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Toss yer triple or quits! Triple or quits might sound like lengthening the odds a mite unreasonably over the conventional "double or quits" but then the the odds against a fault like this were pretty long anyway. As it happens, it wasn't one of my jobs, and for that I'm duly thankful. No, we are still in that foreign country across Bass Straight where my regular correspondent, J.L., seems to be encountering more weird ones than I am at the moment. And since "weirdos" are what these notes are all about, I'm happy to stand aside and let J.L. take the floor. Here's how he tells it. TV faults come in all shapes and sizes and the first step in solving any problem is to evaluate the symptoms. On this basis, one can then decide in what part of the set the trouble is most likely to lie. Some faults are so simple that only two or three easy tests are enough to identify the faulty component. Others take more time but in most of them the symptoms are a definite lead to the eventual cure. I was nearly going to say that some faults are so obscure that the symptoms are no help at all, but that's not really true. In this story, the symptoms led me on several wild goose chases but in the end there was one symptom that did lead the way. The unit was a Kriesler 660-2iA colour TV set fitted with a 59-3 chassis. It is about 10 years old and is one of those magnificent examples of the cabinet maker's art for which Kriesler was famous. The 660-21A is a double ended console on a solid, fluted plinth. The cabinet is built of 19mm particle board faced with real wood veneer. It weighs a ton but is a fine piece of furniture which the family hopes never to part with. (The owner runs the local fishand-chip shop and he values this set largely because, he claims, it's the only one he knows of that can speak Greek without a Japanese accent! TETIA TV TIP Philips K9 Symptom: Repeated fai lure of line output transistor. True cause of the trouble was not revealed until the normal line output transistor was replaced with an extra high voltage high current type transistor. Cure: C446 (.01 µF 1500V) across line output transistor gone low value. If this cap goes open circuit it can cause puncturing of the picture tube by the generation of excessive EHT. In this case the 62 SILICON CHIP trouble was only a partial breakdown and was eventually exposed by brilliant flashing around the tube base spark gaps and discharges from under the ultor cap. The EHT must have been well over 40kV! TETIA I V Tip is supplied by the Tasmanian branch of The Electronic Technicians' Institute of Australia. Contact Jim Lawler, 16 Adina St, Geilston Bay, Tasmania 7015. Seeing that the set spends most of its time playing Greek videos, or showing Greek programs from SBS, I guess it's just as well it has no such bias!) The owner complained of irregular lines across the screen, or sometimes shaking verticals. The fault was intermittent, sometimes disappearing for hours at a time, but it could usually be relied on to appear at switch on. The way he described it, it sounded like line tearing, a symptom often associated with faulty horizontal drive and just a whisker away from destruction of the horizontal output transistor. Fish & chips I called to look at it on what turned out to be the hottest day of the year. It was 36° outside and inside was not made any more tolerable by the smell of cooking fish and chips from the shop out front. The fault is not easy to describe. The "lines" seemed to be a form of line pairing, where the vertical scan stops working for a millisecond or two, only to catch up again when the fault passes. The shaking looked like very irregular sync, with subsequent lines starting anything from 5µs early to 5µs late. At other times, the vertical lines assumed a regular sinuous wriggle from top to bottom of the screen, like hum bars only faster. There wasn't the slightest uniformity in the symptoms and the fault could have been in any of half a dozen parts of the set. As an indication of how difficult this job was going to be, the shaking stopped after half an hour or so and nothing would induce it to start again. However, one other symptom now appeared. I could see a small, erratic variation in the width of the picture and found that the width control (R691) had no effect. The width is controlled by a BD236 transistor (TR697) and I have found these exhibiting funny faults at times. So I changed it, only to bring back the shakes which masked any change in the function of the width circuitry. I spent an hour looking for dry joints or similar problems but nothing showed up. By this time I'd had enough. The atmosphere was so hot and overpowering that I couldn't think straight and I resolved to get the set back to my workshop where I could work in greater comfort. But the Kriesler is so bulky that I couldn't get it into my small