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SERVICEMAN'S LOG Stop me if you’ve heard this one This month’s notes are on a slightly different tack than usual. Almost by accident, they finished up as a resume of all the dreadful things that happen to, or are done to, video recorders. Take note; it might happen to you. It all started with the story in the October notes, about the ballpoint pen pushed into a Philips VR6448/75 video recorder – presumably by one of the owner’s children. That incident caused considerable trauma all round. Inevitably, this story came up at an informal gathering with a couple of colleagues, who are aware that I write these notes. And just as inevitably, it prompted memories of all the strange things that had been found in video recorders, some of which I have listed in previous notes. One I recall was a 20c piece, which caused a lot of trou­ ble. And then there was the machine which had 54  Silicon Chip been stored in a garden shed and had become home for a family of ants. Between us, we came up with quite a list. Toys being “post­ed” are common. And there was another ants’ nest story, from a colleague this time. The owner of that machine lived in a bush­ land setting in what might be described as a rather elementary dwelling. Fortunately, the infestation wasn’t very severe and the machine was salvaged without much trouble. But it could have been a lot worse. Cockroaches are another common foreign body. They don’t do much damage as long as they keep clear of the moving parts. But when they do tangle with them, they can make an awful mess. Some of the more unusual items found in video recorders have been wedding and diamond engagement rings, false finger nails (the mind boggles), fruit cake and sweets! The wedding and engagement rings were found by a colleague in two separate machines. There must have been a couple of inter­ esting stories about them but we will never know. My colleague was working on a subcontract basis for another firm and he never heard anything more about them. Another frequent offender is the cassette label which has lost its glue and fallen off, jamming the reel and loading mechanisms. And then there was the VCR that came in with no less than three tapes jammed inside! The owner was under the fond impression – I never did find out why – that as each tape was played, the machine automatically ejected it from the rear. How do you get three cassettes into one machine? With great difficulty, might be smart answer. But this owner managed it. Granted, this particular machine lent itself to such abuse more readily than most. As it came in, there was one cassette correct­ly loaded, another which had been forced in on top of it, and a third which was protruding from the loading opening. It was the latter that apparently alerted the owner to the fact that someth­ing was wrong! That story just about exhausted the “foreign bodies” theme but led quite logically to other common VCR faults. And I re­alised that many of the common faults we tend to take for granted had not found their way into these notes, either at all or for a very long time. So here are a few; some from me and some from my colleagues. A common complaint One common complaint in some machines is caused by attempt­ing to load a cassette upside down or the wrong way around, which bends or breaks the cassette door unlock lever. This lever en­ gages a small square plastic pin immediately behind the cassette door flap, on the right-hand side. (Pushing this pin allows the door to be opened manually, exposing the tape – a common trick where damaged tape is suspected). So, if the unlock lever is damaged, the cassette door will not open, preventing the set from accepting a cassette. It goes in, but only the left side goes down; the right side cannot, as the door is still closed. One machine that I encountered quite recently was a varia­tion on this theme. The customer brought in his machine, a Na­tional NV-370-A, along with a cassette, an NEC HDx E-240 made in Korea. And it was a virgin tape, just removed from its plastic wrapping. His problem was that the machine would not accept it. It could be pushed in and, initially, everything would appear to be normal. But then, after a few seconds, the machine would eject it. On closer examination, he realised that the entrance flap had not closed completely but he had no idea what this meant. However, he had another machine available – an older Sharp – and this accepted the cassette without hesitation. Ergo, the fault must be in the National. Had he tried any other cassettes? No – he had not wanted to force the situation for fear of causing further damage. It was a commendable attitude, even if it turned out to be an overreaction – which in fact it was. I tried the suspect cassette in the National and it behaved exactly as the owner had said. Then I pushed in one of my own tapes and it loaded immediately, as did a second and a third. This removed any lingering doubts; the fault was in the cassette, not the machine. But why? And should the cassette go back to where it was bought? This presented problems. It had been bought some time ago and the purchase docket had long since been lost. And, in any case, there might be some difficulty proving that the cassette was faulty. Then I had an idea. I had another customer’s machine on hand, an older, top loading type. I tried the cassette in this and it baulked also, but in a different way; the loading cradle would not go right