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Copping it right in the neck As a disgruntled colleague once commented, the worst thing a TV serviceman has to deal with is the customer. While unfair to the majority, I have to agree that a few can be very frustrating. They either don't trust you, insist that they know what's wrong, provide vast quantities of irrelevant data or, worse still, cover up the truth. Those thoughts were prompted by one of the most unusual and puzzling experiences that I have encountered for a very long time. In fact, it was like nothing I have ever encountered before. More to the point, it has left me wondering whether my trust in an old and valued customer has been misplaced. The set involved was a General GC181. It was sold to the customer by one of my dealer colleagues in January 1979, making it close to 10 years old when this incident occurred. I covered the warr~ilty service for the set and have serviced it ever since. The truth is it has not needed much attention, having developed only two serious faults in that time. The first one involved a total failure and turned out to be a fairly common fault in this set. There is a 0.1µ,F 1000V capacitor across the mains at the switch and this is prone to breakdown, taking out the main fuse. But this can be a trap for young players. The type of capacitor used is often one of the self-healing variety and when the serviceman examines the set, there may not be any obvious fault which caused the fuse to fail. In desperation, he may be tempted to simply fit a new fuse and put the set back into operation. The catch is that once these capacitors fail, the chances are that they will fail again in a very short time. So the customer is saddled with a nuisance call within a few months, or even weeks, and the serviceman's reputation suffers accordingly. The correct procedure is to replace the capacitor, preferably with a more reliable variety. The other fault occurred quite recently. The customer complained of poor picture quality and this turned out to be loss of focus· another common problem with thi~ set. This is due to failure of the focus pot, caused by internal arcover and resultant destruction of the element. I fitted a new focus pot and all was well. But these are asides, even though mention of them may possibly help some readers. The real story is yet to come. The owner Front view of the General GC181 set, showing how the phosphor was stripped from the screen. Note the damage to the shadow mask which is visible behind it. There was a lot of damage to the chassis as well. 54 SILICON CHIP But first a few words about the owner because this is important to the story. He is a bachelor, now retired, who lives alone. I first met him when he bought the set and we have met socially on many occasions over the years. In short, we have become quite friendly. For his part he turned out to be one of those intensely loyal customers who boasted that he would never let anyone other than myself ever lay a finger on his set. Such loyalty can be both touching and embarrassing; the more so because it may be difficult to justify. (I'm really a very 'umble person). This rear view shows the broken tube neck and the gun facing in the wrong direction. The gun has been re-positioned slightly to give a clearer picture but is essentially as I found it. happened at that stage but one thing was obvious: the tube had So that is some of the background been "let down to air" with a rush; against which this story is set. It a rush so great that the air had began when the customer phoned stripped the phosphor from the me to say that the set had screen and propelled some object developed what he described as "a against the shadow mask with conblack flower in the middle of the siderable force. screen". I did a bit of a double take My guess was that this was the on that, trying to visualise what gun and that it wa s now lying inside kind of faulty picture tube voltage the tube at the bottom of the screen. would cause what I took to be a As it turned out, I was only half dark patch on the screen. Not havright. ing much success, I simply said I'd My first step was to remove the be around to look at it as soon as plastic back from the cabinet and possible. · try to work out what had happened. What I found, of course, was This ba ck is held on with seven something quite different, and I screws: five machine screws which have no doubt that the reader is · mate with metal inserts in the way ahead of me. One glance was cabinet woodwork and two self tapsufficient; the phosphor had been ping screws which mate with the stripped from the centre of the antenna terminal panel. I mention screen in a roughly circular patch this because it is significant in about 12cm in diameter, with jagg- regard to what comes later. ed edges which had reminded the A proper mess customer of the petals of a flower . I found myself looking at a right Through this opening could be proper mess. The neck of the picseen the shadow mask and it was ture tube had broken off behind the also in a bad way. It had been hit yoke, about