Mazda van. We had to wait until the owner's nephew arrived with his big Chevrolet panelvan. Once set up in my workshop the Kriesler was a lot easier to work on. The first thing I did was to hang my oscilloscope on to the horizontal driver transistor and the horizontal output transformer. Unfortunately, this gave me no joy at all. Both the drive ~nd output were rock steady, during both the shaking phase and varying width phase. The width control was still inoperative so I checked the components around it and its two associated transistors, one of which I had already changed. This proved quite fruitful because both R692 (56k11) and R695 (39k11) had gone high. Also, C696, a lµF 50V electro looked sick. It too was changed but none of this made the width control work. By now I had been all over the width control network with an ohmmeter, my capacitance meter and the oscilloscope. These instruments had told me nothing, so it was back to fundamentals - and a voltmeter is about as fundamental as you can get. Disappearing volts This proved to be the way to go because the emitter of TR697, a BD236, and the collector of TR695, a BC547, were both around 8 volts, instead of the 12 volts specified. The supply rails to both transistors were exactly as specified and, in the absence of faulty components, the trouble had to be in the bias supply, a - 25V rail feeding the width control pot. Sure enough, the rail was reading only about - 1V and the scope showed it to be incredibly spikey . with horizontal frequency pulses. The cause was an open circuit lOOµF 40V bypass capacitor (C810) and replacing this brought the rail back to normal and restored the full operation of the width control. It also restored full operation to the "Straight Outer Vert. Lines" control (R686, 2.2k0) which had had only limited action before the rail voltage was corrected. I now had full control of width and geometry but all of this had done nothing to correct the shaking or pulsing width. Only one thing did show up and I'm not sure of its significance in the context of this story. I happened to touch R785, (a 56011 5W spring type safety resistor in parallel with the horizontal linearity coil) and the picture broke up into crazy diagonal lines. I had serviced this once before when the resistor opened for no apparent reason. Now, touching either end of the resistor with a screwdriver produced the crazy patterns. Suspecting a fault in the resistor, I removed it and cleaned and resoldered the spring. None of this made any difference to the symptoms and the scope showed the waveforms at each end of the resistor to be rock steady. The only possible improvement was that, from this point on, I didn't see the "line pairing" again. The shakes and wriggles continued but the lines across the screen had gone. Next, I went to the small signals board to look at the video signal, in the hope that there might be some irregularity in the sync level that could explain the problem. But I found nothing. The sync separator is in one of two chips on the horizontal control board. I replaced both chips and went very carefully over the board, looking for dry joints, dodgy electros, or anything else that might play up with the horizontal drive. I even removed and checked the AUGUST 1989 63 been able to measure anything, or observe anything on the scope, that was in any way out of place. For the time being, I ignored the shaking and wriggling and concentrated on the size variation. This had to involve a source which affected the horizontal and vertical circuits equally. There were only two such possible sources: the power supply and the picture tube. I had already eliminated the power supply. Its output was rocksteady without the slightest trace of ripple. So if it wasn't the power supply, it had to be associated with the picture tube. There is only one picture tube mechanism that I know of that allows the size of the picture to change; the EHT voltage. It will bloom if the EHT drops and shrink if the EHT is too high. A tiny picture results if the capacitor across the horizontal output transistor fails and allows the EHT to go sky-high. This is fairly common in some Philips sets and often results in the destruction of the picture tube. My problem was how to look at the EHT with the tools I had on hand. I had already found that the input to the horizontal output transformer was rock steady, indicating that the trouble could be either in the transformer itself or in the tripler. The ideal place to look for trouble in this area would have been the input to the tripler. An unsteady BkV would have placed suspicion on the transformer or perhaps the tripler. But BkV at 15kHz is not easy to observe with any degree of accuracy. I then turned to the next most accessible measuring point. This is the focus voltage output and is only one high-voltage diode away from the BkV input. But when I used a· high voltage