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Notes on VCR Troubleshooting and Repair INDEX V.
Chapter 10) GENERAL CONTROL PROBLEMS

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:
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.
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.
If (2) doesn't do anything, try several turns counterclockwise instead.
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" may have resulted in an overshoot to a bad mechanical state and without cleaning or replacement, the same thing may happen again.

10.2) VCR attempts to play non-existent cassette

You turn power on or just plug in the VCR to the AC outlet and it goes through the whirring sounds of playing a cassette - but there is not cassette present. However, first try unplugging it for 30 seconds or so and plugging it in again. The microcontroller may just have had a bad day and gotten confused - either a bad reset or a power glitch.
Assuming this doesn't help:
This could be due to a faulty end sensor or a bad LED or light bulb that provide illumination for the end sensors.
If either sensor's output is the same as when a cassette is present (blocked), it very likely that the microcontroller will be confused. In some designs, this is indistinguishable from a cassette actuallly being loaded.
If the 'cassette in' indicator is on, then this is likely.
BTW, if a VCR uses an actual light bulb for that central light source and it is not lit when you attempt to load a cassette, it is burnt out. The LEDs used in most modern VCRs are IR and invisible, however.
With somewhat similar symptoms, it is also possible that the VCR is not able to complete the startup initialization due to a slipping belt, gummed up lubrication, or other mechanical or motor problem. The clincher would be if you manually load a cassette (by turning the appropriate pulleys, etc. with it unplugged) and it then plays the cassette properly and acts normally until you try to eject. However, don't try this unless you are sure of how the mechanism works as it is easy to cause damage.

10.3) 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". Failure of the Mode Switch is a very common problem with numerous VCRs of many makes and models.

10.4) 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:
Tape unloaded and cassette out.
Tape unloaded and cassette in.
Tape half loaded against A/C head but not around drum.
Tape fully loaded around drum and roller guides at V-stoppers.
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".
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.

10.5) 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.

10.6) 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".

10.7) If this is not enough for you to get the hint

Here is a true story of forced eviction of a tape and the consequences. :-( This teaches you two lessons: Don't use violence to remove a stuck cassette and mark all gear, lever, sliders, etc. timing relationships before you disturb anything! (From: AL (kb8wcq@tir.com)).
"I have a Panasonic VCR (model PV-4820) that will not acknowledge tapes. The original problem I found was in the power supply. I replaced all the electrolytic caps, and the PS now works- all the outputs measure OK and the display and tuner controls seem to work OK.
But once the PS went bad, it would not take in tapes, so the owner decided to force one in. He sheared half the teeth off of the 'link gear', which I replaced, but it still will not accept a tape. I can manually push a tape all the way in, with some resistance, until it sits down on the reels, but it is not acknowledged in any way. If I don't hold it down, it springs back out." It sounds like you possibly failed to retime the link gear in relation to the rack gear on the loader assembly.
If that's the one I think it is and you have not timed one (of course this is something the average person does, say once a week? :-) --- sam) before, you probably should get the manual. Or try this: Remove the carriage assembly, turn the VCR on its side, press and hold the little white change lever (bottom side, near the solenoid), manually turn (CCW) the large belt-driven pulley until the mechanism is in the full eject position, note the position of the link gear, turn the large belt-driven pulley in the opposite direction until the link gear makes exactly one revolution, re-install the carriage (in the eject position) making sure the carriage gear and the link gear mesh properly. Other than that it's pretty simple... Assuming of course nothing was disturbed with the gears below the deck, and that the link gear, mode switch, pressure roller lift cam, etc', are in their proper position. Sounds simple enough! --- sam :-)

10.8) 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.
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.
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.
Ensure the tape guide assembly is fully retracted by physically turning the appropriate gears.
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.
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.
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)

10.9) 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".
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.

10.10) 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. 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.
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.
Best bet is to check your instruction manual (you can locate your user manual, right???).

10.11) 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.

10.12) 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 lightning 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". 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.

10.13) 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.


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