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With friends like that "With friends like that, who needs enemies?" So goes the popular saying, implying that someone one trusted as a friend has not come up to scratch in a crisis or, worse, has deliberately betrayed that friendship, usually for his own personal gain. Cynical though the expression may be, there seems to be a lot of it going around. These thoughts were prompted by a recent experience involving a customer and a video recorder. He was one of my regular customers and the recorder was a model AV14 manufactured by Mitsubishi and marketed by AWA. This is a relatively recent model which first appeared about three years ago, and one with which I am reasonably familiar. So when the customer opened the conversation with the innocent remark, "Will you have a look at this recorder for me?", I expected some fairly routine electrical or mechanical fault. "Sure", I replied, "What seems to be the problem?" Then he dropped the bombshell: "It's been dropped". That rocked me somewhat. Of all the things one should not do to a video recorder, dropping it would be at the top of the list. Of course there is dropping and dropping how far had it fallen, on what had it landed, and at what angle? These were questions I wanted to ask, if only to help me assess the likely damage and chances of repair. But the sheepish look on the customer's face when he made the announcement suggested that such questions might not be diplomatic, at least at this stage. Picking up the machine, I turned it over and gave it a casual inspection for obvious signs of damage. At first I found nothing, then a closer look revealed a slight flattening of the metal top cover in the rear left hand corner, amounting to only a few millimetres. Well, at least I 46 SILICON CHIP could visualise the angle at which it had landed. And with only that much damage externally, maybe the situation wasn't so bad. But when I looked through the front loading opening it was a different story. The cassette carrier was at a nasty angle relative to the opening, with the left hand side several millimetres higher than it should have been. That set my imagination racing; I could visualise the main frame being twisted or, more likely, fractured, in which case the machine would be a writeoff. I passed these thoughts on to the customer, and suggested that he leave it with me until I had time to open it up and take a more detailed look. And if the damage wasn't as drastic as I feared, I could probably give him some idea of what it would cost to fix. And so we left it at that. A closer look A few days later, when things were a bit slack, I pulled the top cover off the machine and took a closer look. The mechanical deck is well covered by the main printed Special Notice These notes are being contributed by the author who, from 1950 until July of this year, wrote "The Serviceman" in another magazine. We feel sure that regular readers of that series will welcome the opportunity to continue following his electronic adventures in Silicon Chip. circuit board, which would have to be lifted before I could examine the main frame. However, I was agreeably surprised to find that the board itself did not appear to have suffered in any way. I later confirmed that there were no cracks of any kind. Moving the board clear is a somewhat fiddly job in this model. As well as removing the screws holding the board itself it is necessary to remove the front panel and undo a number of screws which hold the operating controls. These are attached to the main board by flexible leads and some care is needed to ensure that these are not damaged as the board is folded back. In fact, this part of the exercise was completed without incident, and I was then able to get a good look at the main frame. Strangely enough, the real problem was not immediately obvious. As far as I could see, the frame was neither bent nor cracked and, possibly due to some kind of optical illusion, it took me a few seconds to work out how it was that the cassette carrier was crooked, even though neither it nor the main frame seemed to be damaged. A frame-up But suddenly all became clear. The main frame was sitting at an angle, relative to the case, and this was why the cassette carrier did not line up with the front opening. And closer examination revealed just why the frame was at this odd angle. The frame is of cast aluminium and is supported in the case by four round pins, or spigots, about 5mm in diameter, which are part of the casting. They are fitted with rubber bushes which, in turn, fit into recesses moulded into the plastic case. And this was where the (Z) UPPER & LOWER DRUM <at> S.GUIDE ROLLER T.U. GUIDE ROLLER<at> AJC HEAD<at> T.U. GUIDE POLE<at> PINCH ROLLER <at> ©TENSION POLE <at>CAPSTAN SHAFT This schematic diagram of a VCR deck layout should help readers envisage the components affected by the unfortunate sequence of events involving the customer's "mate". damage had occurred. The spigot near the front left hand corner of the frame had broken off, together with a small piece of the frame, about half the size of a little finger joint. But that was not all; it had wedged itself under the frame in such a way as to lift the left hand corner of the deck, thus creating the odd angle. Such are the weird things that happen when the irresistable force meets the immovable object. It wasn't much of a job to retrieve the piece of broken casting, whereupon the frame moved back into place and, in spite of the missing support, sat reasonably firm. So normal did everything appear, in fact, that I decided to try loading a cassette. And if it loaded, perhaps it would even play. So I applied power and, when there was no