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SERVICEMAN'S LOG Whingeing Willie & the bouncing TV What does one do when a set bounces? Much depends on why it has bounced but there is also the customer’s reaction to consider. Most customers are understanding & reasonable – even apologetic. But every so often ... Yes, every so often one strikes a stinker and this is about one such customer. But first, why do sets bounce? Broadly, there are two categories. The one we all dread is the one which, strictly speaking, is our own fault. The scenario is typical: an intermittent fault with erratic behaviour, resulting in a long and involved process of trial and error to track it down. Usually, this involves re-making suspect joints, running the set through hot and cold cycles, and replacing the most likely components, based on previous experience, measurements and a certain amount of gut feeling. Nothing works at first but, eventually, one particular effort seems to be the answer; the set runs for days, or even weeks, without so much as a hint of trouble. So back it goes to the customer. A week later – or even sooner – it is back in the shop, with the customer complaining that it is just as bad as ever. The customer’s approach will vary. If they have been warned as to such a possibility – and I make it a point to do this – they will usually accept the situation philosophically, or even apologeti­cally. A few will be more upset, but mostly at the device rather than the serviceman. In any case, one can only start over again, and write off the extra time to experience – the only good point being that many suspect components have already been eliminated. And, with persistence, the real culprit will eventually be found. The other bounce The other kind of bounce is quite different and typically involves a dead set with a routine fault that’s easily recog­ nised. The faulty component is replaced, any minor adjustments attended to, and the set goes back to the customer – another job completed. Except that, a week later or so, it’s back in the workshop – dead again. It’s a completely different fault, of course, and it is not the serviceman’s fault, but one can hardly blame the customer for not always appreciating this point. But again, most customers will accept a truthful explana­tion, if it is carefully presented. And I normally waive any further labour charge in the interest of goodwill. But, as I said at the beginning, once in a while one strikes a stinker. 56  Silicon Chip This story started with a phone call from a stranger. He opened the conversation by asking whether I provided warranty service for Samsung sets. I said “yes” and asked what was the nature of the problem. It was quite simple as he described it; the picture had crept down from the top and up from the bottom ever so slightly, revealing “...a little black line”. So I said, “OK, bring it in and we’ll have a look at it”. And so it duly turned up at the shop, along with the various sales dockets which I had asked him to bring along, to substan­ tiate the warranty claim. The set turned out to be a model CB-3325J, fitted with a P/58SC chassis. I turned it on while he was there and, yes, his description was quite accurate; a very mar­ginal degree of vertical underscan. I told him it looked as though it needed nothing more than a small adjustment and suggested that he leave it with me for an hour or so. I would have to remove the back of the set and I wanted time to confirm that the fault was a simple as it looked. As it transpired, he had other things to do, so he suggested that he leave it with me and call back in a couple of days. Well, that was fine by me; it would mean that I could fit it in with other jobs more conveniently and also allow me to soak test it for a couple of days. So everyone was happy. I also took advantage of the extra time to run the set for several hours before I touched it. And it simply performed as it had when first switch­ed on; there was no change of any kind. Subsequently, I pulled the back off, reset the height con­trol and looked for anything else that was obviously wrong, but found nothing. I then replaced the back and ran the set daily until the customer returned. It ran perfectly during all that time. When he returned, I filled out the necessary warranty claim, demonstrated the set to him, and sent him on his way. And, as usual, one tends to mentally write off such jobs almost imme­diately; there are other jobs to do. The balloon goes up But a couple of weeks later the balloon went up. The cus­tomer was on the phone in a most belligerent manner. His com­plaint now was that the picture had shrunk drastically; it was now only about 10cm high in the centre of the screen. But more to the point, he was accusing me of not having fixed the set in the first place. I pointed out that there was no “fixing” involved in the first call; it was a simple adjustment. His reply was that I should have seen that this was going to happen, to which I testi­ly replied that my crystal ball had been a mite