need to decide which is more important - your recorded tape library or compatibility with other VCRs. The following are some of the symptoms you may experience indicating the need for roller guide height adjustments: o Video noise at top or bottom of picture that cannot be removed with the user tracking control. o Video noise in various areas of picture that comes and goes in a few second cycle. o A jumpy picture - as though the vertical hold control (which most TVs no longer have) is misadjusted. Before you try to adjust the roller guide height, make sure that there is not some obvious mechanical problem which is preventing the roller guides from seating properly. This is particularly likely if the problems happened suddenly. See the section below on: @{"Likely causes for sudden change in tracking behavior" link "19.4"} ----------------------------------------------------------------------------- @endnode @node 19.2 "Adjustment of A/C head - problems with tracking or sound (linear audio)" If the problems happened suddenly, it is probably not a misadjusted audio/control head but some other mechanical fault - eliminate this possibility before considering A/C head adjustments. The following will attempt to get your mechanical settings back to something approaching normal even if the audio/control head was tweaked: I assume that you have cleaned it and replaced any dead rubber parts. I also assume that someone (we won't name anyone) has tweaked just about every mechanical adjustment. I would adjust the audio/control (A/C) head as best you can (don't touch this unless you know it was messed up by someone): o Play a tape that you know was recorded on a good machine. It may be easier to start with a tape recorded in SP mode since this is less critical. Once the basic alignment is complete, go back and fine tune with a tape recorded in EP. o Adjust the A/C tilt as vertical as you can by eye. If necessary, fine tune it for most stable tape movement - the tape should be at the same angle moving over takeup roller guide, A/C head, and adjacent fixed I guide. o Adjust the A/C height for loudest sound. At each end of the range of this adjustment, you will lose tracking/sync and tape speed may fluctuate (in addition to the sound becoming weak). o Adjust the A/C azimith for best treble (high frequency) sound. This is a precise adjustment - a 1/16 of a turn is significant. There will be a very small range over which the sounds will be clear and natural. A tape with music is best for making this adjustment. o With electronic tracking control centered, adjust A/C mechanical tracking (usually, a conical nut that moves the entire A/C assembly) until you get the least snow (if you have a picture at this point). Satisfactory tracking may be obtained at several positions of this control. However, only one will produce current video-audio sync. For the others, the words and the picture will be off by some multiple of 1/30th of second. o You may need to go back and touch up some of these again. There can still be other problems in the tape path including the height and angle of the roller guides and the height of the impedance roller assembly (on the left before or after the full erase head.) ----------------------------------------------------------------------------- @endnode @node 19.3 "Roller guide height adjustment" You can do this by eye. Sophisticated test equipment and expensive test tapes are not needed. One trick is of course not to mess with both guide posts at the same time - but even if you do it isn't the end of the world. This doesn't even require a scope - the video picture is an excellent alignment tool! It does take patience and a steady hand. Also, have you touched any other mechanical adjustments - other guideposts, etc? Hope not. Also, I assume that any repairs to the guideposts have left them perfectly vertical - if they are tilted, then other tape path instabilities can result. The following checks and adjustments are made in PLAY mode. There is a ridge on the lower (stationary cylinder) on which the tape should ride - not above and not below. Play a tape that is in good condition and look closely at its bottom edge to see if it is sitting precisely on this ridge. If it is not, first verify that both roller guides are snug against the 'V-stoppers' - the brackets at the end of the tracks where the roller guides stop in PLAY and REC. If they are not, then you need to determine what is binding or what has fallen off of the tape loading mechanism. See the section on: @{"General tape path alignment problems" link "19.1"} Assuming that the roller guides are correctly positioned on the tracks, the first step is to visually adjust the roller guides so that the tape just rides on that ridge on the lower cylinder. That ridge is a very critical part of the guide mechanism. There will be a set screw to lock each of the roller guideposts from turning. The appropriate one(s) will need to be loosened slightly - just enough to that the post is snug but can be turned by hand. The set screws may require a miniature metric hex wrench. Some just have a square head screw which can be loosened with a pair of needlenose pliers. Adjust each guidepost so that the tape just rides on top of the ridge. Now, for the fine adjustments. Which part of the picture is bad? o Left guide -> mostly problems with top of picture. o Right guide -> mostly problems with bottom of picture. Misadjustment can also cause a periodic loss of sync on a several second cycle. Make careful SMALL adjustments of each one - then wait for a few seconds for any results to become apparent. Since the tape moves so slowly, it takes several seconds for the tape motion to stabilize to the new guide position. The left guide will affect the top part of the picture (mostly) and the right guide will affect the bottom. Once you are happy with SP, get a tape recorded on a known good deck in EP (SLP) mode since the tracks are narrower and fine tune it. Tape path alignment comments: 1. An EP recording requires the best tracking, and will thus make the best test source. (But it must have been recorded on a unit that was aligned properly). 2. Using forward and reverse search modes helps to narrow the adjustment. The guide height on the "feed" side for whichever direction you're going will have more affect. In other words, tweak one while searching forward, and the other while searching in reverse. 3. You could have the tape centered at the middle of the contact path, but too low at one end and too high at the other. 4. You could have the entire contact path too high or too low, and be in- advertently "correcting" by misadjusting the tracking control. You could be off by an entire track getting a good but very unstable picture since the ridge is not providing any guidance. Roller guide tilt: The roller guides (but not the fixed guide posts next to them) should be perfectly vertical. Sometimes there is an adjustment for this but usually not. Roller guide assemblies that have tilt due to wear will need to be replaced. ----------------------------------------------------------------------------- @endnode @node 19.4 "Likely causes for sudden change in tracking behavior" If it is impossible to find a position of the user tracking control that results in a stable picture, this section is for you. Some amount of the picture may be noisy - top or bottom - or the tracking may be fluctuating with a few second cycle. Mostly, these symptoms are related to problems with the roller guide assemblies. (though electronic causes are also possible). The roller guides are on the assemblies that move on curved tracks to wrap the tape around the video head drum in play and record modes (and on newer instant start VCRs, other times as well). Each roller guide assembly includes a white cylindrical roller which should turn freely on a metal guidepost, and a fixed guidepost at approximately a 20 degree angle. 