where the purity from behind, with a prominent dent magnets sit, and was lying in the in the centre and a vertical split almost as long as the diameter of bottom of the ea binet. But the real surprise concerned the "flower". the gun. I had no reason to doubt it I didn't know exactly what had Black flower had hit the shadow mask but I was wrong about it sitting in the bottom of the tube. It was sitting in what was left of the neck but - and this is the weird part - the front of the gun, which normally .faces the screen and carries the getter assembly, was pointing out of the back of the neck. The accompanying photograph illustrates this better than words. So what had happened? On the face of it, it appeared that the gun, either before or after it hit the shadow mask, made a 180° turn and came out the tube front-end first. And significantly, subsequent examination of the gun revealed that the pin end had been very severely mutilated. So had this hit the shadow mask? That was not all. The neck board had of course been separated from the gun as the latter shot inwards and had been broken in two as well as suffering some other minor fractures. I made a mental note that if necessary, it might be possible to repair it, assuming no replacement was available. But what really caught my eye was a metal bracket at the right hand end of the chassis. This is made from 1.2mm (18 gauge) mild steel and is about 19cm high and 15cm wide. It supports the tripler, an aluminium heatsink for the power supply chopper transistor, and sundry minor components. And it had obviously been dealt a pretty solid wallop, which had given it a severe twist. Once again, the accompanying photograph tells the story better than words. There didn't appear to be any damage to any of the components on this panel but what intrigued me was how it had been bent. The panel is quite substantial, so much so that an attempt to straighten it by hand was abandoned. I'm not saying I couldn't have done it but it would have been a painful exercise. Rather than speculate, I turned to the customer for clarification. When had this happened and how? He shrugged his shoulders. All he could tell me was that he had used the set one evening, not bothered with it the following morning, gone to his golf club for lunch and a round of golf in the afternoon and JA NUARY 1989 55 : ' \ \ " =-'- lt?f!l//i \.\~'t) Spontaneous implosion Which didn't help much. It could have happened at any time over a period of some 18 hours and there was no indication as to how it had happened. On this basis I had to assume it was a case of spontaneous implosion, even though I had never known a tube to implode in this manner. From the faceplate, yes; but not from the neck. And if it was such an implosion, how could this account for the damage to the metal panel? As far as I could see the only "missile" that could have caused this was the neck board, thrashing around on the end of its cables after it become detached from the gun. But as can be seen from the photograph, the SILICON CHIP ' . ~1~;;~~~-:.~~;~:-:--.. . .-" NE.VS:.R \<.NOWN A -rue£ 1~ T'-IIS MANNE~ discovered the damage only when he went to turn the set on for a 6 o'clock news session. 56 "-=...._"''""" . ~~ ... ~ J't I. ,, panel is bent towards the picture tube neck, so that it would have had to have been a whipping action to bend it that way. One problem with this theory was whether there would have been enough room for all this action, with the cover in place. There certainly would not have been while the tube was intact but it might have been possible after the neck broke off. Another problem concerned the simple ballistics of such an action. Could something as light as the neck board acquire enough kinetic energy to bend such a substantial piece of metal? Sure, there was a neat puncture in the plastic cover on the neck board which could be made to mate up with the top corner of the panel, supporting the idea of an impact between the two. But there for the moment was -- -~-- --· .J. ...·c.,, __ .. ' ' \ \ \ <at>.\~(. ,...0 where I had to stop speculating. The customer brought me back to earth with the obvious question, "Is it worth fixing?" I did a few mental calculations. There was the cost of a new tube, with no allowance for the old one, the cost of fitting it, and repairs to or a replacement for the neck board. Allowing for any other minor damage but assuming there was nothing serious, I came up with a ballpark figure of $400. I added that if he decided to go ahead, I would need to make some more tests and checks before risking the cost of a tube. But he cut me short. "It's not worth it. The set is 10 years old. I'd rather put that money towards a new one. You can have the old one for bits if you like." So we left it at that. I loaded the set into the van, took it back to the shop and arranged to get photographs taken. Then I decided to take a closer look at it, for a couple of reasons. First, I thought that it might be possible to salvage the set, at least on personal basis. If I could score a tube, perhaps from a set written off for other reasons, I