down. However, the top loading arrangement made it possible to see more clearly what was happening and it was obvious that the cassette door was not opening. And I was able to get a small probe down the side of the cradle where there was an intermediate lever, used to engage the door opening pin, and exert slight pressure. And that did it – the door opened and the cradle could be pressed home. I took the cassette out and tried another trick. There was a small amount of lateral slack between the cassette and the cradle and I loaded it again with the cassette pressed hard to the right. Success again; the cradle went down quite readily. I then tried the same trick with the National, pressing the cassette hard right as I pushed it into the opening. Once again, it loaded normally. So what was causing this problem? Apart from the obvious fact that the door release pin was not being fully activated, the basic cause remains a mystery. I suspect that it is a plastic moulding problem. Either the die was faulty – unlikely – or the plastic was sufficiently unstable as to permit some shrinkage – which seems more likely. More importantly, what to do about it? We mulled over various ideas aimed at ensuring that the cassette was held hard right on entry but they all had disadvantages. In the end, the customer decided that the easiest way was simply to remember to push it hard right on loading – and to mark it in some way as a reminder. Dirty video heads Another common problem is dirty video heads. I find it almost impossible to convince people that dirty heads are almost always due to faulty tapes and that, after I have cleaned them, it is essential that they locate and discard the tape that caused it, otherwise the same thing will happen again. It should not be that hard to understand that the heads protrude above the drum surface, are in contact with the tape, and spin at 1500 RPM. Nor should it be hard to understand that there will be an awful mess if the tape surface isn’t perfect. But it’s no good; within days they are back saying it is doing exactly the same thing – and you both know the same tape was tried again. Nowadays, I try to be philosophical about it and just clean it again, if possible in front of them. I always advise December 1995  55 clients to buy quality tapes and play them in the “standard play” mode. After all, you get what you pay for, and expecting cheap tapes to perform well in “long play” mode is pushing the system to its limits. Normally, I clean the heads by very gently rubbing them with oil-free acetone (available from the local hardware store) and a lint-free cloth. If you have ever seen what acetone can do to tape, you will appreciate how powerful it is. However, there have been times when the dirt is so compacted in the video head gap that even this would not shift it. On one occasion, many years ago, I had an Akai VS2 come in with no picture on play, the snow effect being muted by the set’s circuits. I tried cleaning it with acetone very aggressively but to no avail. I was about to condemn the heads when I remembered a Maxell tape cleaner in the waste bin, one that I had fished out another machine earlier. I had never been very keen on these gadgets – I’m still not for that matter – but, with nothing to lose, I tried it on the Akai. Amazingly it worked. So 56  Silicon Chip now, as well as the acetone treat­ment, I resort to a tape cleaner in the most severe cases. And I found quite by accident that two abrasive tape cleaners have a very useful capability – Maxell T-CL and TDK TCL-11 tape cleaners have the ability to record a video signal. The picture quality isn’t the best but a video image on the tape can provide a very useful guide. It means that, when you are cleaning dirty heads, you need only play the tape until the picture reappears; you don’t have to flog it until it has cut its way right through the heads. Unfortunately, I haven’t seen Maxell tape cleaners avail­able anywhere recently. Also, the T-CL version has been replaced by the E-CL type, which doesn’t record nearly so well, which is a great pity. Similar symptoms One problem with servicing VCRs is that many of the symp­toms are very similar, particularly snow and lines, and those involving tracking. And, because most people don’t see these somewhat similar symptoms very often, they are not good at de­scribing them. As a rule of thumb, lines and tracking faults are normally confined to mechanical tape path and servo electrical areas, while snow is indicative of head and head amplifier failures. But occasionally it can be other areas, such as power supplies, that give strange effects. One clue for these less common faults can be the time taken before the symptom occurs. If it takes some time for the fault to either come good or go bad, it implies that heat can be affecting a vital component. The Sharp VC488X, Philips VR6940/75, and Marantz 740A early series of hifi video recorders are a case in point. These ma­chines are packed with electronics, with at least three or four PC boards stacked one above the other, resulting in poor air circu­lation. The power supply, in particular, is the cause of most of the heat, and the power regulator board (PWB) is one the victims. More particularly, it is the electrolytic capacitors which dry out and upset the various rails. Two 1µF 63V capacitors, C962 and C963, and sometimes C970 (100µF), can cause the machine to perform as though the heads are dirty or very worn, with snow and smearing video. Not only is