Contents:
Notes on the Troubleshooting and Repair of Video Cassette Recorders
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Note: A version of this document and "VCR First Aid" may also be found at the VCR Flashbook: Interactive VCR Manual web site. The content is similar but you might prefer the style of that web page. 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.
Note: for VCR emergencies that just cannot wait, the solution may be found in the document: "VCR First Aid" and you may not need to read further. "VCR First Aid" deals with the half dozen or so acute problems that may tempt you to throw something through the window - or worse. 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.
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). BTW, if you ARE one of those individuals (and there are bucket loads) who doesn't bother (or doesn't know how) to set the clock on your VCR, there is a solution - at least the next time you need to purchase a new VCR. These machines search for a TV station that includes the time code in its transmission format (it is in the vertical blanking interval should you care) and automagically sets the VCR's clock from that information. There - no more flashing 12:00! Many VCRs have this feature nowadays.
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: * Tape loading had to be simple and foolproof using a cassette - none of this open reel stuff. * A cassette had to hold at least an hour of color video. * 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.
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. For a not too terrible ASCII diagram and additional discussion, also see the section: "VHS physical tape format". (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 azimuth 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. Azimuth 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.
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. The left and right audio channels are recorded in separate frequency bands - centered around 1.3 and 1.7 Mhz respectively. The azimuth angles for the HiFi audio heads are +/- 30 degrees which minimizes crosstalk between the recorded HiFi audio and 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.
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: * 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. * 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. * Control pulses (30 Hz for US NTSC) are recorded along the bottom edge of the tape by a stationary control head. Play: reference signal is timing pulse derived from quartz oscillator: * 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. * 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.
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.
The books listed in the section: "Popular books on VCR maintenance and repair" include additional information on the theory and implementation of the technology of video recording and VCRs. For some information on helical scan audio and data recording, see: Sprague's Technical Library.
A number of organizations have compiled databases covering thousands of common problems with VCRs, TVs, computer monitors, and other electronics equipment. Most charge for their information but a few, accessible via the Internet, are either free or have a very minimal monthly or per-case fee. In other cases, a limited but still useful subset of the for-fee database is freely available. A tech-tips database is a collection of problems and solutions accumulated by the organization providing the information or other sources based on actual repair experiences and case histories. Since the identical failures often occur at some point in a large percentage of a given model or product line, checking out a tech-tips database may quickly identify your problem and solution. In that case, you can greatly simplify your troubleshooting or at least confirm a diagnosis before ordering parts. My only reservation with respect to tech-tips databases in general - this has nothing to do with any one in particular - is that symptoms can sometimes be deceiving and a solution that works in one instance may not apply to your specific problem. Therefore, an understanding of the hows and whys of the equipment along with some good old fashioned testing is highly desirable to minimize the risk of replacing parts that turn out not to be bad. The other disadvantage - at least from one point of view - is that you do not learn much by just following a procedure developed by others. There is no explanation of how the original diagnosis was determined or what may have caused the failure in the first place. Nor is there likely to be any list of other components that may have been affected by overstress and may fail in the future. Replacing Q701 and C725 may get your equipment going again but this will not help you to repair a different model in the future. Having said that, here are two tech-tips sites for computer monitors, TVs, and VCRs: * http://www.anatekcorp.com/techforum.htm (currently free). * http://www.repairworld.com/ ($8/month). * http://ramiga.rnet.cgl.com/electronics/info.html (free large text files). These types of sites seem to come and go so it is worth checking them out from time-to-time even if you don't have a pressing need. If possible, download and archive any useful information for use on a rainy day in the future.
Proper care of a VCR does not require much. Following the recommendations below will assure long life and minimize repairs. * 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. * 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. In addition, modern VCRs are NOT built like the Brooklyn Bridge! The weight of a TV or stereo components could affect the VCR mechanically, messing up tape path alignment or worse. * 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. * 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. * 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. * Make sure all input-output video and audio connections are tight and secure to minimize intermittent or noisy pictures and sound. * 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).