1. Roller guides not fully engaged against 'V-stoppers' (the metal brackets at the end of the track on which the roller guide assemblies move when entering PLAY or RECORD modes. Common causes: o Obstruction or ridge on track preventing guides from completing their movement. Visually inspect and observe behavior while entering and leaving PLAY mode. Sometimes with use, an edge develops and the guide gets hung up. A fine file can sometimes remove this. o Parts have fallen off (don't laugh - JVCs tend to do this). Various parts of the mechanical linkage that move the roller guides may loosen with use and either fall off entirely or change position enough to prevent full engagement. Compare left and right roller guide assemblies, they are usually nearly identical in their operation and you should be able to identify parts missing or out of position. These are usually on the underside of the deck and will necessitate removing the bottom cover (unplug the unit!). To gain access to critical parts of the linkage which may be obscured by circuit boards or other components, you may need to power the VCR, turn it on, press PLAY, and then pull the plug just as the roller guides are in the middle of the track and accessible. For the JVC problems, the parts are usually either a brass post or a plastic link. The brass post can be glued back in place using a drop of Epoxy. Make sure its shoulder is fully flush with the body of the roller guide casting. For the plastic link, I have used a very small screw to secure it in place from above. Some plastic cement may work as well. o Tracks on which roller guide assemblies slide are dirty and/or need lubrication. Clean and grease. o Obstructions such as toys or Cheerios blocking tracks. Check the roller guides while the machine is playing a tape. They should be firming pressed against the V-stoppers. Any looseness indicates a problem preventing full engagement. If pushing the offending guide into position fixes the tracking problem, this confirms the diagnosis. Note that in modes where the roller guides are retracted, the roller guide assemblies are relatively loose and free to move. However, the amount of movement possible should be similar for the left and right roller guides and you should not be able to lift either entirely off of the track - the ability to do so means missing parts underneath the deck. If the missing parts can be located, they can usually be glued back into position. Warning: if you find a roller guide assembly that can be lifted off the track DO NOT attempt to load a tape - the floppy roller guide assembly can smash into the spinning video heads ruining them - and your entire day. 1. One of the fixed guide posts next to roller guides (the ones that are tilted about 20 degrees) have worked loose and fallen off. There should be a tilted guide post next to each roller guide. If one is missing, it has probably fallen into the machine. Immediately unplug (to avoid the possibility of it jamming something and/or shorting components in the electronics). Locate the escaped post - turn the unit upside down, sideways, shake it, whatever until the loose post falls to the table or floor. Glue it back into position with a drop of Epoxy or other household cement. 2. The backtension band has come loose or broken. The backtension band provides the force needed to keep the tape pressed against the video and audio head. A backtension lever on the left side just as the tape leaves the cassette is connected to a felt lined metal band that presses against the edge of supply reel. The position of the level determines the tension and is set up with mechanical feedback so that the tape tends to move it against spring force just enough to provide the correct amount. Test by moving the backtension lever a bit in each direction - you should be able to observe the tension change. Backtension bands are easily replaced. See section on @{"backtension adjustment" link "19.5"} 3. Mechanical damage due to trauma such as VCR falling off of TV. Cure, if possible, will depend in extent and type of damage. ----------------------------------------------------------------------------- @endnode @node 19.5 "Backtension adjustment" Most VCRs use a backtension band - a thin metal band with a felt liner - to apply a carefully controlled torque to the supply reel during forward tape motion in play, record, and CUE. A backtension lever or arm contacts the tape as it leaves the supply side of the cassette and provides feedback to control the tension on the backtension band and thus how much it resists the rotation of the supply reel. If the backtension is too low, poor tape-head drum contact results and you get a noisy intermittent picture. If the backtension is too high, there will be excessive head wear and in extreme cases, the drum will slow or stop entirely. Backtension is normally set using a special backtension gauge which you most likely do not have. If you own a TV with a vertical hold control, you can adjust backtension by setting the vertical hold so that you can view the head switching point - just above the vertical blanking bar. Above this point, you see the video from one head and below you see it from the other. When properly adjusted, these two segments should more-or-less line up. There are two adjustments for backtension: a spring position and the effective length of the band. To set the length, there is a setscrew which allows the end of the band to be moved back and forth. It is unlikely that you would need to set this unless you have just replaced a band or unmucked someone elses repair attempt. I usually consider the length to be correct when the angle that the tape makes going around the lever post is about 90-120 degrees. In other words, the tape should not be so tight as to not be deflected by the arm but should not be so loose as to be near or at the end of its possible travel. Then, set the spring force to align the picture above and below the head switching point. If you do not have access to vertical hold, you may be able to set backtension in the middle of the range where flag waving (see the section on: @{"Flag waving" link "12.7"} is absent or minimized. ----------------------------------------------------------------------------- @endnode @node 20.1 "Tape start/end sensors" VHS cassettes use a clear leader and trailer for the purposes of detecting beginning or end of tape. A light source that pokes up in the center of the cassette illuminates photodetectors on either side of the cassette through passages in the plastic passing through the tape as it leaves and enters the cassette. The light source can fail - this is common on older VCRs where this was an incandescent lamp but rare on modern VCRs which use a special IR LED. The failure of this light source can produce a number of symptoms: o The VCR may simply