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: "Types of motors in VCRs". 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.
"I've got one of the Damark ones and it does work for Macrovision protection, depending on the input deck. My 10 year old Panasonic VHS Hi-Fi (No MTS tuner, Dolby(tm) B linear stereo non-Hi-Fi audio too) works fine as an input deck, while my new JVC Hi-Fi doesn't. Why some input decks work and others don't is my question. Anyone know? Is there added circuitry that the newer decks have to defeat the stabilizer boxes?" (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). JVC owns the patent for VHS. JVC has made a deal with Macrovision that from a certain date in the past *no* VHS recorder licensed by JVC shall be able to record any video signal that contains Macrovision's copy protection pulses. Any video recorder from before that date (VHS or other) might well work OK on the altered video signal! The copy protection pulses upset the video AGC and H-sync. TV's usually don't have a video-AGC. Thus the whole idea of the Macrovision method is to disturb the video AGC that is inside every VCR - the manufacturers even *must* make the video AGC sensitive to those pulses! In the TV, the horizontal sync processing may be disturbed by the Macrovision pulses. Indirectly that also disturbs the DC clamping circuit. So you may see horizontal phase as well as brightness disturbances at the top of the picture. The stabilizer box removes the extra pulses and makes it into a normal video signal again. No VCR should ever know the difference, so they should all record properly again. At the same time, all TV's are required to ignore the copy protection pulses. As a TV-designer I can tell you that this is sometimes far from trivial. Not in the least because in the beginning we were not included in "the deal". There may be TV's around whose brightness and/or sync will be disturbed by the Macrovision pulses. Officially, this is the reason for existence of the stabilizer boxes: to view better, not to copy better. Unofficially, they are sold for copying, of course. Keep in mind that the Macrovision 'standard' (pardon me) has been improved several times. Old decoders may not be able to cope with newer tapes. In order for the decoder to key out the pulses in the vertical blanking interval, it must first synchronize properly itself. That process too may be disturbed (by extra pulses on newer tapes to older decoders). Those Macrovision a**holes are smarter than you think. Unfortunately, their signal may also disturb some TVs which are used legitimately. And then it becomes *our* problem too. The next step will be that digital-TV decoders will output an analog TV signal with Macrovision copy-protection pulses so that you may watch but not record your pay-per-view program. Same problem, same solution ... And I thought that PAL/Secam/NTSC were *standards*, sigh ...
(From: Mark T. O'Bryan (firstname.lastname@example.org)). Look at it this way. The reason that you see changes in brightness is that the "protection" signal that is added makes the unit's AGC (auto- matic gain control) think that the level has shifted, when it hasn't. So it adjusts to compensate. So if you have an older VCR without AGC (or a mild application), it may not be affected as much (or at all, after passing through a "stabilizer" box). If the sensitivity of the AGC is high (like it is on most JVC's) and the response-time is short, any small amount that leaks through will still cause problems. For those familiar with the electronic circuitry in VCRs, both the time constant in the RC circuit for response-speed, as well as the AGC sensitivity can be adjusted by manipulating simple resistor values. I don't have any specifics on this (and it varies on different machines), so don't bother asking for it :-). But at least you now know why some decks react differently.
"I've just started to use the closed caption feature of my TV and have a problem with pre-recorded video tapes, and am wondering if it could be the VCR. The problem is simple: about half the tapes I've watched displays the CC information incorrectly (many missing characters and/or lines), or will not display it at all. Sometimes I can improve the CC display by adjusting the VCR tracking to the point where the picture starts to become fuzzy, but for the most part it remains garbled and uncorrectable." Of course, as with so many other problems, poor quality or well worn tapes can result in erratic closed caption decoding. Therefore, I would not recommend diving into the bowels of your VCR before trying out some other tapes. (From: Thomas D. Kite (email@example.com)). Sounds to me like the head switching point is too far down the screen, i.e. the point at which the VCR switches between the video signals from the two heads is too late. You can check this if you have a TV with vertical hold. Set the hold to give a stationary or slowly rolling picture so that you can see the head switch, which will appear as a tearing of the picture. This should occur during the blanking period, but I suspect that your VCR is switching sometime later. If so, open it up and look for a preset on the main board labeled 'Head SW PT' or something like that. Twiddle it so that the tearing backs up the screen into the blanking part (again, do this while the picture is rolling slowly). Hopefully, this will mean your VCR has done its switching by the time it gets to Line 21, and the CC information will be intact. (From: Richard Beeler (firstname.lastname@example.org)). This could be Copy Guard on tapes interfering with the closed caption decoding. We had one that was doing the same thing on some pre-recorded tapes and not others. We finally had to add a 'video stabilizer' between VCR and TV - that corrected the problem.