probe to measure the focus voltage, I realised that it wasn't going to be so easy. Trying to see small variations around an BkV reading on a 30kV full scale meter was asking a bit much of both the meter and my tired old eyes. The breakthrough All in a flash Then I saw something that I should have noticed hours earlier. Not only was the width varying slightly but so also was the height. This opened up a whole new range of possibilities. Just then I had a flash of inspiration - I didn't have to read the full BkV focus supply. Because the BkV is applied to a resistive divider chain, this would give me several lower voltages, each of which SERVICEMAN'S LOG -CTD D759 8Y206 '-~ ~ 13Y206 To SK704 Pin 3 --l C751 •01 C807 3900 ~~~ To SK704 Pin 6 689 82~ t6S7 :684 R823 / R825 30V ~:::* Fig.1: the relevant circuitry of the Kriesler 59-3 TV receiver. The width control, R691, is at bottom centre, while the focus control network, R760, R761, R762 and R763, is at the top, above the tripler. horizontal driver transformer and replaced the horizontal drive transistor, but there was still no improvement. By . this time I was getting desperate. Something was causing the picture to break up and something was making the width vary. I had no idea whether this was two faults or two manifestations of the same fault. I hadn't 64 SILICON CHIP would be an exact percentage of the full focus voltage. In greater detail, there is an 8.2MO resistor (R760) from the BkV line to the focus pot (R761, 2.7MO), then two 5.lMO resistors, R762 and 763, in series to chassis. The junction of the two latter resistors is at about 2kV and this is within the range of my oscilloscope. In no time at all I had a trace on the screen showing part of the focus voltage popping about between 1.9 and 2kV. And, by implication, the EHT was also jumping about, probably between 25kV and 26kV. Of course, this still didn't tell me whether it was the transformer or the tripler that was faulty but, as the tripler was the easiest part to substitute, it was my first choice. It took only five minutes to fit a new tripler and at the first switch on I had a rock-steady picture. Although this was the best result I'd had since starting the job, I wasn't prepared to accept it as finished because, at this point, I had only cured the shrinking pro. blem. The shaking and wriggling were not necessarily explained by a faulty tripler and might well have indicated another fault waiting to show up later. I put the set through a dozen onoff cycles and let it run for several hours but there was no sign of any more trouble. Then, to make sure, I replaced the original tripler. This removed all doubt because the shaking, wriggling, shrinking picture was back with all its annoying features. So it was the tripler after all, even if this didn't explain all the symptoms. Over the years I have replaced hundreds of faulty triplers and almost invariably these have been for internal short circuits. A very few have gone open circuit and some have burst irreparably from their plastic cases. I've even heard of, but never seen, a tripler that was intermittent go and no-go. But I've never seen one that was sort of intermittent but not quite! The first story started while I was briefly absent from the shop, having left it in charge of my secretary who comes in from time to time to help straighten out my paper work. She took a phone call from a potential customer, requesting that I come to their home and look at their TV set. Acting on my instructions she advised the caller that it would be better if he could bring the set in (I'm trying to cut down on house calls to save costs). The caller agreed and, a couple of hours later, a car pulled up outside the shop, with a man and a woman in it and a TV set on the back seat. As I walked out to the car I could see what appeared to be the moulded back sitting on top of the cabinet. In answer to my unasked question, the lady explained that they had had some difficulty in getting the set into the car, so they had removed the back to make it easier. Then she added, "We got it in OK, but there was a funny hissing noise as we settled it on the seat". Well, no prizes for guessing. As I moved in for a closer look I noticed another strange aspect. The cabinet, basically of chipboard, had no veneer of other covering of any kind; it was simply bare chipboard! I also identified the set and realised that it was quite long in the tooth. It was a 54cm Mitsubishi and would have been between 12 and 13 years old. It was one of the early sets on the market after the introduction of colour. But all this was rather academic. Tipping the cabinet forward on the seat I showed the couple where the neck of the tube had been broken; it was just in front of the neckboard, the base section and the neckboard having come away as a unit. That was when I pointed the way to the tip. Well, not in so many brutal words but, as I pointed out to them, there was little point in trying to salvage the situation. Supplying and fitting a new tube - with no glass allowance - would cost at least $300, and perhaps as much as That way to the tip as $350, depending on the current After that story the best I can tube price. And that was without considercome up with is rather puny by · comparison but it does highlight ing the original fault which started the whole sequence. I had to warn some customer problems. FIX-A-KIT Kit Repairs - $1 5 per hour. Normal Rate - $35 per hour. No charge for kits that can't be repaired . 