smoke or other signs of distress, pushed a cassette into the carrier. The carrier accepted it and deposited it on deck in the usual way. Well, so far so good and, thus encouraged, I pressed the play button. For a moment I thought this function was going to work also, but I was disappointed. The two guide rollers - (5) and (9) in the accom- panying diagram - which normally pick up the tape and wrap it around the drum, moved only a short distance, then jammed. Finding this fault took a little Ihore time and proved even stranger than what had happened so far. I withdrew the cassette and examined the deck in greater detail. To understand what I found it will be necessary to refer to ·the accompanying diagram and in particular to the tension pole (1) on the extreme left hand side. This pole, as its name implies, is used to tension the tape on the supply side of the drum after the two guide rollers have wrapped it around the drum. It is mounted on a small plate, pivotted on a pin and held in place with a circlip, and which has a short rod extending downwards through the deck. This rod is engaged by a lever which exerts the required tension on the tape via the tension pole. This mechanism sits in close proximity to the curved cut-out in the deck through which the guide rollers, and particularly the supply side guide roller (5) moves during the tape wrapping process. And, by some queer quirk of the forces generated by the fall, the short downward projecting pin on the plate had been forced out of its own opening and into the guide roller slot, effectively jamming the guide roller. And while the fact that this had happened at all was puzzling, the real surprise was yet to come. I couldn't believe that this displacement had taken place without some degree of distortion to some of the parts involved, particularly the tension pole plate. I removed the circlip, pulled the plate out, and examined it carefully. It did not appear to be bent or to have suffered any other form of damage. I replaced it in its correct position, refitted the circlip, then tried the cassette again. And this time it worked; the carrier accepted the cassette, deposited it on the deck and, when I pressed the play button, the two guide rollers picked up the tape, wrapped it around the drum, and set it in motion. I had connected the machine to a TV set and was gratified to see a picture come up on the screen. Granted, there was evidence of tracking error - not surprising NOVEMRER 1987 47 considering what it had been through - but I felt confident that this would respond to routine adjustment. So much for complacency All of which was very encouraging and I felt that I could now regard the machine as repairable and even make a fair estimate as to what it would cost. So much for my complacency. The setup had been running for only a few minutes when the picture suddenly went very snowy, and I had visions of all kinds of nasty faults involving hairline cracks in the main board and the time that might be necessary to track them down. Fortunately, I made a few simple tests first. I stopped the tape, switched the TV set to an off-air channel, and was rewarded with a snowy picture in that mode also. Further investigation showed that the condition could be created or cured by simply wriggling the plug in the "RF OUT" socket on the recorder. Well, that meant a repair job in that section, but I didn't anticipate that it would be all that difficult. So it was time to contact the owner, explain the situation, indicate the likely cost of repair, and see what he wanted to do about it. I rang his home number and the phone was answered by his wife. When I explained who I was and that I was calling about the video recorder the reply was a rather flat and slightly aggressive "Oh that". It didn't need Sherlock Holmes to deduce that there was some lack of domestic agreement in the matter of the video recorder. Naturally, I wasn't keen to become the meat in any sandwich but, on the other hand, I needed someone to make a decision. But before I could say any more, the lady launched into the story about the recorder. "People seem to take my husband for a soft touch. He bought this recorder in a pub for a hundred dollars, from one of his mates". She went on to explain that this mate had been involved in a marital breakup and was short of ready cash. So he had offered my customer "this beaut video recorder for a hundred dollars". Of course, he had conveniently forgotten to mention anything about the recorder's unfortunate encounter with a hard floor, and so the deal was struck, my customer believing that he had acquired a real bargain. It was only when he brought the machine home and tried to use it that he found it wouldn't even accept a cassette. Exactly how he eventually learned what had happened to the machine was not revealed. Perhaps he tackled his mate; perhaps he heard it from somebody else. But one thing is certain: with friends like that, who needs enemies? So much for history So much then for the history. What about the present? I explained to the lady that her husband may not have done so badly after all. I felt sure that the recorder could be repaired, with a possible outlay between $150 and $200, with the latter figure as a firm upper limit. This meant that they would get a recorder for between $250 and $300 a bargain by any standards. As a bonus, there was the fact n{E. \I\DE.O \-\At> 'e.£.E.N INVOLVEO IN ~ W\A~\TA\.. StlE~\<. U~...... . 