The clock display is dark but other functions are normal. Your VCR probably was made by Hitachi (Sears is one of several brands that may be manufactured by Hitachi). If so, probably your DC to DC converter went bad. Please note that the the converter is close to the front of the VCR and not on or near the main power supply board. Also check the IC protector (possibly ICPN5) as it may have blown. You should also replace the two 47 uF 50 V and the 100 uF 35 V capacitors near the DC to DC converter. These are known to go bad resulting in failure of the DC to DC converter. Complete repair kits are available from suppliers like MCM Electronics. These will include all components likely to have gone bad. For some models: (From: Sire Johnathan (email@example.com)). Behind the Channel selector is an upright PCB. on the upper inside corner find a 1/2" sq. transformer can with top hole and slotted core adjust. The schematic nomenclature is T101 or T102. Next to it, find a TO-220 power transistor. Replace the Pwr Xstr, filter caps in secondary side rectifier with DOUBLE the voltage ratings, and a small choke (L1?) that feeds primary power to the power transistor (fuses open). When working properly, current draw through primary circuit should be less than 200 mA.
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? JVC VCRs of that era tend to shed parts in the tape loading mechanism - easily fixed. Unless it is a serious electronic problem (there is a minor one which results in similar symptoms - see below), a service manual may not help. And even then, it may not have the information you need. Check the roller guide assemblies (see the sections: "Parts of the tape transport in a VCR" and "General tape path alignment problems"). There are two types of failures that occur frequently on various JVC models: * 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 guidepost, 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. Just popping it back in, even if the post appears snug, will result in a callback. 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. Of course, it may already be too late :-(. * If a roller guide does not seat fully against the V-Stopper (the end piece) but the brass pin has not fallen off or loosened, 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. Clearances are really tight so if the screw head sticks up more than a mm or so, it will restrict movement of the roller guide assembly resulting in loading and/or unloading problems. Alternatively, a dab of plastic cement may work. In either case, tape path realignment should not be needed. To get at the bottom of the roller guides or hinges, you will probably have to convince the VCR to start loading a tape and then pull the plug just as the mechanism is in a position where you can get to it. * Another common cause for a band of video noise at the top or bottom of screen on some JVC models: Defective capacitor (may be C6, 3.3 uF, 50 V) on drum motor resulting in bad PG pulse. It looks like a tantalum cap but a regular electrolytic should be satisfactory. Even Radio Shack will likely have a replacement. In some severe (or shall we say, strange) cases, good and bad/no video may occur randomly each time the VCR enters PLAY mode but will remain that way until the tape is unloaded. (From: Mark Shoberg (firstname.lastname@example.org)). When replacing the 3.3uf cap on the motor board (this is for the older bottom mounted types) just cut away the plastic piece covering it a little bit. This way you don't risk damaging the video heads and it is easier as well.
A number of Panasonic and other Matsushita brand clones use a switching power supply which has a couple of common failure modes. * 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. * 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 C14 or C21 (depending on model) which is 1 uF, 50 V. * The primary and secondary 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 under "Various Schematics and Diagrams". Some of the sources listed in the section: "Suggested Parts Suppliers" sell power supply rebuild and capacitor kits. Unless your power supply is missing, one of these kits will probably fix it - and you need to know is how to solder!