might have a set good enough to use as a monitor, or even to donate to the local retirement village charity. Second, I was still puzzling over how the damage had occurred. Perhaps a closer inspection might provide a clue. So a few days later, during a slack period, I made an effort to fire up the set. At least I hoped to get sound out of it and confirm that most of the circuits were working. Also I wanted to measure the EHT to see whether it had gone high and possibly punctured the tube. This is not unusual, though I have never known a tube to disintegrate for this reason. Dead as a doornail But the set did not respond; it was quite dead. I checked the mains fuse and found it intact, so I decided to slip the chassis out for a closer look. This is quite easy, it being held with a couple of simple plastic clips. In fact, the chassis is little more than a rectangular metal frame which holds the main (mother) board horizontally in the bottom of the ea binet, the whole assembly measuring about 33 x 20cm. And this provided the next surprise. It was just as well the customer had decided to cut his losses because there was no way that the set could have been salvaged. In order to understand what had happened it is necesary to describe this part of the set in some detail. To the left of the picture tube, sitting above the mother board but with their lower edges almost in contact with it, is a nest of four vertical boards held in a plastic frame attached to the rear of the chassis. From the left these are the chroma board, video board, vertical board and the horizontal board. They are all 80mm high and range from 120mm to 75mm long. ' [ c,w;;,,,,&,,., , , :Iii This picture shows the top edge of the bracket, to the right of the tube, and the manner in which it was bent. Note that it has been bent towards the tube which only adds to the mystery. And at least one of them had received a mighty wallop on its upper edge, forcing it down against the mother board. The vertical boards appeared not to have been damaged, but they had made a horrible mess of the mother board. It was cracked from front to back, with another crack extending from approximately the centre of the main crack to the left hand edge. There is no way that the board could have been salvaged; it was a write-off. All of which served only to deepen the mystery. What had struck the blow? As with the bent bracket, the most likely culprit seemed to be the neck board, TETIA TV TIPS Hitachi CEP288 Symptom: Very bright picture, no colour and retrace lines. Subbrightness control will reduce brightness somewhat, but not enough and still with no colour. Cure: Check voltage at Test Point 11, near the chroma delay line. This should be about 1 .5V. If it reads OV, suspect a short circuit to ground inside one or other of the transformers T552 or T553. thrashing around as a result of the implosion. But as before, it was hard to accept that it could acquire enough energy to do so much damage. It was all very puzzling. I had to admit that the theories I had evolved were not very convincing but were the best I could come up with if I accepted the customer's version of events. A cynical colleague Later, I had an opportunity to discuss the matter with a colleague and to show him the physical evidence. Being a cynical type and not knowing my customer, he had no doubts about what had happened. His theory was that someone had removed the back for what they regarded as a legitimate reason, such as looking for a fuse if the set had failed. Then while the set was in this vulnerable condition, an accident had occurred; something heavy had fallen across the back of the set, from right to left, first bending the metal bracket, then breaking the neck off the tube and finally forcing the vertical boards down onto the mother board and wrecking it. As he summed it up: "I don't believe that that kind of damage could have JANUARY 1989 57 SERVICEMAN'S LOG HOW 11-1£, e:A~S ])()tJT 6'!:.L.\EVE A WO'RO YOU T£.L.I.. HIM,•• NO,~ occurred unless the back had been removed". And I have to agree that on the physical evidence, such a scenario makes sense. But it just doesn't fit the personality of the customer I know. He would be the last person in the world to delve into the back of a TV set and he is adamant that there was no one else in the house at a time when this could have happened. Break and enter? Vandalism? The house was well secured while he was out and there was no sign of forced entry. In any case, what vandal is going to take the trouble to remove the back in order to the wreck the set and then carefully replace the back afterwards? And when I say carefully, I have 58 SILICON CHIP in mind those seven screws I mentioned earlier. Several do -ityourself types, as well as a few of my colleagues, have been caught out by these. Superficially they all look the same; same heads, same diameter, same length, same colour. So it is almost inevitable that the first time someone handles them they will mix up the metal threads and self tapping threads, with resultant thread butchery. But there was no such butchery. If the