cloudy that day. At a more practical level, I advised him to bring the set back in. It was still under warranty and it would cost him nothing to have it fixed. And so the set landed back on the bench and the owner went on his way muttering all kinds of nasty things about Samsung, yours truly, and the industry in general. I let him rave; I had the more important job ahead of finding the fault. I wasn’t expecting it to be a particularly difficult job but, as I have mentioned in these notes before, Samsung circuits and manuals are disturbingly short on voltages and waveforms. In some cases, the only voltages given are the rail voltages and this is something which can cause a lot of wasted time. One important point I noted about the fault was that there was no suggestion of non-linearity; it was a simple loss of amplitude only. Such a clue could be valuable in nominating the most likely fault areas, or in interpreting CRO patterns. I began by making a preliminary check around IC301 (KA2131), a 9-pin vertical output IC – see Fig.1. My first check was at pin 4, the supply rail pin. This connects to the 25V rail via diode D302 and it checked OK. From here, I went to the height control, VR301 (1kΩ) and simply tried varying it. I wasn’t really surprised when it had only a marginal effect. Jungle chip My next stop was IC101, a 28-pin jungle chip which, among other things, contains the vertical oscillator, horizontal oscil­lator and the sync separator. I spent some time here with the CRO, particularly around pins 3 and 4. Pin 3 carries the vertical drive signals for IC301, entering that IC on pin 6. Pin 4 takes feedback signals from the output circuitry of IC301. Well, there were waveforms at all these points and most of them seemed to have reasonable shape but, without any reference, I was flying blind in regard to amplitude. However, I was some­what suspicious of the oscillator amplitude (or vertical drive voltage) on pin 3. It did seem a bit light on. This thought lead me to pin 2, which is the supply rail for what is labelled the “Ramp Gen” but is really the vertical oscil­lator. This pin is connected to the 12V rail via a 470kΩ ¼W resistor (R302). And this was the culprit; it had gone high. December 1993  57 SERVICEMAN'S LOG – CTD Fig.1: this diagram shows the jungle IC (IC101) & the vertical output IC (IC301 at top right) in the Samsung CB-3325J colour TV set. It was routine from there on. I fitted a new resistor, reset the height control, checked everything over once again, and gave it a soak test for several days. I also took the opportunity to make a complete voltage check around these two ICs, and other important points, and filed them with the manual. I then called the customer and told him it was ready. He called in the next day, signed the warranty claim, and went on his way grumbling and mumbling, mainly along the lines that the set was “no so-and-so good” etc, etc. I didn’t bite; I was only too happy to see the back of him and I hoped that it would be for good. Alas, it was not to be. Would you believe that he was back on the phone again barely a week later? His complaint was legiti­mate enough – the set was now completely dead. Privately, I wondered what I had done to deserve such bad luck. Of all the customers they could have picked, the gods had to pick Whingeing Willie. OK, so he did have a gripe. But what really annoyed me was that he was now quite abusive at a personal level – as if the failure was my fault. And customer or not, I made this point quite strongly. The failure was not my fault; odd components can fail at any time and it was just unfortunate that there had been two such failures in 58  Silicon Chip quick succession. Such a coincidence was rare but it was not the first time it had happened. And I went on to state the situation as I had before; the set was still under warranty, he could bring it in at any time, I would give it priority, and it would cost him nothing. So he duly turned up with the set and continued his tirade of abuse. But I wasn’t prepared to take it lying down and took the opportunity to have my say. I repeated the point that the failure was not my fault, emphasising that it is virtually impossible to predict when a particular component is going to fail. Fig.2: the horizontal output stage in the Samsung CB-3325J. It failed when IC101 shut-down due to some other fault. On a percentage basis, component failure rates are remark­ably low – and have improved amazingly in recent years – but the day of zero failure is a still long way off. That is one of the reasons why manufacturers provide war­ ranty cover. And in this case the warranty service had been close at hand, he had not had to resort to a commercial carrier, and the job had been done in the shortest possible time. In view of this, I told him that he didn’t really have much to complain about. I doubt that I really convinced him but it quietened him down somewhat. Anyway, he went off, still in something of a high dudgeon but with a silencer now fitted. And so I turned to the