48 SILICON CHIP that the machine was a current model and, based on my examination of it, one that had had very little use. In that sense it was almost brand new. Apparently I was a better salesman than I realised because, by the time I finished, the lady gave me the go-ahead to fix the machine, without waiting to discuss it with her husband. (Curse my fatal charm). But now I had to deliver the goods. The most important job was to somehow refit the spigot to ensure that the deck would remain stable. Fortunately, the nature of the break made this easier than it might otherwise have been. First, there was the fact that the spigot had not broken off cleanly but had taken a piece of the main frame with it. And second, the angle of the break was such that such stress as it would normally encounter would, if anything, tend to press the two pieces of metal together, rather than the reverse. There was also the fact that, dropping aside, there is not a great --- deal of stress on these spigots; they merely support the weight of the deck. Taking all these factors into account, the repair I envisaged was somewhat unorthodox but, I felt, quite practical. It was based on an epoxy mixture called •'PlastiBond"; a product which, if mixed correctly, cures to a rock hard finish. So I mixed up a batch, coated the two mating surfaces to provide an adhesive function, pressed them together, then built up a thick coating around the joint, taking advantage of as many irregular contours of the frame as possible to provide the best possible grip. The result was a substantial block of epoxy around the joint which should withstand any reasonable stress it is likely to encounter. The next thing to be tackled was the fault involving the "RF OUT" socket. This socket is mounted on a metal box which contains the splitter amplifier and getting at this is quite a job. It is closely linked to the tuner as well as the main board and a lot of leads have to be undone, many needing the solder sucker, before the box can be withdrawn far enough to work on it Then the soldering iron is needed to open the box because the lid is soldered on. I eventually gained access to the inside of the box and the rear of the socket. The pin from the socket protrudes through a hole in a printed circuit board and is soldered to a narrow copper pattern surrounding the hole. The hole is rather larger than the pin, the solder forming a bridge across the gap. This arrangement doesn't impress me very much because even normal plugging and unplugging likely to be encountered in typical use must tend to move the pin slightly, putting a stress on the soldered joint and copper pattern. In this case there had been an abnormal stress on it because the body of the socket was bent several degrees relative to its mounting lugs, and the copper pattern had been pulled away from the board and broken, although making intermittent contact. I removed the socket, straightened it, then refitted it. I ran some solder around the pin in an effort to forming beautifully and had been given "a bit of a flogging". I also gained the impression that any initial reservations on the part of his good lady, concerning his "bargain", had long since been dispelled. So I not only saved a recorder; I might have saved a marriage as well! A fallen General .. suppos~D TO RUN AT l'SV, ~u-r WACS, IN FAC.-f, C LO~E:.~ iO 100V-,,, - ,., fill up the hole in the board and provide mechanical rigidity, then replaced the missing copper pattern with a short length of fine wire. I reasoned that if there was any movement by the pin, the wire should be flexible enough to cope with it. Looking at the damage to the socket etc, I evolved a theory as to how it had come about. I suspect that the lead from the "RF OUT" socket to the TV set was rather short and, when the recorder fell, this lead took most of the weight, even if it wasn't short enough to prevent one corner of the machine hitting the floor. We'll never know for sure, of course, but something had certainly put a lot of stress on that socket. And it had also contributed a lot to the cost of the repair, due to the difficulty of getting at the fault. Only the tracking now remained to be adjusted and this was a fairly routine job. When it was finished, the recorder turned in a first class performance and I had no qualms about have advised the owner to let me go ahead with it. The final bill came out about midway between the figure I had quoted and the owner paid up quite happily. All that was several weeks ago, but the owner was in the shop a few days ago on another matter and confirmed that the recorder is per- My next story is on a quite different theme although some aspects of it are just as puzzling. It concerns a General GC-181 48cm colour TV set, one of several belonging to a local motel and used in the guests' apartments. And the initial description from the owner was simple enough; no picture and no sound. This description was confirmed when I finally switched the set on in the workshop; there was no sound - and neither was there any picture for the very good reason that we had a classic case of frame collapse. Initially, I couldn't decide whether this was likely to be two separate faults, or whether there was a common factor, such as a supply rail, which could be responsible for both. But before trying to track the faµlts on a logical basis I decided to give the set a routine check, dictated by long experience. This set consists of a chassis and main board mounted horizontally in the bottom of the cabinet, plus several auxiliary boards mounted vertically on the main boards by means of plugs and sockets. Among these are the IF Board, Vertical/Power Board, Audio/Horizontal Board etc, plus a Neck Board on the tube. Most of the plugs and sockets are 6-pin types, some boards using two or more such devices to provide the necessary connections. The setup is a very convenient one for servicing, but has not been without problems of its own. The plugs, or male connectors, are