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SERVICEMAN'S LOG The view was fabulous, but ... Yes, there’s usually a “but”, involving some kind of a trade-off for what looks like a perfect situation. In this case, a location with a fabulous view exacted its own price in terms of appliance reliability. It really was a beautiful view. This lady customer lives right on a beach front and one would have thought that, with paradise right on her doorstep, she would hardly need a TV set. In fact, she owned a very large double-ended lowboy with an AWA-Mitsubishi SC6341 AS630 chassis. It was the size of the set that necessitated the house call. And I was going to have to fix it in situ, because I could­n’t move it unaided. The problem was loss of vertical scan, there being just a horizontal line across the screen. I should have realised from the state of the cabinet veneer that the environment may have been to blame. When I removed the back, the cause was obvious – salt air corrosion. All the tinplate areas were rusty and the aluminium was pitted. Also, the horizontal output transformer didn’t look long for this world, with a telltale carbon track on the plas­tic. But worse still was the state of a lot of the small com­ponents, many of which were green from copper oxide Fig.1: the relevant section from the AWA-Mitsubishi SC6341 colour TV set. The vertical oscillator section of IC201 is shown at top and this drives the vertical output transistors (Q451 and Q452) at the bottom. The height control, VR452, is to the left of Q452. 40  Silicon Chip corrosion. Altogether, the long-term reliability of the set looked very poor and I informed the lady of this prognosis. She asked me to see what I could do. This chassis is the stereo version of the ML series and most of the deflection circuits are the same. The vertical time­base is fairly simple in terms of component numbers – a 48-pin IC (IC201) carries the vertical oscillator and drives the two output transistors (Q451/Q452). The correct value of 11.4V was applied to pin 33 of the IC but the collector of Q451 had 113V on it, in­stead of around 65V, suggesting the transistors were switched off and not being driven. Sometimes these circuits can be difficult to service, as it is often a chicken and egg situation, where a fault in any sec­ t ion, including the feedback path, can stop it from working. In this situation, it is hard to know where to start, especially as I didn’t have the CRO to turn to. But as luck would have it, the problem was fairly obvious from the state of the height control (VR452) which was badly corroded. I tried to adjust it while watching the screen. Impossible – the cabinet was too large; I had to ask the lady for some help. She was able to tell me that the horizontal line had expanded and was trying to fill the screen as I adjusted the control; that is, until the control disintegrated. I replaced it and the picture was restored. I then refitted the back and was going through a final check when I noticed that the stereo lights were not on and the sound was in mono. This was all I needed to remove the back again. This set uses the TDA3800G decoder and that was my initial suspect. However, I had blamed this unit unfairly on a previous occasion, so I looked around for another possible cause. The preset pots VR301, VR302 and VR303 caught my eye; they all looked bad. But replacing them presented a problem because I didn’t have any alignment equipment with me. I took a punt and used an in­delible felt tip marker to mark the positions of the wiper arms and then replaced all three controls. Fortunately, only VR302 and VR303 were the culprits and, by setting the wipers at the same angle as the originals, full stereo sound was restored and the LEDs were alight. I finally emptied half a can of CRC 2-26 all over the corroded areas and the horizontal output transformer, then I wiped and cleaned off the excess and dirt with a cloth. After replacing the back I had a word with the lady on how best to protect the set, at least for a while. I suggested she move it away from the open window overlooking the sea and place it as far as possible on the other side of the room, or even in another room on the other side of the house. Also, I recommended that she cover the set with a sheet, blan­ket, or even a plastic tarp when she wasn’t watching it, espe­cially during any humid weather or when onshore winds prevailed. She compromised by covering it with a table cloth away from the window and as far as I know it is still working, six months later. But, as I said earlier, there was a price to pay for that fabulous view. The red face My next story involves a video recorder that bounced. Any­thing that bounces has the makings of a red face situation and this was no exception. But there is a twist to the story. It started when a new lady customer brought a Philips VR6448/75 video recorder into the shop and complained that it chewed the tape on ejecting – sometimes. She added that she used the machine a lot and would appreciate it if I could fix it as soon as possible. It so happened I wasn’t particularly busy that day, so I tackled it almost immediately. The intermittent aspect didn’t help. It took about 10 tries to create the fault, whereupon it became fairly obvious; the tape wasn’t being fully wound back into the cassette prior to unloading, leaving a length of tape outside to be chewed up by the ejecting action. This turned out to be a partial failure of the reel idler assembly. I removed this, cleaned and tested it, replaced it, and tested it again. I then checked the idler shaft and found it to be sticking. It didn’t respond to normal treatment and so I decided to fit a new idler assembly and a set of belts and tyres. This machine is made by Sharp and so I rang the lady and quoted her on the basis of Sharp replacement parts. This worked out at $135.00 – $52.50 for the parts and $82.50 for labour. She accepted quite happily and I told her it would be ready that afternoon. I fitted everything back in, cleaned the heads and the machine generally, tested it, and was quite confident that it was in perfect condi­tion. The lady collected the machine later October 1995  41 in the day, paid by cheque, and thank­ ed me for being so prompt; another satis­fied customer, or so I thought. A real blast About three weeks later, I answered the phone one morning and a bloke identified himself as being from one of the local TV stations. And without waiting for any acknowledgement, he let fly with “what sort of guarantee do you give?”