back was removed and replaced whoever did it was very careful or very lucky. It's not conclusive evidence but just one more puzzling factor. So which theory is right? Was it all the result of a spontaneous implosion, or was the set mucked about with? And if the latter, by whom? And why the secrecy? I'm afraid your guess is as good as mine. Murphy takes a holiday Well, after all that inconclusive theorising and speculating, here is something much more down to earth. It concerns two Sharp CX-1461 34cm sets, both with the same fault - well almost. An alternative to the above title could be: "The same only different" . In the first case the customer turned up at the shop with the set and complained that it was completely dead. Judicious questioning elicited the fact that it had been cranky for some time, in that it would not function when first switched on but could be made to run by operating the on-off switch several times. Once running it would give no further trouble during that run. As a result of this observation the customer inevitably concluded that the on-off switch was faulty. Naturally I doubted that it would be that simple and said as much to the customer. Whether I convinced him or not I don't know but he agreed to leave the set with me. And would you believe it, within hours of that encounter in walked another customer with the same model set and almost the same story: the set would function sometimes when switched on but not always. It also could sometimes be made to function by repeated operation of the on-off switch. And it had become more cranky of late and now had failed completely. Not surprisingly, this customer came up with the same diagnosis as the previous one; the switch must be faulty. I expressed the same doubts as before. Privately, I was daring to hope that both sets had the same fault. That would really put the day's work in the black - and give Murphy a good solid kick in the pants, to boot. In any case, it seemed like too good a chance to miss so I pushed the other jobs to one side and selected the second of the two sets for a preliminary check. At first switch-on it was quite dead, at least superficially. On im- lcONrusTI 0 41 8 3CE [ t~ PF"2 R'!l2~ 1 . 71( ! l/2WI PWB - 0 DUNTKl77 Fl'!l2'!1 2,21< !l/2WJ Relevant portion of the CX-1461 circuit. Note the IC (IC701) which replaces the regulator transistor and associated discrete components. pulse I activated the on-off switch a couple of times and, hey presto, the set burst into life. Of course, it could have been a faulty switch but I was basing my doubts on the fact that I had never had to replace a switch in this model and that the switches used in most modern sets are particularly reliable. It is several years since I had a switch failure and that was in an old Decca model 33. Supply problem So, putting aside the switch theory for the moment, all the indications were that we had a power supply starting problem. And significantly, once the set was running it produced a first class picture, right up to standard in every respect. The idea that it was a starting problem reminded me of my story in the November 1988 issue of SILICON CHIP, involving another Sharp set, the slightly later CX-1480 model. It too had a starting problem. My recollection was that the two circuits were similar and I wondered whether this was another case of 120kn resistors going high. Unfortunately the manual showed that the power supplies were quite different and that the 120k!J resistors did not even exist. The manual did devote a couple of pages to a description of how the power supply worked and this looked promising at first. But that promise was not fulfilled. The explanatory circuit used differed from the main circuit in that a number of components were omitted. And the text, as well as mixing up some terminal connections, was written in, at times, incomprehensible Japlish. The main thing I learned was that an IC (IC701, IX0205CE) was used in place of the usual regulator transistor and associated components. This combined three transistors (error detection, driver and switching transistor) plus the reference zener diode and four resistors in a single TO3 package but with four terminals. So much for the theory. It was time to pull the chassis out and make a few measurements. When I switched it on this time it refused to start, which was actually a help. The first check was the voltage out of the main bridge rectifier, across the 22µF electrolytic, C708. This proved to be normal, thus ruling out any lingering doubts about the switch or other components up to that point. From here I traced the voltage up to pin 2 of transformer T701, then to pin 4 and finally to pin 1 of IC701. continued on page 66 JANUARY 1989 59 · THE WAY I SEE IT- CTD (3). Applied to power lines and equipment, the term "radiation" has connotations of an implicit hazard by association with nuclear and high-power RF energy. In fact, 50Hz energy has a wavelength of around 6000km, and any "radiation" detectable within several hundred metres of the source is a near-field phenomenon and should be regarded as