mounted on the main board and the sockets on the auxiliary boards, and connections between these are prone to failure. It is the plugs on the main board which are the main offenders. The pins pass through the board and are soldered to the copper pattern on the underside, and it is here that NOVEMBER 1987 49 faulty joints are frequently encountered. As a result, I have long since made it a practice to tackle these joints as a matter of routine whenever I encounter one of these sets, regardless of the fault. And it is surprising how often nothing more is needed to fix the fault. This procedure is further encouraged by the fact that the underside of the main board is fairly easy to get at. Undoing three screws will release the main chassis and allow it to be pulled back far enough in the cabinet to reveal most of the main board underside. And, being a relatively small set, it is easy to tip the cabinet on its side to make it easy to work on. Having done this, and prompted by the frame collapse, I naturally looked first to the two plugs which feed the vertical board. And there it was; around one of the pins (pin 12 of P403) was a tiny patch of what looked like green corrosion. The green lacquer on these boards made it difficult for me to be certain until I checked with a jeweller's loupe, but then there was no doubt. But there was something strange about the condition. For one thing, it appeared to be quite small and confined to this one spot. And even stranger, the corrosion was quite wet. Now I have encountered dry joints, fractured joints, and many kinds of faulty joints, but this is the first time that I have found a wet joint. But there it was, and I can offer no logical explanation for it. I checked carefully for evidence of spillage of any kind around the cabinet or anywhere inside the set, but there was not the slightest sign. So I set to repair the damage. Having cleared away the corrosion I soldered a short length of tinned copper wire to the pin and then soldered this to the copper pattern some little distance away, where it should bypass any long term corrosive effects on the copper track. Then I switched on the set and tried again. Still no sound It came good, at least in that I had a picture. But there was still no sound. So it appeared that there were two separate faults. I pulled 50 SILICON CHIP ., I.I NOW, l HA\IE- ~coo~ t> l)~'( JOl~S I F~C.'t'VREt> jO\~S, ~N~ N\"N'< ~\~\>S Of' l=AU'-'1"< '3'01NTS, &UT nus \S 1\-\E. F\RST ilN\E THAT I H~VE t=OUNO A WET 'J'O\NT,o~)C>)<:;, out the audio/horizontal board, which, as its name implies, carries the audio output stage and horizontal oscillator stage, and reconnected it via extension leads, of which I have several for this set. Then I reached for the voltmeter for a routine check. I didn't get far. The supply rail for the audio stages is supposed to run at 15V but was, in fact, closer to lO0V. Just where this was coming from I had no idea initially, but I didn't like the chances that the three transistors involved - the two output transistors and the driver had survived the situation. It was the physical location of the audio board that gave me the clue. It sits alongside the vertical board which had suffered the faulty plug connection. More importantly, this plug is directly alongside the plug for the audio board, and pin 12 of the latter which carries the 15V supply is alongside pin 12 for the vertical board, which sits at around 106V. What's more, the two copper tracks run side by side for some distance. And that's where the trouble was. What ever the moisture was that had corroded the joint had also apparently penetrated the board and created a path between the two tracks. It is not the first time I have encountered such leakage problems and I have developed a treatment which has proved very effective in the past. The idea is to dig a trough between the two tracks. I use a very small drill, driven by a variable speed power drill, and used as a simple router. It requires a little skill but is not all that difficult if one takes one's time. I took about 15 minutes to do this job but, at the end of that time, all signs of the spurious voltage had vanished. I finished it off with a spray of CRC Clear Urethane Seal Coat, 02049, which is available in an aerosol pack. Then I turned my attention to the audio board and the transistors. As it turned out, only the two output transistors, TR952 and 953, had been damaged and, interestingly enough, one of them had gone open circuit. This was fortunate because, otherwise, the spurious voltage would not have been so immediately apparent. Y'gotta win sometimes! Anyway, that was it. Two new transistors put the sound section back into action and, after a routine check-up, the set was returned to its owner. But I'm still puzzled about the corrosion and what caused it. And why was it so isolated? We'll never know We'll never know I suppose, but here is one other interesting point. My regular readers will recall that several years ago - September 1983 to be exact - I told a story about a set from a motel, a Precedent GC-181 (no relative of the General GC-181), in which severe corrosion was the major problem. In that case, the corrosion was almost certainly caused by the previous proprietor attempting to repair some soldered joints using spirits of salts as a flux. Well, this latest case came from the same motel. Was this another legacy from our heavy-handed plumber-cum-serviceman, but one which had lain dormant for all these years? I agree that the time factor is against this theory, unless the degree of pollution was extremely slight, and it took all these years and perhaps some excessive humidity to provide the final straw. So what do you think? ic