. Then, again without waiting for an answer, he went into a long diatribe about how I had ripped him off and that I didn’t know what I was doing. What’s more, he demanded that I should immediately call at his place and fix his recorder properly. And he added that the tech­nicians at his station could have fixed the recorder properly at half the outrageous price I had charged (I wondered why he hadn’t used them). I’m afraid the strength of his blast caught me off guard and, initially, I couldn’t get a word in edgeways to even identi­fy the recorder. I did eventually and, of course, it was the lady’s husband, But even then, it was an effort to find out what the problem was. All he would say was, “It’s doing the same thing – it won’t eject” (which wasn’t the same thing). When he finally paused for breath I told him that my war­ranty was 90 days for the parts I had used and for my work; nothing else. I invited him to bring the recorder back in and I would look at it immediately. That wasn’t good enough – I had to drive out and fix it. I baulked at that and repeated my offer to check the ma­chine but only in my workshop. “Right”, he said, “I’m going to go through you like a packet of salts”. And he hung up. The “packet of salts” took the form of a call, shortly afterwards, from Consumer Affairs, acting on a complaint from him that I wasn’t prepared to fix his recorder. The C.A. man was strictly neutral and listened politely while I gave my side of the story and explained that I would attend to the matter as soon as the recorder was brought back. He said he would relay that to the complainant. Another week went by, a somewhat worrying period. No-one likes a repair to bounce, for whatever reason. While I was sure I had done a thorough job, there is always the risk of something being overlooked. But, try as I might, I couldn’t think what. Then he appeared, carrying the recorder. He was a lot quieter now – doubtless on the advice of the C.A. man – and was even polite, in a very reserved manner. I tried to be equally polite. He offered to leave the recorder with me and call back later. But I insisted that he wait while I examined the machine in front of him, to which he reluctantly agreed. I plugged the recorder in and confirmed the nature of the fault; a cassette was stuck inside and wouldn’t eject. I could hear the motors trying to turn but without result. It was clearly not the original fault. I removed the covers while he watched and began to turn the eject shaft gently by hand. And as the cassette lifted clear of the deck floor I experienced a wave of relief as I saw the cause of the problem. And it was simple enough for even the customer to see and understand – a ballpoint pen jammed underneath it. Talk about a red face – his reserve collapsed totally. To give him his due, he did apologise and said he would contact Consumer Affairs and put that right. But he didn’t offer to pay for having it fixed again. I had to realign the ejector assembly with the loading motor mode select switch, to restore the correct sequence. And I tested it to his satisfaction while he waited. Technically, I could have charged him again. But I wasn’t going to push it – honour was satisfied. J. L.’s video camera And now, on a completely different theme, I have a quite unusual story from my southern colleague, J. L. of 42  Silicon Chip Tasmania. Here’s how he tells it. I’ve had a very interesting job over the last few days. It was the sort of job that usually goes only to specialist techni­cians, so I’ll tell it here as a word of warning to others who might get involved and as a gesture of thanks to the highly skilled technicians who helped me out of my trouble. It concerned my own video camera, a Panasonic model NV-MS4A. It’s a full-size Super VHS camera, a big, heavy thing that produces superb pictures. Or at least, it did until my son gave it a hefty thump while out filming one day. As far as he can recall the camera was in its fitted case when the thump occurred and there is no sign of damage on either the case or the camera. But in fact, the camera had suffered internally and would not work next time he tried to shoot. The deck would not load or unload a tape but had stopped half way through one or the other process. However, it did eject the tape and a mangled S-VHS cassette was the result. Next day, I took it to the local Panasonic specialists for repair. I was over optimistic because, as it turned out, they had three weeks work on hand and could not help me for at least that long. And I needed it before that. “Why not do it yourself?” they asked. “You’ve done plenty of VCRs and this is only a more com­pact version of the same thing!” Well, I had a manual for the camera and they offered to make available some vacant bench space and promised moral sup­port, so I set to work. First, I removed all the screws as per the manual. There were about 17 of them altogether and I expected the camera covers to more or less fall off. Alas for my high hopes! I pulled and tugged and pushed and prodded for 20 minutes but couldn’t get the thing apart. I worked so hard that I feared I might break the plastic panels but nothing I could do would expose the inside of the camera. Then their senior camera technician came over and said, “Here! What are you doing? You’ll smash the thing, handling it like that!” And with that, he poked a small screwdriver in through a couple of holes in the cover and both sides simply fell off! It seems that Panasonic designed this camera to a “belts and braces” standard. Not only are the covers held on with lots of screws, they are also held in place with plastic clips moulded into the inside of each half shell. Provision is made for pushing the clips out of the way to release the shells but no mention is made of this in the manual. You have to find out for yourself, or be shown, where these clips are before you can open the camera. One could smash the thing to pieces trying to get it open but once the secret is known, disassembly is quick and almost painless. Now that the mechanism