3 month Warranty on repairs. Construction - fixed or hourly 1 2 Month Warranty on Manufactured Kits. Custom Designing, Manufacturing, Large or Small Quantitites. HYCAL INSTRUMENTS Design, Manufacture, Repair of Electronic Equipment. (02) 633 5897 Unit 4, 62 Great Western Highway, Parramatta, NSW 2150. Trading hours: 8am to 3pm Monday to Friday. D.DAUNER ELECTRONIC COMPONENTS WE STOCK A WIDE RANGE OF ELECTRONIC PARTS for • Development • Repair • Radio Amateur • Industrial Electronic • Analog and Digital WHILE STOCKS LAST * THE FAMOUS TR-DIP METER (as featured May '89) $98.00 * CAO-VALVE 3ACP2A $45 .00 * PHILIPS IA-IMAGE CONVERTEH VALVE XX1080 $45.00 (For use in infrared sight experiment systems) Come and see. Showroom: 51 Georges Crescent, Georges Hall, NSW 2198 (Behl■d Calte1 Service Station In Blrdwood Road) Phone 724 6982 TRADING HOURS: Monday to Friday 9.00 a.m. to 4.00 p.m. Saturday from 9.00 a.m. to 12.00 noon. AUGUST 1989 65 SERVICEMAN'S LOG -CTD them that it could add another $100, or even more, to the overall cost. Fortunately, they seemed to accept the news philosophically. The lady simply shrugged her shoulders and said, "Its rather bad news, isn't it". And that about summed it up. But one final point. If a TV set has to be carried on the back seat of a car, it should always be loaded with the tube face towards the back of the seat; the weight distribution is far better that way. And, of course, a set should never be transported with the rear cover removed. Leaky cat And while on the subject of 66 SILICON CHIP unhappy endings, here's one about a video recorder. It was a Sharp Model 9300, about five years old, and was left at the shop while I was absent. There was little information with it; just a rather cryptic message, "It doesn't go - fix it". Knowing the owner, who is a rather aggressive type, this message didn't surprise me. When I switched it on its static behaviour was rather erratic and I hesitated to load a tape into it, lest a mechanical fault should chew up a good tape. Instead I undid the four screws and removed the top cover to reveal the copper side of the main board. And that was as far as I needed to go. Near the rear centre of the board was a patch of corrosion about 70mm in diameter and, to the left of this, a smaller patch aboout the size of a 20c piece. Something had obviously been spilt on top of the machine. Exactly what was a puzzle. It is not unusual for drinks to be spilt on VCRs - anything from coffee to beer - and, while they all make a mess, they seldom cause corrosion. I moved in for a closer look and made what modern jargon writers would probably refer to as "olfactory contact" - I could smell it. It was strong, pungent, and unmistakable - feline urine! I backed off quick smart but not before I'd seen enough of the damage to know that it was beyond repair. A whole group of tracks had been eaten through and I could only speculate as to what effect the contamination had had on the insulating properties of the base material. As to what other damage had been caused, that was anyone's guess. I rang the owner and gave him the bad news. He didn't take it too well and obviously wasn't prepared to take my word for it. So I suggested he come to the shop and see for himself which he did, but even then he refused to accept the situation; as far as he was concerned it was simply a matter of patching up a few tracks. I pointed out that there were more than a "few" tracks, that they were very close together, and that repairing them would be a big job. I put a tentative price of $100 on the job and that was not taking into account any other faults which might show up when the tracks were repaired, such as the central microprocessor IC. This would cost around $70, plus the cost of fitting. And there was no guarantee that the repair would be long lasting. Finally, he went through the motions of accepting my advice but he went off muttering something to the effect that he didn't believe the cat was to blame. Well, that's something between him and the puddy tat. Why do some cats do this? This is not the first such incident I have encountered, though it was one of the worst. I assume that it is the gentle warmth that attracts the moggie in the first place; beyond that the reader's imagination can probably fill in the gaps. ~