Symptoms include anything from erratic behavior to acting totally dead. There are many RCA models for which the info below applies. (From: Ken Koskie (email@example.com)). This may be one of the RCA VCRs plagued with intermittent diodes. RCA recommends replacing the following diodes; D108, D109, D110, D112, D114, D1103 and D1104. Their part number for the diode kit is 201066. "I am currently working on a GE VCR Model VG-4016 with the following problem. When the tape is inserted it loads fine the head starts spinning but it doesn't play because the capstan is not turning. If you push play a second time it start to play but is in the X2 mode so its going to fast." (From: Frank Fendley (firstname.lastname@example.org)). Common solution for this - replace D108, D109, and D110 - even if they test good with a meter. ECG125 works well for this (2.5A/1000PIV). While you are at it, also replace D105, D106, D111, D112, D113, D114, using the same replacement. Samsung must have purchased 40 billion bad diodes when they built these units. Funny thing is, they almost always test OK with a meter but replacing them fixes the problem. Apparently they go open under operating voltage, but not under the lower voltage provided by a meter. Alternate solution (fairly uncommon) - replace IC201. (From: Mark Z. (email@example.com)). If this model is the type I think it is, there is an open diode along the inside edge (toward the mechanism rear) of the top circuit board. There is actually about 7 diodes which tend to go bad in these due to underrating. Five are in the area I mentioned, that is two along the edge at the middle of the board, and three further back, and two are located under the power transformer. Other problems, such as no display or no power, will occur if any of the others go bad. Suggest you replace them all; Any decent 1N4007 or such will do fine. Radio Shack has "2.5A 1KV" diodes which would be fine. For some RCA VCRs with somewhat similar symptoms: (From: TVman (firstname.lastname@example.org)). For the RCA VR321 which appears dead, clock display may come on after a few minutes, Q1 runs hot: Replace: C09 (22 uF, 16 V) non polarized capacitor in power supply.
Two words: Mode Switch. Whenever you have problems that seem to come and go or go away temporarily with repeated attempts to play or enter some other mode, the problem is very likely a dirty (or worn) mode switch (may be called the 'mechanical state switch' by some. The chassis of Sharp VCRs come in several flavors. Here is a description of two of them with respect to getting at the mode switch: * Newer models (e.g., VC-A607) have the mode switch as part of a modular loading motor assembly. This is found on the top in the far right corner of the transport. It is mounted by 3 screws, easily removed. There are no timing relationships to get messed up as long as you don't try to cycle the mechanism while disassembled. Therefore, it can be removed and replaced without concern for gear timing. The link between the mode switch and drive gear is keyed so it will go back together properly. To access the mode switch, unplug the connectors, remove the single belt that drives the eject mechanism, and remove the 3 screws. It should now be possible to detach the entire assembly. Underneath, you will see a disk with a keyed center hole - this is what must be replaced with the same orientation as it was before removal. The disk snaps off easily revealing the tracks and contacts of the mode switch. Thoroughly clean and slightly increase the spring pressure of the contacts. Replace in reverse order. Make sure the post slips into the keyed hole as you replace the assembly and double check that it is seated before tightening the screws. * Older models (e.g., VC7864U) are a bit trickier. The mode switch on these models is sandwiched between the loading gears and a mounting plate - all parts of what I will call the 'loading gear assembly' underneath the tape transport. To access the mode switch, this entire unit needs to be removed and partially disassembled. The gears operate the roller guide loading mechanism, and a couple of cam operated levers which are conveniently hidden when it is removed or reinstalled. It is driven by the loading motor via a couple of idler gears. Timing marks: There is at least one critical timing relationship that needs to be preserved when the loading gear assembly is removed. I recommend that you put your own timing marks on all gears before loosening the 3 screws that anchor this unit. You will need to unsolder 4 connections as well before it will come free. Once the bottom of this unit is accessible, the mode switch can be snapped apart and cleaned. I believe this is best done with the VCR in the unloaded and ejected state. However, there are still a couple of levers that will need to engage properly when the loading gear assembly is replaced. These press on internal cams that are hidden when everything is together. Much fun.
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. Remove the half loading arm by unscrewing the locking nut. Count the revolutions of the nut as you do this since it sets the height which is somewhat critical. Clean the bearing and shaft and then lubricate it with a drop of light oil or a dab of light grease. If you forgot to count the turns or the nut had originally loosened up, just center its height within the range over which the tape moved stably past the first fixed guidepost and/or A/C head. Then confirm reliable loading and unloading with several different tapes. Try using forward and reverse search to assure that the tape isn't moving up or down on the guides. Make sure there is absolutely NO tape edge damage. 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 bit of cleaning and drop of oil. (From: Sire Johnathan (email@example.com)). I recall well from counting turns until that elastic nut lifts off the stud is very repeatably 6.5 - 6.75 turns. Checking it with the Sony height specs is always within limits. Don't forget to check the smooth running of tape over this 1/2 load pre-threading guide pin in the reverse scan direction. The tape should maintain same height when changing rapidly between FWD SCAN and REV SCAN. A worn conical pinch roller can cause tape height shifting and tape edge-rippling or top-slacking because the pinch roller becomes the primary tape guide in REV SCAN. Changing quickly between REV SCAN & PLAY modes while monitoring normal linear audio treble and tracking can reveal any mis-skewing of the tape path as it 'returns into the groove' in PLAY mode. Sony pinch rollers are notoriously short-lived causing most tape edge-rippling and mistracking. BEWARE of 3rd party substitute parts as they are frequently out of tolerance and poor bearings necessary for Sony mechanisms.