was exposed, it was easy to see what had happened. A pin on a lever, intended to ride in a groove on the master cam, had jumped out and was sitting jammed on the top surface of the cam. It was easy enough to slip the pin back into the groove but this left the mode switch and mechanical timing way out of place. I struggled with gears and levers, trying to get everything back into position but I was getting nowhere. The mechanical instructions in the manual I was working from were written in excruciating Japanese English, so I had to ask for help from one of the other technicians. He is a better interpreter than I (or else, he has been through all this before) and he soon had every­thing back into place and the mechanism working properly. I reassembled the camera, refitted the covers and tested the unit to my satisfaction. It was the first time I had ever been inside a camcorder and I came away thinking that it was not a place in which I would like to spend too much time. Apart from anything else, my fingers are too thick and too insensitive to handle the tiny parts. K ALEX The UV People ETCH TANKS ● Bubble Etch ● Circulating LIGHT BOXES ● Portuvee 4 ● Portuvee 6 ● Dual Level TRIMMER ● Ideal PCB DRILL ● Toyo HiSpeed MATERIALS ● PC Board: Riston, Dynachem ● 3M Label/Panel Stock ● Dynamark: Metal, Plastic ✸ AUSTRALIA’S NO.1 STOCKIST ✸ K ALEX 40 Wallis Ave, East Ivanhoe 3079. Phone (03) 9497 3422, Fax (03) 9499 2381 TRANSFORMERS • TOROIDAL • CONVENTIONAL • POWER • OUTPUT • CURRENT • INVERTER • PLUGPACKS • CHOKES It’s not fixed yet Now, if you think that this is the end of the story, you’re wrong. It’s only just begun. I used the camera that weekend and shot some perfect foot­age. Then my son took the camera on the Monday and that evening complained that it would not record in colour and had a red line down the righthand side of the picture. He felt it might be a physical problem since the camera seemed to work reasonably well when hand-held but played up when mounted on the tripod. We soon found that we could make the fault come and go by pressing STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1990 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 October 1995  43 that suggested to him that this was a delay line fault. As it turned out, he wasn’t wrong. I had quite a difficult job finding the delay line. In fact, there are two in the camera, one a 1H line and the other a 2H. Neither looks anything like a conventional TV delay line. The 1H line is in an 8-pin IC package, similar to but smaller than a 555 timer chip. The 2H delay line looks like another IC but is in a 16-pin package. Once I had identified the delay lines, I was able to exam­ine them for signs of dry joints. This was rather inconclusive since, under a strong glass, the solder looked rather crystalline but no more so than hundreds of other joints on the board. Still, I had been assured that at least one of the 24 pins on these two chips had to be loose, so I fitted the finest point into my soldering iron and gave each one a touch of heat. And that was all it took. The fault disappeared and has not returned. I haven’t been able to learn if my friend solved the prob­lem using experience or theory. Chroma delay line problems are so rare that I have never had one in all my years of servicing colour TV sets or video recorders. They are not unknown, of course, but are so unusual that few people build up a fund of experience. lightly on the side of the camera body, in the vicinity of the main PCB. It was as well that I’d learned the secret of the plastic clips because I was going to have the covers on and off many times over the next few days. With the main PCB exposed, I found that the fault did indeed respond to gentle pressure but only on one end of the board. It was obviously a dry joint but on a 100 x 150mm double sided board, thickly coated with micro-miniature surface mount components, I didn’t like my chances of finding it. The fact that the fault seemed only to affect the chroma circuits helped to reduce the area of confusion but, even so, it involved hundreds of tiny components on both sides of the board. I used a fine dental pick to gently prod and poke all the components I could identify as part of the chroma circuitry. The PC patterns are given in the manual but only the larger and less crowded components are listed. Dozens of chip resistors and capacitors are simply not shown on the pattern, 44  Silicon Chip which makes iden­tifying the various parts rather difficult. Several times I poked at a component and the fault disap­peared. Whenever it stayed “disappeared”, I hoped that I might have cured the problem by accident and so reassembled the camera and gave it a test run. This went on half a dozen times before I realised that, by myself, I would never be able to solve the problem. In the absence of more precise information about the exact nature of the fault and therefore its physical location, I could hunt forever and never track it down. So it was back to my friends at the service centre. I played back some of the test tape I had been running and their senior technician said straight away “that’s a delay line fault!” When I demonstrated that it could be turned on and off by pressing on the board, he opined that it had to be a dry joint on one or another of the delay line pins. It seems that it was the red line down the righthand side of the screen Minor hassles The job wasn’t quite over since I had no end of trouble getting everything back into place. I misaligned a 30-pin plug and socket connector and had the whole machine reassembled before I found that the camera section wasn’t working. Then, when I fixed that, there was no servo control because a 30-pin flexible connector had slipped out of place. Then the zoom lens wouldn’t work, because I had somehow dislodged its tiny 3-pin plug in the process of replacing the side cover! It’s been an interesting experience but I have never been so pleased to complete a job. I would never have undertaken the task if the camera had not been wanted urgently. I think my friends at the service centre are entitled to every penny they make from camera repairs. Thanks, J. L., for a most interesting and unusual story. It just goes to show that you never know what you can do SC until you try.