shut down and refuse to do anything. VCRs with incandescent lamps often were able to figure out that the light bulb was burnt out since it was drawing no current and then shut down or flash an error code. o The VCR may go through the motions of playing a prerecorded tape thinking that a tape is present because the sensors return signals indistinguishable from what it would see if a tape were present. Eventually, it may give up and probably shut off power. o The VCR may do strange things when you attempt to load a cassette since the microcontroller is receiving conflicting signals - the cassette is out but the sensors think otherwise. If your VCR uses an incandescent lamp and it is not lit when power is on, then the bulb is most likely burnt out. If either sensor fails open, then similar symptoms may result. If the sensor on the supply side fails shorted, then it will appear as though the tape is at the end. The VCR may refuse to play or FF or will attempt to rewind as soon as a cassette is inserted. If the sensor on the takeup side fails shorted, then it will appear as though the tape is at the beginning. The VCR may refuse to REW. In both cases, sometimes you can trick the VCR into cooperating and confirming that there is a sensor problem by pulling the connector for the appropriate sensor once the cassette is loaded. If you can get at the connectors, you can test the sensors by monitoring the voltage on the outputs. One test you might try if the VCR attempts to play an imaginary prerecorded tape as soon as power is turned on is to locate the microswitch for record lockout protection - it will be located near the front (where the record protect tab would be once the cassette is loaded). Press this in while you turn power on. If the VCR now just initializes and displays cassette-in without trying to play, then it really thinks there is a cassette in place most likely due to a faulty sensor. In some cases, there could be other problems like a faulty mode switch or microcontroller producing symptoms that might be mistaken for faulty start/end sensors. ----------------------------------------------------------------------------- @endnode @node 20.2 "Start/end sensor testing" The start and end sensors are usually a combination of a light source (IR LED) and IR photodiode. With a little effort, these can be tested for functionality. For an incandescent lamp (older VCRs), if it is not lit with VCR power on, it is most likely burnt out. Test with an ohmmeter. For an IR emitter, an IR detector like the circuit provided elsewhere in this document or an IR detector card can be used to determine if the LED is operating. You can also try powering the LED with a low voltage supply and 500 ohm or so resistor using the IR detector to see if it works. Disconnect it from the circuitry first! Try both polarities to be sure you got it right. The sensors themselves can be tested by disconnecting them from the circuitry and shining an IR source on them (a remote control or incandescent bulb) while monitoring the resistance with a VOM or DMM. Use the polarity which give the higher reading (reverse bias). This resistance should drop dramatically if they are functional. ----------------------------------------------------------------------------- @endnode @node 20.3 "Tape counters" There are two kinds of tape position counters: reference and real-time. What I call a reference counter is what all VCRs used up until a few years ago. A sensor counts revolutions of the takeup reel (usually) either directly or via a belt drive. A mechanical or electronic counter displays an arbitrary number which provides some idea of location. Since the rotation rate of the reel is not constant with respect to the actual time of the tape, it is not possible to use this for anything other than a reference. In addition, the tape may slip a bit and be wound tighter or looser depending on whether it was wound in play, FF, or REW. Thus, even the reference is not accurately repeatable. Failures can be caused by a broken or weak belt for the mechanically operated counter or defective circuitry for the electronic display. A failed sensor would most likely also cause the VCR to shut down and unload the tape as this is what is used to confirm that the takeup reel is rotating and that tape is not spilling into the bowels of the VCR. Real-time counters - which really are a vast improvement - operate off of the control track pulses from the control head. Tape location is measured in hours, minutes, and seconds though it is still relative and must be reset at the beginning of the tape if an absolute location is to be determined. One characteristic of the real-time counter is that it will not keep track of location on a tape that has not been recorded (no control track). Therefore, if you want to leave a specific length section of tape blank, you will still need to lay down the control track by recording a blank channel or just ignoring what you have recorded later when you go to fill it in. Failure of the real-time counter on a VCR that otherwise works normally is quite unlikely and is probably an electronic problem since the control head must be functional for all record/play modes to work properly. ----------------------------------------------------------------------------- @endnode @node 20.4 "Reel rotation sensors" Reel rotation is detected most often using optical sensors under the reels though some older VCRs may use mechanical or optical interrupters driven off of belts from the reel spindles. There will always be a takeup reel sensor. It has two functions: to (1) confirm that the reel is rotating and that tape is not spilling into the bowels of the machine and (2) to operate the (non-real time) tape counter. Failure of this sensor will cause the machine to shutdown almost immediately and will result in a stuck tape counter. Many VCRs will have a similar sensor on the supply reel. The output from this sensor will be used to confirm proper rotation of both reels both during modes involving tape motion as well as during the tape load and unload operations. Some fancier VCRs will display an estimate of tape remaining using the difference in rotation rates of the supply and takeup reels based on assumptions about tape thickness, hub size, and total length (which you may have to tell it). Sometimes, reel rotation sensor problems are simply due to accumulated dirt on the reflective surfaces - clean them. In other cases, replacement sensors will be needed. While you are at it, replace both sides where appropriate - most of the cost to you is in your time, the cost of the sensors themselves is modest. ----------------------------------------------------------------------------- @endnode @node 20.5 "Reel rotation sensor testing" First, locate the LED and photodiode. You can tell the difference by testing with a DMM on its diode test scale - the LED will have the higher forward voltage drop. Momentarily touch and remove a resistor (1K ohms or so should work) across the sensor leads while the VCR is in PLAY mode before it quits. This should make the counter change if the the LED is bad or the photodiode is open. Alternately, a remote control may be able to activate it providing pulses that will look to the counter exactly like reel rotation. If this has no effect, unsolder the sensor (or unplug the sensor assembly from the main board if there