(From: VCRMonthly (firstname.lastname@example.org)). Later Sony VCR's have "emergency" codes that show up in the Fluorescent Display on certain failures. The code shows up in the "seconds" position and they are as follows: Code Problem ----------------------------------------------- 00 Normal. 01 Abnormal Take-up reel rotation. 02 Abnormal Supply reel rotation. 03 Abnormal drum (head) rotation. 04 Abnormal forward cam motor rotation. 05 Abnormal reverse cam motor rotation. 06 Abnormal cassette loading. 07 Abnormal cassette unloading. Play a tape until the VCR shuts off and then check the failure code to help diagnose the problem. These codes are cleared when AC is removed or when another function button is pushed. Some Sony VCRs may use the error coding summarized below: (From: J-S Ferreira (Gal@microtec.net)). Error Code Block Problem -------------------------------------------------------------- 00 No error 01 - 09 Control motor (encoder) Unable to detect the position 10 Mechanism Loading not completed 11 (deck) Unloading not completed 12 " No eject 13 " End sensor fault (take-up side) 14 " End sensor fault (source side) 15 " Dew detected 20 Drum Drum motor won't rotate 21 " Drum servo not locked 30 Capstan Capstan motor won't rotate 31 " Speed not locked 40 Reel Take-up reel FG not locked 41 " Source reel FG not locked 42 " Measure abnormally ended (whatever this means)
A typical set of symptoms and questions: "The capstan motor on my Sony VCR has lost the war and is in need of replacement. Based on my Dejanews search on this topic, this is evidently not an uncommon occurrence :(. My local repair shop diagnosed the problem for $30 and gave me a $200 estimate to fix it. 3 questions: * Is this reasonable? * Does a capstan motor for this VCR really cost $95? * Given that I'm fairly handy with electronic repair, but inexperienced with VCR repair, is this something that I should attempt without a service manual? In other words, is this a particularly difficult or tricky repair? To satisfy the curious: the symptoms were a jittery picture on playback of tapes. The problem began with playback in EP mode only (the picture would freeze and hi-fi audio would "ratchet" as though the tape had come to a halt). It progressed until this started happening in SP mode as well. The problem got much worse the longer the unit was running (or the farther into a given tape I watched...)." (From: Bob Groger (BobG1@msn.com)). This is a common problem, but you don't need to replace the motor! Sony sell a new bearing assembly for about $25. There is a service bulletin out on this. The bearing housing bends after a period of time from pinch roller pressure. The new one is much stronger. Quick but temporary cure is to grasp the top of the bearing housing with big pliers and bend slightly towards pinch roller. This is NOT a guarantee! (From: ZMachar780 (email@example.com)). They have a lot of bad capstan motors on these. The bearing collapses a little, then the flywheel scrapes on the drive coil. Sony sells a replacement bearing assembly which would save a few bucks over a cap motor, but frequently the capstan shaft is worn anyway and should be replaced. Sony will ID the part number(s) and sell you the part directly (on a credit card). Call them at 800-282-2848. (From: Willis Chung (firstname.lastname@example.org)). This is the classic Sony capstan motor bearing problem. The capstan motor is a direct drive unit with a large flywheel/magnet assembly mounted just below a set of flat coils. The bearing that the capstan turns through is also part of the bracket that supports the motor. With time, the bearing wears out, allowing the capstan to tilt ever so slightly. This tilt causes the capstan flywheel to come into contact with the coils, causing a scraping sound, intermittent pauses, and eventually causing the motor electronics to die. Stop using the VCR now to prevent damage to the motor's electronics. The capstan motor bearing can be replaced without having to replace the entire motor. The bearing is available direct from Sony for about $12, but the entire motor costs about $45-$55. For the SLV-575, the part number for the bearing assembly is X-2625-269-1. However, replacements for other VCRs have different part numbers - best to check before ordering. Replacing the bearing is straightforward, and anyone can do it (well just about anyone!). 1. Remove top and bottom covers with machine unplugged 2. Unplug connector cable to capstan motor circuit board 3. Unscrew motor from chassis (3 screws accessed from top of chassis. 4. Remove capstan flywheel and shaft from motor (just pull to separate it from the rest of the motor) 5. Unscrew capstan bearing from motor assembly (3 screws) 6. Assembly is reverse of disassembly. 7. Play junk tape to see if there is any folding of the upper or lower edges of the tape, especially just past the capstan. You may need to make some adjustments to the metal guides to the right of the capstan. 8. Make comments to people around about cheap motors, using harsh language. The repair is easier to do than to explain! (From: David A. Sanders, II (email@example.com)). The bearing part number for the Sony SLV-R5UC VCR is X-2625-356-2. The motor part number is 8-835-350--02. Check the winding on your motor. Many times when the bearing fails, it allows the magnet assembly to rise, which in turns starts to cut into the windings.