"What are the 'good' and 'bad' brands of videotapes (T-120)? Are the 'extra' or "high" grades really better?" I would avoid brands you never heard of. K-mart brand, Recoton(sp), the street vendor from whom you buy Chinese food, whatever. Higher grade tapes are not necessarily worth the expense but in my experience with some like Maxell and Scotch, going one level up from the cheapest is worthwhile and results in a noticeably better picture. Only a few companies actually manufacture the raw tape stock. For what it's worth (FWIW), I usually use Scotch, under $2 for a T120 - usually in a 3 pack for $5 or $6 with one higher grade cassette. The higher grade tapes may actually be harder on the video heads due to their formulation but this probably doesn't matter for the ordinary user.. You don't need HiFi grade tapes for HiFi - any tape will work. However, higher grade tapes may last longer with higher quality results in demanding situations like 24 hour a say security monitoring. Consumer Reports does a review every so often, check back issues. I believe their conclusions were generally to buy name brands by price. Whether you believe in Consumer Reports or not, checking their ratings at least gives you an additional data point.
(From: Raymond Carlsen (rrcc@u.washington.edu)). I have not seen any "official" guidelines on tape longevity for a long time, since the Beta days. Use of old tapes will not generally ruin video heads but may clog them. Proper manual cleaning restores normal operation. Your mileage really depends on several factors, the most important being the conditions under which it's used. I've seen VCRs that can chew up a tape in one or two passes and make it unusable. High humidity and heat will cause tapes to stick to the head drum and wear prematurely. Shuttling tapes back and forth and leaving them sit in pause (on one spot) can accelerate wear. Under ideal conditions: clean machine in good alignment running a tape from beginning to end without stopping is as good as you're going to get. Alignment tape manufacturers used to indicate expected life as the "number of passes". No significant degradation in 50 passes, but after that, dropouts become obvious. Maximum life is 200 passes. At that point, the tape is starting to break down with oxide particles being shed onto the heads (actually happens with all tapes to some degree) causing head clogging. With tapes of any age, a liquid spill such as soda pop ends the game right there. It can be cleaned, but unless it's your precious home movies, forget it. I would use a tape until the dropouts become annoying. Dropouts are places on the tape where the oxide is missing. You'll see them more at the beginning of a tape where it's mechanically stressed by loading and unloading. A lateral scratch on a tape (caused by buildup of gunk in a VCR) will show up as a 3 or 4 line continuous dropout somewhere on the screen. Look at some heavily used rental tapes and you'll get the idea. So, bottom line: use it until it shows it's age. :)
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: * 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. * 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. If you want some guidelines, see the next section: "Sample VCR preventive maintenance schedule". 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: * 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. * 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. * 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 parts replacement", 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.
Here is an example of the recommended inspection, lubrication, and
replacement schedule for a typical VCR as provided by the manufacturer.
This is from the Sams VCRfact for a particular non-HiFi RCA VCR. I am
providing this for information only and am not necessarily recommending
these or other similar hard and fast rules for VCR preventive maintenance.
It is not clear here what a 'tape' is though the comments that go along with
this table seem to indicate that it means a T120. However, parts that deal
with tape loading are affected not by how long a tape is played but by the
number of loading cycles. Wear on the video heads, on the other hand is
strictly a function of play/record time. Wear of the A/C and erase heads
depends on both time and tape speed. Thus, these are additional reasons
not to take the numbers below too literally.
After What to do Which parts
------------------------------------------------------------------------------
250 tapes Clean A/C head, capstan, erase head, pinch roller,
impedance roller, supply reel table, takeup
reel table, video heads.
500 tapes Replace Video heads (upper cylinder).
750 tapes Replace Pinch roller
1000 tapes Grease Loading cam gears, impedance roller shaft,
roller guide tracks.
Oil Supply reel shaft, takeup reel shaft.
Replace Reel belt, loading motor belt, main brake
spring, main brake arms (left and right).
2000 tapes Replace A/C head, erase head, supply reel table,
takeup reel table.
2500 tapes Replace Cylinder unit.
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