it sometimes difficult to be sure about these components but, when they are suspected, it is just as tricky to replace them, as access to this board is appalling. The power supply PWB-P is tucked away deep down in the left rear corner of the chassis and, even after removing about umpteen screws and removing the two head amplifier modules, it is still very diffi­cult to pull the circuit board away from the wiring harness. In fact, it is necessary to bend part of the metal board support, if you want to complete the job in a reasonable time. When the board is finally extracted and all the connections unplugged, one is then faced with about 20 electrolytic capaci­ tors (C952-C972). So how many should be replaced? The main cost of the repair is the labour involved in removing and replacing this module and it is false economy to risk doing this again in a hurry. I normally replace all the physically smaller sized capaci­tors (about 15) up to about 220µF with higher temper- ature (105°C types, such as the TKR series). I also rework all the solder joints before reassembling the beast. Note: care must be taken to properly refit the chassis screw at the rear of the head amplifi­er board, otherwise there is a risk of losing the 9V rail, marked +PB 9V on the board. Other head type problems, like snow, can be attributed to drum/cylinder motors which lock out of phase, usually intermit­tently. This generally means that replacement motors are re­quired. Early Akai video recorders often had these problems due to lack of heatsinking on the control IC. The best quick confirmation of head performance and align­ment is probably displaying the output from the head amplifier on the CRO, but it doesn’t necessarily indicate precisely where the problem is. Some early Sharp models had a feature built in that would automatically put the deck into the search mode from the play position when a blank part of the tape was reached. It appears that the system monitors the video signal sync pulses and, if these are not present, goes into the search mode. The result is snow on the screen and no sound, until a video signal is encountered, whereupon the systems reverts to the play mode. However, if some defect, such as dirty or damaged heads, prevents the system from sensing a video signal of ade­ quate amplitude, it will assume there is no video, and go into the search mode permanently. What appears on the screen depends on the exact nature and degree of the fault, and may vary from snow to some attempt at a picture but with no sound. And significantly, the makers point out in the instruction manual that the system may not work cor­rectly with poorly recorded tapes. So when I am told that the problem is that the tape goes into fast forward, it is usually due to the machine having dirty heads. Last week, I was faced with just such a situation but one with a sting in its tail. The machine was a model VC-583X, which features this facility. It is owned by an elderly lady customer who complained of exactly the symptoms I would expect from such a problem. A check on the bench confirmed that the lady had described the fault quite accurately; the system was quite Fig.1: the power supply circuitry in the Sharp VC488X, Philips VR6940/75 and Marantz 740A VCRs. Two 1µF electrolytic capacitors labelled C962 and C963 (upper centre) and a 100µF capacitor labelled C970 (lower right) are always prime suspects in this circuit but a mass replacement may save future problems. definitely in the search mode and was producing a grotty speeded up version of the video on the tape, but with no sound. I fixed the problem by simply cleaning the heads. I then gave it a thorough test and made a few other routine service adjustments, such as aligning the audio erase and control heads to track correctly, and cleaning the lower drum assembly to prevent tape stiction, etc. The set bounces Anyway, I was satisfied that it was working correctly in all respects and she took it away. Then, one week later, it bounced. She brought it back complaining, initially, of the same fault. I thought, “Here we go again – a crook tape”, and prepared to clean the heads again. But, as before, she had described the fault very accurately and, ironically, is was this accurate description which alerted me to the fact that it was not the same fault. True, the tape was running fast but, as well as a picture, there was sound. The system was not in the fast search mode at all. Obviously, the problem was more complex than before and she had to leave it with me. The fault turned out to be due to the pinch roller not making firm enough contact with the capstan shaft, resulting in the reel motor pulling the tape through faster than the capstan motor. When I removed the bottom covers and checked the loading motor timing marks I found that indeed they were out. And on removing the mode select switch, I found the gear had cracks, due to age, in the plastic on the axle collar to the switch shaft, and it was slipping. I realigned it with the internal switch mark and glued it in place before reassembling it and setting it all up properly. Once again, it all worked properly, with plenty of pressure on the capstan motor shaft. But when the lady picked it up she neither thanked me or even offered to pay for the considerable additional labour it had taken to repair this second fault ... she just considered I hadn’t fixed it properly the first time! I wasn’t prepared to argue; you win some and you lose some. SC December 1995  57