more practical problem of finding this new fault. It wasn’t very hard really, although there was a side effect. It soon became apparent that IC101 was again in­volved, since it now appeared to be completely inoperative. This lead me to the supply pin (pin 7) which is supposed to be at +12V. Only there wasn’t any voltage on it. The culprit was resis­ tor R121, a 1.5Ω resistor, apparently part of a decoupling net­ work. It was open circuit. A new resistor soon had the set up and running again but it was still not quite right. It was now suffering from significant horizontal underscan. I was glad I had caught that before Whinging Willie had had a chance to see it; he’d have had a seizure on the spot. Again, it didn’t take long to find the culprit. It was another resistor, this time R411 (68Ω). This resistor supplies current from the 16V rail to the collector of the horizontal driver transistor (Q401) via the primary of the horizontal drive transformer (T401) –see Fig.2. It had gone high by just enough to affect the drive. But it wasn’t really the resistor’s fault. Deprived of drive from IC101, Q401 would have been drawing excessive current and R411 would have been well on the way to complete failure. Anyway, it was easily fixed. I went over the set again, made sure all adjustments were optimised, tried to visualise what else might go wrong, and finally pronounced the job finished. I made out the warranty claim and rang the customer. He wasn’t any happier when he called this time. He con­ tinued his abuse of both Samsung in general and myself in partic­ ular. Among other things, he declared his temptation to “...go and wrap the set around Mr Samsung’s ears”. I told him I didn’t think that would do him any good and I think this made him realise just how ridiculous the suggestion was. And I had the last word – I reminded him again that he had been given first class service, with no argument, at no cost, and a minimum of waiting time. What more did he expect? At that he went on his way and that, thankfully, was the last I saw of him. It all happened many months ago and I am hopeful that this happy state will continue. I don’t want his custom again. Customer ignorance But the incident did make me think. Although this was an extreme case, customer dissatisfaction along these lines is nothing new; it has been cropping up from time to time for as long as I can remember. So why does it happen? Basically, it is due to customer ignorance, although the industry itself may be at least partly responsible. More exactly, this ignorance is in the form of two funda­mental misconceptions. The first is that the serviceman, by some magical process, is able to test – or even look at – any compon­ent and predict it’s end-of-life point. The second misconception arises December 1993  59 out of the first. It as­sumes that because such predictions are possible, a competent serviceman will check all components in the device being serviced and replace all those which are about to “wear out”. And this “wear” concept is another part of the misconception; the idea that all parts will eventually wear out. I won’t dwell on the impracticality of testing every component in a set; suffice it to say that the mind boggles! So the message we have to try to put across is that very few modern components have a predictable life. Valves did and picture tubes still do but most others have a theoretically infinite life. When they fail, it is usually a catastrophic failure which can happen at any time. And, of course, it is quite impractical to test all the components in a set. Does the customer have any idea how many there are? In most cases, the part would have to be removed for testing and then replaced. Quite apart from anything else, this could easily create more faults than it would prevent and it would really amount to a virtual rebuilding of the set. Would the customer be prepared 60  Silicon Chip to pay for such an exercise? Of course not. Having written all that, I am forced to concede how seem­ingly impossible the task would be. Nevertheless, I think we should keep these misconceptions in mind and, whenever the oppor­tunity is favourable, do our best to gently nudge the customer’s thinking in the right direction. Who knows; we might score once in a while. J. L.’s routine faults But enough of the philosophising; its time to get back to the bench – J. L.’s bench, that is, where we left him last month running through some typical routine faults. More precisely, he had just solved an acute case of the warbles in a Sharp audio cassette deck. He goes on. The next job on the bench was another audio cassette tape deck, this time an Hitachi model. A note taped to the top of the cabinet said that the machine had been “wowing” for some time but had now stopped altogether. I soon had the cover off and began a close inspection of the works. There was nothing wrong with the power supply or the electronics. It seemed to me that this had to be another mechani­cal problem. In fact, when I turned the power on, I noticed