such. The author quantifies the magnetic and electric fields at ground level under typical high voltage transmission lines, pointing out that they tend to cancel down with proper design and phase balance. They are normally small compared with the Earth's static field and the electric fields present in thunderstorm conditions. In private homes, the 50Hz magnetic field can be greater than under power lines, especially near certain appliances and neutral/ earth links. A high, though not necessarily hazardous, electric field exists close to some electric blankets, according with our advice in the September issue to avoid leaving them switched on for long periods while you sleep. Nature, man-made and us On the subject of "Field Effects on Natural Ecosystems", Callaghan acknowledges some critical reports but suggests that they are mostly flawed. Serviceman's Log - SILICON CHIP It has been claimed, for example, that the growth rate of certain species of trees adjacent to high voltage lines is accelerated but this could be the result of opening up the easement area. Equally, a conflicting observation that the growth rate is sometimes retarded could be due simply to residual corona damage to the tips of the foliage. Bird migratory patterns do not appear to be affected by the field. Small animals are partially shielded from the electric field by the ground cover; for large animals, the changed forage conditions appear to be more significant than field effects. The performance of honeybees appears to be diminished somewhat by high electric fields but this can be mitigated by shielding the actual hive. And so on. His conclusion: "There is currently no scientific evidence of any environmental effect of 50Hz electric and magnetic fields on nature, above the negligible level". In the area of interference with man-made systems, the power line engineer has an admitted responsibility to minimise arcing and corona effects, which could affect communications systems. As well, due attention must be paid to possible magnetic and electric induction, earth current loops, &c. The latter section of the paper deals extensively with "Field Ef- ctd from page 59 So far, so good. At this point it appeared that with only a few components likely to be involved, a check of each component in turn might be the best approach. Remembering the faulty resistors in the CX-1480, I began by checking the resistors. R710 (along with diode 709) was disconnected first, then R709, R705 and 706. All checked OK. The next suspects were the electrolytic capacitors. I lifted C713 (100µ.F) and it checked OK. Then I lifted and measured C711 which connects to pin 4 of IC701. Supposedly 3.3µ.F, it measured only 66 . about 0.1µ.F. Eureka! Yes, that was it. A new 3.3µ.F capacitor was fitted and at first switch-on, the set came good immediately. And it continued to do so for a large number of switch-on cycles. I considered the point proved. In fact, I can now reveal that that particular capacitor is not even shown on the explanatory circuit mentioned earlier. Dare to hope So, one down, one to go. Dare I hope? Naturally I went straight to that capacitor. I unsoldered one pigtail from the board and as I fects on Biological Systems" and it is clear from the references that the author has taken due account of available literature. While a great deal of research has been undertaken since the 1960s, the findings again tend to be inconclusive. This despite the fact that, after 3-4 generations of exposure to power line fields, possible acute effects should have become selfevident. No long-term effects have ever been confirmed and no mechanism has been suggested whereby such long-term exposure could induce problems . Callaghan's overall summary: "Currently, the overwhelming opinion of the world's scientific/ medical fraternity is that long-term exposure to power line fields has not been shown to constitute a biological hazard to man". All this may be reassuring but is it the final word on the subject? Can we rest assured that she really will be right mate? I don't think so. If I'm conservative about miracle cures - Kira Voxes, shocking coils, organic germanium, &c - I feel much the same way about the environment. Even with the best of intentions our understanding of the environment is never quite unbiased or complete. The way I see it, in the pursuit of scientific achievement and technological progress, it's not a bad philosophy to always err on the side of caution. ~ lifted that end, the capacitor came clean away; the other pigtail was corroded where it entered the body and had obviously been making intermittent contact for some time. A new capacitor restored the set to normal operation, all in a matter of minutes. You don't get many breaks like that; Murphy will have a heart attack if he finds out. But as I commented earlier, the two faults were the same only different; the same capacitor but faulty for different reasons. The first capacitor had simply died of old age - a common fault with low value types - while the second one might well have retained its capacitance but suffered a broken lead. ~