(Portions of the following from: firstname.lastname@example.org ((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.
(From: Tony Buffone (uproc@Aol.com)). On the subject of the funai type rubber bumper problem I would like to give an additional symptom of that problem. After repairing hundreds of these units one goofy symptom I've found is the fact that customers may complain that the machine will eject a tape that is fully rewound and will play a tape if it is anywhere else on the tape. The FF/REW problem may or may not show up at this time. Also note that the best cure is the original part from symphonic. I have found that generic bumpers from MAT or MCM for example have cost me callbacks because there just not cut perfectly. (From: Matthew L. Kruckeberg (MKRUCKEBERG@pol.org)). I have run into a few of these Funai mechanisms where the replacement rubber bumper is too thick causing the mechanism to lock up in various positions. If you still have the original one try reinstalling it backward and see if your problem goes away. I would not recommend turning the bumper around permanently since the repair is short lived due to deterioration of the rubber but it will generally work at least for test purposes.
"Has anybody had any experiences with a Zenith VR2422HF VCR having auto-track problems with certain rental tapes? This is the second one I've had in the shop where it will switch back and forth between sp and SLP speeds. has anybody seen any mods or heard anything?" This is a common problem with certain Zenith VCRs. It is caused by the copy guard present on certain rental tapes. Zenith will modify these VCRs at no cost. The modification inverts the sync pulse by adding a transistor, a resistor and modifying the circuit board. If the model number starts with VRJ or VRL (possibly others as well), this is likely to apply. If you don't want to do the modification yourself but really want to sound like you know something, suggest that the problem is covered by Zenith Field Service Bulletin #94-16 :-). Two very similar modifications follow: (From: Guitarzan (email@example.com)). Locate IC201 on left of top circuit board and IC 202 on right. Cut the trace between IC201 pin 56 and IC202 pin 17. I've found it easier to remove the wire jumper directly beside pin 56 as this leaves a place to mount the transistor. Install a general purpose NPN transistor (ECG123A, Zenith 921-2161 or 921-2134, or 2N2222) with base to IC201 pin 56, emitter to ground, collector to 10K 1/4 W resistor, other end of resistor to W2H5, or another +5 V source. The current drain is very minimal so pick the most convenient source of +5 V. All this does is invert the servo pulse and keeps the circuit from becoming 'confused'. If only it would do the same for me. Fire it up and all should be well. Try an EP tape, if its installed incorrectly, EP won't track at all. (From: Brian Hughes (firstname.lastname@example.org)). Required parts: Small signal NPN transistor (ECG85, ECG2357, KRC103M), 10K 1/4 W resistor. Locate IC 201 on the main circuit board, cut the trace between W2C4 and IC201 Pin 56. Solder resistor between W2C4 and W2H5. Solder transistor as follows: Base - IC201 Pin 56, Collector - W2C4, Emitter - IC201 Pin 5. Insulate all exposed leads ( I like hot-melt glue, it secures things in place as well.) Finis. Why it works: Many pre-recorded tapes have timing marks inserted in the control-track signal. These extra pulses confuse the servo circuit in these machines. This modification inverts the signal before it reaches the servo so that it is not detected.Go to [Next] segment
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