is a connector) and try the resistor across the terminals where it was connected. If you now get a response, the sensor was shorted (or the connection was bad). If you do not get the counter to change in either case, there is a problem with the electronics on the main board or a bad connection leading to the main board. You will need to obtain the service manual or trace the circuit leading to where the sensor signal is detected. It is possible that the counter will only change when the microcomputer expects the reel to be moving, so a test while in STOP mode may not be valid. An alternative test is to use an ohmmeter across the photodiode on a high ohms scale. Use the polarity which gives the higher resistance and shine a light on the sensor. The resistance should drop dramatically with a bright incandescent light (these put out a good amount of IR). If it is infinite in both directions, the photodiode is open. If it is low in both directions, it is shorted. You may be able to make a measurement while the sensor is still in circuit, though other components may mask the resistance change. As noted, the IR sensor/LED combination is often a pluggable assembly. Using my VOM on a photosensor, I read infinite ohms with no light and 200 ohms with a bright light. However, your mileage may vary. ----------------------------------------------------------------------------- @endnode @node 21.1 "Types of motors in VCRs" There may be anywhere from 2 to 6 or more motors in your VCR. Some designs use a single motor to power all functions except the video head drum. Others have separate motors for each function. Most typical are 3 or 4 motors. Motors perform the following functions: 1. Cassette loading (front loaders only). 2. Tape loading (position tape around video head drum, etc.). 3. Video head drum rotation (servo controlled). 4. Capstan rotation (servo controlled). 5. Takeup reel rotation (PLAY, REC, FF, CUE). 6. Supply reel rotation (REW, REV). The video head drum (3) always has its own motor. It is internal to the lower cylinder or above the upper cylinder (except in the very oldest VCRs) and directly drives the spinning upper cylinder. Most consumer VCRs use a single motor for the capstan and the takeup and supply reels. Some also use this same motor for cassette and/or tape loading. Several possible types of small motors are typically used in VCRs: 1. Small brush-type permanent magnet (PM) DC motors similar to those found in small battery operated appliances, CD and tape players, and toys may be used for cassette loading and/or tape loading. 2. A similar but larger PM motor may provide power for the capstan and reel rotation and possibly multiple other functions (older VCRs). 3. A single low profile or 'pancake' brushless DC motor may provide power for a direct drive capstan, reel rotation, and possibly multiple other functions. 4. Brushless DC or 3 phase direct drive motors are usually used for the video head drum. Some of the very earliest VCRs used a belt drive for the video head drum. ----------------------------------------------------------------------------- @endnode @node 21.2 "Repairing small motors" Aside from obvious mechanical problems and lubrication if needed, you usually cannot do much to repair defective motors. If you enjoy a challenge, it is sometimes possible to disassemble, clean, and lubricate a motor to restore it to good health. However, without the circuit diagram, even knowing what the proper voltages and signals should be on (2) or (3) type motors would prove challenging. The following are some of the possible problems that can occur with the basic permanent magnet motors: o Open or shorted windings. o Partial short caused by dirt/muck or carbon buildup on commutator. o Dry/worn bearings. An open or shorted winding may result in a 'bad spot' - a position at which the motor may get stuck. Rotate the motor by hand a quarter turn and try it again. If it runs now either for a fraction of a turn or behaves normally, then replacement will probably be needed since it will get stuck at the same point at some point in the future. Check it with an ohmmeter. There should be a periodic variation in resistance as the rotor is turned having several cycles per revolution determined by the number of commutator segments used. Any extremely low reading may indicate a shorted winding. An unusually high reading may indicate an open winding or dirty commutator. Cleaning may help a motor with an open or short or dead spot but most likely it will need to be replaced. Note that unlike a CD player which uses some motors constantly, the small PM motors in VCRs are only used for loading operations and are generally quite reliable unlee damaged by other problems. ----------------------------------------------------------------------------- @endnode @node 21.3 "Capstan problems" Capstans are expensive especially if they are integral with the capstan motor, but unless it is bent (very unlikely), or the bearings are totally shot, or it is direct drive and the motor is bad, the capstan should not be a problem as long as you CAREFULLY clean off all of the black tape oxide buildup with alcohol and a lint free cloth or Q-tips. Don't get impatient and use anything sharp! The black stuff will come off. A fingernail may help. A dry bearing may need a drop or two of light oil (electric motor or sewing machine oil). Sometimes, there is a bearing cover washer that works its way up and interferes with the tape movement. Push it back down. Some Sony VCRs have had problems with defective capstan motors resulting in intermittent pausing or stopping of video playback when hot. The entire motor or just the bearing assembly needs to be replaced in this case. ----------------------------------------------------------------------------- @endnode @node 22.1 "Why is a tracking control needed" In order for the video to be read off of the tape properly, the spinning video heads must be centered on the very narrow diagonal tracks. The width of these tracks is as small as .019 mm. The actual reference point is not on the video heads but the A/C head - several inches away. The control pulses put down during record are used to phase lock the capstan to the spinning video heads. The distance between the control head and the video heads determines whether the required centering will be achieved. In the ideal world, the distance would be identical for all VHS VCRs - that is the goal. It is part of the VHS specification. However, whether from wear and tear, or even if the technician doing the setup in the VCR factory had an off day, this distance may not be quite identical on the VCR that the tape was recorded on and the machine being used for playback. Therefore, a way is needed to adjust the effective distance. A mechanical control would be possible but not very elegant. Therefore, an electronic tracking control is provided. This basically allows adjustment of the time delay or phase of the control pulses from the control head during playback. Record tracking is fixed. Actually, there may be as many as three tracking controls: (1) the user tracking knob or buttons, (2) an internal master tracking adjustment, and in fancier models, (3) an autotracking servo system. (Note: tracking is always automatically reset to the default when a cassette is inserted.) ----------------------------------------------------------------------------- @endnode @node 22.2 "Old clunkers and the march of technology" It always amuses me to listen to comments about how anything older than 6 months (or 30 minutes) should be tossed in favor of some newer, more cheaply made piece of crap. Yes, convenience features and HiFi audio have made newer VCRs a lot nicer in many ways. But for time shifting and the kids, that old clunker will do just fine, thank you. Some of the older VCRs will just keep going and going and going and going with a cleaning and a few rubber parts from time-to-time. On the other hand, I had to repair my high-end (for 1990) moderately used Mitsubishi VCR because a 10 cent plastic part broke (their cost, my cost - $10) - clearly an exercise in design-to-fail engineering. For about .5 cents more, it could have been built never to fail. The replacement part was identical to the original, so I give it about 4 years. ----------------------------------------------------------------------------- @endnode @node 22.3 "Can I add an S-Video input to my VCR?" Possibly, but why bother? You will most likely be limited by the VCR's circuitry anyhow. All S-Video means is (1) a special connector and (2) separate luminance (Y) and chrominance (C) rather than composite video. In a VCR, you will need to bypass the input circuitry and get to the place where Y and C are separate. This may or may not be possible depending on its design. It is probably not worth it as you will likely not gain much in picture quality but if you really are determined, a schematic will be essential. If all you want to do is allow for an S-video input, there are single chips which will combine the Y and C into a normal composite video signal. ----------------------------------------------------------------------------- @endnode @node 22.4 "Can a VHS VCR record single video frames at a time?" It would be nice if it were possible to output still frames from a PC, for example, to record computer animation on video tape. This would permit images to be generated slowly and then played back in real-time. However, there are a couple of problems with attempting to cleaning record single frames on a consumer grade VCR: o Without moving the tape, only a single field (of the two interlaced fields in a video frame) can be recorded since the tracks for the A and B heads will be superimposed. I doubt that any VCR not specifically designed for single frame recording has any support for moving the tape in this manner. o The control and synchronization circuitry to cleanly switch the record for a single frame may not exist. This will depend on the model - the more sophisticated the editing functions that are supported, the more likely that this precision will be supported. o The VCR must have a flying erase head or you must use new or pre-erased tapes to avoid the rainbow interference on the first few hundred frames of any recording made over old video. Other than that, there is no reason that the video writing circuitry cannot be turned on during pause - some VCRs will do this if you go into record mode while in pause. Obviously, anything you can do from the front panel or remote you can do under computer control. There could be hidden functions accessible via a special connector or key sequence but you would need documentation for your unit which may not be readily available, if at all. ----------------------------------------------------------------------------- @endnode @node 22.5 "Why is a special VCR needed for multiple video standards?" A VCR is not simply 'analog playback' in the same way that an audio recorder doesn't care whether you record classical or rock. The VCR must synchronize to the video timing and demodulate the luminance and chrominance information in order to lay down the tracks on the videotape. There are enough differences among world video formats that while technically possible (and such multiformat VCRs exist) it is not automatic - or free. The video timing and modulation techniques for video formats like NTSC, PAL, SECAM, etc. are sufficiently different that additional circuitry is necessary to handle multiple formats. In the U.S. at least, there is not enough demand to justify the added expense. The technology of video recording makes interesting reading and the sophistication of the circuitry and mechanism of a $200 VCR is quite amazing. TVs are more likely to accommodate difference standards than VCRs. Even a regular TV may be able to be used to play from a different standards VCR. For example, NTSC 30/525 and PAL 25/625 use very similar horizontal frequencies but different vertical rates and color encoding. Playback will be possible (in B/W at least) if the vertical lock circuitry (or the vertical hold control if there is one) on the TV has enough range. A simple color code converter can then be easily constructed using a couple of chips and some discrete parts. ----------------------------------------------------------------------------- @endnode @node 22.6 "What is a delay line and where is it used?" The question you originally asked might have been: What is this alien looking thing in my VCR? The object in question may look like a pentagonal shaped frosted glass slab with two pairs of wires sticking out of adjacent edges. What it is, is an acoustic delay line implementing a one TV line (1H) delay - around 63 microseconds (NTSC). The crystal is a shaped cavity and the polished edges are acoustic reflectors. There are a pair of piezoelectric transducers - one to launch a wave and the other to pick it up. The acoustic waves bounce around in a zig-zag pattern which increases the effective path length, thus the unusual shape. Uses in a VCR include a comb filter and tape dropout masking. The comb filter is part of the chroma circuitry and computes the sum of the current and previous video lines during recording and playback. The acoustic delay line therefore implements a delay of exactly one horizontal line. Due to the various games that are played with chroma signal phase in the NTSC-VHS system (as well as BETA and PAL), the end result is that chroma signal amplitude is doubled and crosstalk between adjacent tracks is cancelled out. This is because the chroma signal is always exactly in phase between successive video lines but the crosstalk between adjacent tracks is always exactly out of phase. The name 'comb filter' is derived from the shape of the frequency response of the comb filter - its evenly spaced spikes look somewhat like a hair comb and it is used to 'come out' the crosstalk components of the chroma signal. Another use for am acoustic delay line is dropout masking. The surface of the tape is not always perfect - bits of oxide fall off or slight dips or bumps result in momentary loss of head-tape contact. One way to minimize visible streaks in the video is to replace the lost signal with video from the previous scan line. Nothing alien about it, just not your everyday electronic part. ----------------------------------------------------------------------------- @endnode @node 22.7 "Why are there so many different design for VHS transports?" Don't expect an amazing answer - this is a set of questions. Why are there so many totally different designs to do basically the same thing? I fully understand the pressures of cost and manufacturability. However, it would seem that with VCRs, for example, every manufacturer (of which