that the capstan flywheel made a short movement in the direction of normal rotation but then sprang back to its original position. It was obviously being jammed by some very elastic medium. I examined the cassette well, half believing that it was another pinch roller, like the last job. It wasn’t but it was another perished rubber part. This time it was the main drive belt. This is a flat belt, about 5mm wide. It had softened and stuck to the motor pulley. When the motor started, it stretch­ed the belt and wound several layers around the pulley. The belt was a write off, so I had to remove the motor and its mounting plate, fit a new belt, then reassemble the motor and test the unit. It wasn’t quite as easy as it sounds, since the remains of the old belt were very difficult to remove from the motor pulley. I had to use copious quantities of spirit to soften the deposit, then scrape and wipe until it was all gone. Following these two audio jobs, it was back to colour tele­vision for another brief exercise. This was a 50cm Philips set fitted with a KT2A-2 chassis. The owner reported that the on/off switch must be broken because the set would not switch on. I don’t know why customers always blame the power switch when a set won’t start. There are a hundred other things that could be blamed but it’s the power switch that cops all the stick! (It’s obvious J. L.; when they press the switch nothing happens – so the switch must be at fault!) On this occasion, I was soon able to absolve the switch simply by putting my ohmmeter across the active and neutral pins on the power plug. The meter showed infinity when the switch was off and a hundred or so ohms with the switch closed. Next, I went to the power supply section on the horizontal output board. The supply configuration in this set is most unu­sual. It’s effectively two separate DC supplies, connected in series by a Triac that’s triggered by a variable pulse derived from one of the bridge rectifiers. It’s a funny arrangement and one that is not at all easy to service if any part of it breaks down. In this case, I was lucky; I found the cause of the trouble after only 10 minutes’ work. I established that there were correct voltages being sup­plied from the bridges but very little at the output. So it seemed reasonable to assume that the regulator was at fault and my usual practice is to test transistors and diodes first. I was only a few minutes into the testing when I noticed a dry joint at one of the regulator transistors attached to a large heatsink. It didn’t look bad enough to be totally open circuit but it was and a touch with the iron soon restored the set to working order. So much for a “faulty” power switch! The last job for the day was a General Electric portable colour TV set, said to have an intermittent colour problem. The problem was intermittent but not in the usual sense of the word. When first switched on, the set would come up with a good black and white picture. Then, after anywhere from 30 seconds to five minutes later, the colour would snap on and stay that way as long as the set was left untouched. Switching off or changing channels would lead to a repeat of the black and white process. The fault was easy to diagnose. It was caused by maladjustment of the sub-carrier oscillator. The oscillator was tending to run off-frequency and the AFC circuit was having difficulty pulling it back. The service manual gives details of the adjustments required and it took only a minute or two to effect a complete cure. The adjustment calls for the AFC circuit to be disabled so that the colour can be “floated” by tuning the oscillator. As the adjustment is made, the colours run first one way then the other. The correct setting is between the two runs, where the colour just stands still. When the AFC is re-enabled, the picture should be in colour and should stay that way. In this case, it did and the set went home to a happy customer. After that, it was time for me to go home. Not every day is as straightforward as this one. But then, if I didn’t get an occasional day free from the bad SC jobs, I’d go stark raving mad. VIDEO & TV SERVICE PERSONNEL TV & VIDEO FAULT LIBRARIES AVAILABLE AS PRINTED MANUALS $90 EACH + $10 DELIVERY BOTH MANUALS VIDEO & TV $155 + $15 DELIVERY OR AS A PROGRAM FOR IBM COMPATIBLES $155 + $10 DELIVERY FOR MORE INFORMATION CONTACT TECHNICAL APPLICATIONS FAX / PHONE (07) 378 1064 PO BOX 137 KENMORE 4069 AUSTRALIAN MADE TV TEST EQUIPMENT 12 Months Warranty on Parts & Labour HIGH VOLTAGE PROBE Built-in meter reads positive or negative 0-50kV. 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Integrated circuits, resistors, capacitors, transistors, diodes, valves, varistors, etc. Any brands Let us save your valuable time Contact us now on 833 1342 We are also distributors for Electrolube lubricants and chemi­cals Hakko - desoldering & soldering irons; SMD tools; replacement parts NTE - replacements semiconductors 2/87a Queen St, St Marys, NSW 2760. Phone (02) 833 1342 Fax (02) 673 4212 December 1993  61