there are only a limited number who actually manufacture the tape decks themselves) and every couple model years has a totally unique design. You would think that after almost 20 years of manufacturing VHS decks, the technology would be mature. True, there have been advances with respect to quick start, HiFi, and so forth. Nonetheless, the required functions have not changed. And, for that matter, the performance of the typical mechanical deck has not improved that much in the last 10 years or so. If anything, the old designs seem to be remarkably robust. I can keep a 10 year old machine going virtually forever by replacing the rubber every few years. I am not sure that I can say the same of a modern VCR. Is it only a matter of maximizing performance at a given cost or is there something more? NIH syndrome? Maintaining control over repair parts and service? Or, use of entry level engineers who might provide a new outlook on the design? ----------------------------------------------------------------------------- @endnode @node 22.8 "Service center honesty?" After taking your totally dead VCR into an authorized service center, it is a month and still no diagnosis. When pressed, they finally 'discover' that a diagnosis has been made and the estimate is $80. The repair place is jerking you around. It should not take them as long as you have experienced to make a diagnosis - especially if they are authorized and have the service manual. They like the really easy problems like "My VCR started eating tapes last week. Is it hopeless?" 50 cents worth of rubber (idler tire), charge $50 - easy money. And they appear to be heros. To fix the electronic problems you need at least the intelligence of a carrot and time - and time is money. OK, so maybe they give a quick cleaning also. If it were my VCR, I would bitch, moan, claim poverty, threaten to report them, etc. But, get it back and fix it myself. I assume you checked the fuses. $80 dollars to fix doesn't sound like it could have been much more than a fuse. With the typical markup on parts (4:1 for small parts), those alone could easily push the bill to more than $80. The longer they hold it, the tougher the problem seems so that when presented with the (larger) bill the customer figures it is justified. ----------------------------------------------------------------------------- @endnode @node 22.9 "IR detector circuit" This IR Detector may be used for testing of IR remote controls, CD player laserdiodes, and other low level near IR emitters. Component values are not critical. Purchase photodiode sensitive to near IR - 750-900 um or salvage from optocoupler or photosensor. Dead computer mice, not the furry kind, usually contain IR sensitive photodiodes. For convenience, use a 9V battery for power. Even a weak one will work fine. Construct so that LED does not illuminate the photodiode! The detected signal may be monitored across the transistor with an oscilloscope. Vcc (+9 V) >-------+---------+ | | | \ / / R3 \ R1 \ 500 / 3.3K / \ __|__ | _\_/_ LED1 Visible LED __|__ | IR ----> _/_\_ PD1 +--------> Scope monitor point Sensor | | Photodiode | B |/ C +-------| Q1 2N3904 | |\ E \ | / R2 +--------> GND \ 27K | / | | | GND >--------+---------+ _|_ - ----------------------------------------------------------------------------- @endnode @node 22.10 "VHS specifications" Tape width: 1/2 inch Tape length: 240 meters, T120 - 120 minutes at SP speed, most common. Other lengths up to T160 and perhaps more. Tape speed: SP 1-5/16 ips 1.3125 ips 33.3375 mm/sec LP 21/32 ips .6563 ips 16.6688 mm/sec EP 7/16 ips .4375 ips 11.1125 mm/sec Track pitch: .058 mm (SP) .039 mm (LP) .019 mm (EP) Min wavelength: 1 micrometer Writing speed: 4.83 m/sec. Areal density: (SP) 34 K transitions/sq. mm Recording time: SP 120 minutes 2 hours (T120 cassette) LP 240 minutes 4 hours EP 360 minutes 6 hours Drum diameter: 2.45 inch. Drum speed: 30 rps 1800 rpm Rotation: Counter-clockwise viewed from above. Tape movement: Left-right viewed from front. Heads (typ): 2 for normal recording/playback. 2 optional for SP freeze frame/slow motion, etc. 2 optional for Hifi audio. 1 or 2 optional for flying erase. End sensing: Clear leader and trailer. Brake torque: Supply forward = 450 - 650 g-cm Supply reverse = 70 - 130 g-cm Takeup reverse = 450 - 650 g-cm Takeup forward = 70 - 130 g-cm Back tension: 20 - 25 g. Takeup torque: Play - 80 - 160 g-cm FF - greater than 350 g-cm Rew - greater than 400 g-cm Lum. Carrier: 3.4 Mhz Color sbcrrier: 629 KHz Azimith angles: +/- 6 degrees Audio bias: 67 KHz Frame length: 7.7 inches 196 mm Field length: 3.85 inches 98 mm Line length: .0147 inches .3723 mm Skew: SP - 1.5 H (sync tips align) LP - .75 H EP - .5 H (sync tips align) Color Vector A head is + 90 degree/H rotation: B head is - 90 degree/H ----------------------------------------------------------------------------- @endnode @node 22.11 "Luminance Specifications for various VCR technologies" Type Video Resolution FM Deviation Freq. Range -------------------------------------------------------------- VHS (240 lines) 1.0 Mhz 3.4-4.4 Mhz SVHS (*) (400 lines) 1.6 Mhz 5.4-7.0 Mhz BETA1 (250 lines) 1.3 Mhz 3.5-4.8 Mhz BETA2/3 (240 lines) 1.2 Mhz 3.6-4.8 Mhz SuperBETA (285 lines) 1.2 Mhz 4,4-5.6 Mhz ED BETA (500 lines) 2.5 Mhz 6.8-9.3 Mhz (*) The tape for SVHS must have a higher coercivity since the frequency is higher (information more dense) and the demagnetizing forces are greater. ----------------------------------------------------------------------------- @endnode @node 23.1 "Advanced VCR troubleshooting" If the solutions to your problems have not been covered in this document, you still have some options other than surrendering your VCR to the local service center or the dumpster. Fortunately, VCRs are among the most popular of consumer appliances to be addressed by literature that is readily available - at all levels of sophistication. If you are tackling an electronic fault, a service manual with schematics will prove essential. Some manufacturers will happily supply this for a modest cost - $20-50 typical. However, some manufacturers are not providing schematics - only mechanical and alignment info. Confirm that a schematic (not just a block diagram) is included before purchasing if possible. Howard Sams publishes Sams Photofacts service data for almost every model TV that has ever been sold but their selection of VCRfacts is limited and the newer ones tend to have strictly mechanical information. However, they are worth a shot, especially if your local large public library subscribes to the SAMs series as many do. Some of the older VCRfacts are quite detailed and complete. There are a variety of books dealing with all aspects of VCR repair. Some of these only address mechanical problems (but, hey, this covers most failures) while other are heavy into the basic recording theory and electronic troubleshooting. Your local public library probably has some of these in the electronics section - around 621.38 if your library is numbered that way. Technical bookstores, electronics distributors, and the mail order parts sources listed in this document carry a variety of these texts. Here are a couple of typical titles which I have used (there are many others and I am not necessarily recommending these above the others): VCR Troubleshooting and Repair Robert C Brenner and Gregory R. Capelco SAMS, a division of MacMillan Computer Publishing 11711 North College,Carmel, Indiana 46032 Home VCR Repair Illustrated Richard C. Wilkins and Cheryl A. Hubbard TAB Books, a division of McGraw-Hill, Inc. Blue Ridge Summit, Pennsylvania 17294 (From: Neil Preston (npreston@cctr.umkc.edu, npreston@CCTR.UMKC.EDU)) If you teach consumer electronics repair, I've run across a text that you should check out: Practical VCR Repair David T. Ronan Delmar/ITP publishers ISBN # 0-8273-6583-7 I've looked at several VCR repair books in the past, and almost all of them are very weak on the explanation of the mechanical problems in VCRs, which account for 90% of the problems. This text does an excellent job of explaining exactly how the tape transport system works in VCRs and what each part does. It has lots of photos with parts clearly identified. It assumes NO prior experience. I believe I could take a beginner student and let him walk his way through it. The table of contents pretty well describes it: 1. VCR Operations & Controls 2. Removing covers & getting started 3. Understanding the videotape path (Also with a detailed appendix describing operation of tape load shuttles, video heads & drum, capstan & pinch roller) 4. Video Cassette examination & repair 5. Troubleshooting loader and Transport Malfunctions (Includes timing!) 6. How to perform VCR Maintenance and common repairs 7. How to align tape path and make adjustments 8. Understanding basic electronics 9. How to use a multimeter 10. Electronic components 11. How to solder 12. VCR Power supplies 13. Checking motors, optical sensors & remotes 14. VCR Microprocessors & servos 15. How a TV picture is made 16. Recording on videotape 17. Beyond standard VHS 18. Using manufacturer's Service manuals 19. Common audio and video problems 20. Service considerations: The business side of VCR repairs This is by far the best book I've seen on the subject. (Please note: I have no connection with the publisher nor anything to gain by bringing this to your attention.) For basic mechanical problems, I could not have said the following any better. (From: scott.holderman@mogur.com (Scott Holderman)). One of the best I have seen is called: How To Keep Your VCR Alive (VCR Repairs Anyone Can Do) Steve Thomas Retail Book Sales, Worthington Publishing Co., P.O. Box 16691-B, 6907-202B Halifax River Drive Tampa FL 33687-6691. Tel: (813) 988-5751 This book describes in a step-by-step fashion how to repair a VCR without expensive test equipment or special tools. Fixes are described for different machines by brand & model #, and there is also a list of parts suppliers. I'm not affiliated with these people in any way - just impressed with the book. (From: cx163@FreeNet.Carleton.CA (Morton Lee Cohen)) Some of the library books that you can find in your local library, that is written in English about the repair of VCRS. One of the good books is HOME VCR Repair Illustrated. These are all in the EE section: 621.38. Author Date Title ----------------------------------------------------------------- 1 Ronan, David T. 1995 Practical VCR repair 2 Wayne, Victor A. 1992 Operating your VCR. 3 Capelo, Gregory R. 1991 VCR troubleshooting & repair. 4 Wilkins, Richard C. 1991 Home VCR repair illustrated. 5 Thomas, Steve. 1990 How to keep your VCR alive. 6 Brenner, Robert C. 1987 VCR troubleshooting & repair guide. 7 Goodman, Robert L. 1996 Maintaining & repairing VCRs 8 Williams, Gene B. 1993 All thumbs guide to VCR's. 9 Goodman, Robert L. 1993 Maintaining and repairing VCRs. 10 McComb, Gordon 1991 Troubleshooting and repairing VCRs. 11 Williams, Gene B. 1990 Guide to VCRs, camcorders, & home video. ----------------------------------------------------------------------------- @endnode @node 23.2 "FCC ID Numbers of VCRs" (This section from: William Miller, ASEET, eagle@trader.com) This is a chart used to find the original manufacturer of a VCR. Find the FCC-Listed or UL-Listed code (first few digits), then you'll see who REALLY made it! ORIGINAL UL LISTED FCC LISTED MANUFACTURER CODE(s) CODE(s) ============================================== Akai 186Z ASH Daewoo 41K4 C5F Fisher/Sanyo 403Y AFA Funai 333Z, 51K8 ADT, EOZ, BFY Goldstar 86BO BEJ Hitachi 238Z ABL, AHA JVC 439F ASI Matsushita (1) 679F ACJ, AIX, AJU Mitsubishi 536Y BGB NEC 781Y A3D, E74 Orion-Emerson 44L6, 722 A7R Philips (2) 645Y BOU Samsung 16M4, 414K A3L Sharp 504F ATA, APY Sony 570F AK8 Toshiba 174Y, 84X7 AGI, G95 1. Matsushita is the parent company of Panasonic, Quasar, and Technics 2. (North American) Philips is the parent company of Magnavox and Philco Sears model series to original manufacturer: 564 - Sanyo/Fisher 565 - Sanyo/Fisher 934 - Hitachi 580 - Goldstar 274 - RCA 626 - Phillips (Mag) ----------------------------------------------------------------------------- @endnode @node 23.3 "Determining belt, tire, and pinch roller specifications" Belts are normally specified by their cross section - square, flat, round, and their inside circumference (IC). The IC is used since it is virtually impossible to accurately measure the diameter of a belt. Assuming you cannot locate an actual part number, determine the type of belt; square, flat, or round. If you do not have the old belt, this is usually obvious from the pulleys. Most small belts (as opposed to V-belts on 1 HP shop motors!) used in consumer electronic equipment are of square cross section though flat types are sometimes found in the main drives of VCRs, cassette/tape decks, and turntables (remember those?). Measure or estimate the thickness. The IC is always specified with the belt fully relaxed. This can be measured by hooking the old belt on one end of a ruler and pulling it just tight enough so that it more or less flattens out. Read off the length, then double it for the IC. Get a new belt that is 5% or so smaller to account for the old one be somewhat stretched out. Of course, if the belt broke, measurement is real easy. Or, if you do not care about the old belt, just cut it and measure the total length. If the old belt decomposed into a slimy glob of jellatinous black goop or is missing, you will need to use a string or fine wire around the appropriate pulleys to determine the IC. Reduce this by 10-25% for the replacement. Very often the match does not need to be exact in either thickness or length - particularly for long thin belts. A common rubber band may in fact work just as well for something like a tape counter! However, there are cases where an exact match is critical - some VCRs and belt driven turntables or tape decks do require an exact replacement for certain drive belts but this is rare. Some parts suppliers make determining replacement belts very easy with the PRB system in which the part number fully codes the shape, size, and thickness. Idler tires are specified by their inside diameter, outside diameter, and thickness. Some parts catalogs provide actual size drawings so that all you need to do is match up your old tire to the picture. Since tires do not generally decompose or stretch significantly and hold their shape, measurement is usually quite easy, Pinch rollers are specified by diameter and height along with bearing inside diameter. The match must be exact so using the original manufacturer's part number is best but generic replacements are available. Parts suppliers generally provide quite complete cross references to their replacement rubber parts and complete belt kits are available for most model VCRs. ----------------------------------------------------------------------------- @endnode @node 23.4 "Interchangeability of components" The question often arises: If I cannot obtain an exact replacement or if I have a VCR, tape deck, or other equipment carcass gathering dust, can I substitute a part that is not a precise match? Sometimes, this is simply desired to confirm a diagnosis and avoid the risk of ordering an expensive replacement and/or having to wait until it arrives. For safety related items, the answer is generally NO - an exact replacement part is needed to maintain the specifications within acceptable limits with respect to line isolation, X-ray protection and to minimize fire hazards. However, these components are not very common in a VCR except for the power supply. For other components, whether a not quite identical substitute will work reliably or at all depends on many factors. Some deflection circuits are so carefully matched to a specific horizontal output transistor that no substitute will be reliable. Here are some guidelines: 1. Fuses - exact same current rating and at least equal voltage rating. I have often soldered a normal 3AG size fuse onto a smaller blown 20 mm long fuse as a substitute. 2. Resistors, capacitors, inductors, diodes, switches, potentiometers, LEDs, and other common parts - except for those specifically marked as safety-critical - substitution as long as the replacement part fits and specifications should be fine. It is best to use the same type - metal film resistor, for example. But for testing, even this is not a hard and fast rule and a carbon resistor should work just fine. 3. Rectifiers - many are of these are high efficiency and/or fast recovery types. Replacements should have at equal or better PRV, Imax, and Tr specifications. For line rectifiers, 1N400x types can usually be used. 4. Transistors (except power supply choppers) - substitutes will generally work as long as their specifications meet or exceed those of the original. For testing, it is usually ok to use types that do not quite meet all of these as long as the BVceo and Ic specifications are not exceeded. However, performance may not be quite as good. For power types, make sure to use a heatsink. 5. Switching power supply transistors - exact replacement is generally best but switchmode transistors that have specifications that are at least as good will work in many cases. See the documents on "TV", "monitor", and "SMPS" repair for further info. 6. Video heads (and lower cylinders) - generally not possible unless it is a very similar model as even the mounting is usually unique to a particular manufacturer and it may change from model to model. However, since, multiple brands may be manufactured by the same company, substitution may sometimes be possible - check a cross reference (e.g., your parts supplier's catalog) for compatibility. 7. A/C and full erase heads - may be possible if the mountings are reasonably compatible. However, there could be other unknowns like coil impedance drive requirements. The connectors are not likely to be similar. 8. RF modulators - there is a certain amount of standardization. Therefore, if you have one that fits (or you can make it fit), this is worth an attempt. 9. Motors - small PM motors may be substituted if they fit physically. Capstan motors - especially the direct drive type - are probably not interchangeable. 10. Sensors - many are sufficiently similar to permit substitution. 11. Power transformers - in some cases, these may be sufficiently similar that a substitute will work. However, make sure you test for compatible output voltages to avoid damage to the regulator(s) and rest of the circuitry. 12. Belts, tires, and pinch rollers - a close match may be good enough at least to confirm a problem or to use until the replacements arrives. 13. Mechanical parts like screws, flat and split washers, C- and E-clips, and springs - these can often be salvaged from another unit. The following are usually custom parts and substitution of something from your junk box is unlikely to be successful even for testing: SMPS (power supply) transformers, interstage coils or transformers, microcontrollers, other custom programmed chips, display modules, and entire power supplies unless identical. ----------------------------------------------------------------------------- @endnode @node 23.5 "Suggested Parts Suppliers" For general electronic components like resistors and capacitors, most electronics distributors will have a sufficient variety at reasonable cost. Even Radio Shack can be considered in a pinch. However, for consumer electronics equipment repairs, places like Digikey, Allied, and Newark do not have the a variety of Japanese semiconductors like ICs and transistors, or VCR specific components like RF modulators, idler assemblies, belts, tires, pinch rollers, video heads, etc. The following are good sources for consumer electronics replacement parts, especially for VCRs, TVs, and other audio and video equipment: MCM Electronics (VCR parts, Japanese semiconductors, 1-800-543-4330 tools, test equipment, audio, consumer electronics including microwave oven parts and electric range elements, etc.) Dalbani (Excellent Japanese semiconductor source, 1-800-325-2264 VCR parts, other consumer electronics,) Premium Parts (Very complete VCR parts, some tools, adapter 1-800-558-9572 cables, other replacement parts.) ----------------------------------------------------------------------------- @endnode @node 23.6 "Other Sources" (This section from: ac557@detroit.freenet.org (Ted C. Gondert)). Look in the Thomson (a.k.a. RCA and GE) "VCR/Camcorder Sourcebook" TCE publication # 1J9780 available from your local Thomson distributor. Publish date October 1994 (maybe newer version is out now) This book lists the most common parts for many brands and models of VCR and tells which Thomson or SK parts fit. Also has some solid state parts listed crossed to Thomsan part #. RCA VR470 uses belt #192179 or SKBK0516 and pinch roller #202113. Similar to VR450 through VR475, made by Hitachi. Service manuals for RCA/GE/Thomson are available from Thomson Consumer Electronics publications, P.O. Box 1976 Indianapolis IN (317)-267-5799. Or maybe their at 10003 Bunsen Way, Loisville, KY 40299. Microfiche for VCR is about $10. Older model series are available by the year for good prices. I bought 1985 to 1990 for $50 or so. I have the microfiche for RCA VR470. Also looked through my file cabinet and found a printed service manual for VR470 in excellent condition, only used once. Have extra microfiche set for 1985 vcr including models VLT250 to VLT470, VLT600HF to VLT700HF, VLP800 to VLP970HF. I'll sell those service manuals for a good price maybe $15 or so? (will pay for shipping). Or I'll check with local high school electronics class if they want them. Don't know if they are still fixing vcr or not, last time I talked to instructor he said it was too many problems and they were getting away from repair. Tandy (Radio Shack) can order PRB belts and have a CD ROM to look up model # belt guide. For just one set of belts, Radio Shack is much more accessible to people then mail order with $20 minimum orders and shipping/handling. ----------------------------------------------------------------------------- @endnode