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SERVICEMAN'S LOG The case of the worn video heads I doubt if anyone will deny that a serviceman has to be a good detective - not in the mould of the popular fictional detectives, but a detective nevertheless, who must observe clues, probe history and find a solution to what is sometimes a very obscure problem. Just how much detective work is sometimes involved was brought home to me quite forcibly by a recent experience. More than that, it emphasised that the vital clue is often way outside one's normal line of technical thinking. The story really started about 8 years ago; and that, in itself, gives some idea of the complexity of the problem. It involved one of my long standing customers who, at that time, purchased a National NV-370 video recorder from my dealer colleague. And I hasten to add, the NV-3 70 was and still is a highly regarded machine. Many are still working with little or no service after many years of hard work. I knew little about this transaction at the time, or of the subsequent events, because I was not a National service agent until a couple of years . later. But I was able to piece the story together eventually. Faulty heads When the recorder was sold it carried a 3-year guarantee. So, when it gave trouble after about 18 months, the owner took it back to the dealer, who returned it to the National service department. The fault was diagnosed as faulty video heads and these were replaced, no charge. Some time after this, I acquired the National service centre classification. So, when the machine failed again, it landed on my bench. And it was only then that I learned of the events I have just related. A little more than another 18 months had elapsed by 26 SILICON CHIP then , so it was no longer under warranty. And again, it was video head trouble. As it came to me, the suggestion was that they needed cleaning, and there certainly was a substantial build-up of tape oxide and other foreign matter. But it quickly became clear that there was more to the problem than that. In fact, the heads had had it. I advised the owner, via my dealer colleague, and quoted for a new set of heads. Naturally, they weren't very TETIA TV TIP Hitachi CTP-229 (NP8CA Chassis) Symptom: excessive brightness and not enough control to bring it down. A "sort of" picture could be obtained by reducing the screen voltage but this revealed heavy shading on the left hand side of the screen. Cure: C719, a 4.7µF 250V electro, open circuit. This capacitor is a bypass on the 180V rail feeding the video output transistors. This fault is rather like a screen-voltage problem but the clue is that with this one there are no retrace lines visible. TETIA TV Tip is supplied by the Tasmanian branch of The Electronic Technicians' Institute of Australia. Contact Jim Lawler, 16 Adina St, Geilston Bay, Tasmania 7015. happy about this, even though they had not paid for the first job. Anyway, they eventually decided to go ahead and the job was duly done. That was OK as far as it went but I was puzzled as to why two sets of h eads had failed in such a short time. The first set, yes. Such premature failure is rare but it does happen. But the second could hardly be described as coincidence. It suggested that there was something peculiar to the machine's environment or manner of use which was responsible. But what? The question of tape quality had already been investigated - on both occasions - and all the tapes used had been well known and reliable brands. So that ruled that out. I had been to the customer's home on other service matters several years previously and my impression was one of a normal, neat and tidy, well kept house. Dirt road The only suspicious aspect was the house's location. It was on the outskirts of the suburb, alongside an unsealed road. And there was a fair amount of traffic on the road , some of it quite heavy in the form of trucks on their way to the local tip. I imagine that they would have been kept quite busy coping with the dust , particularly in dry weather. So was that it? Perhaps, but how could one be sure? And, unless I could be sure, I would have hesitated to - in effect - accuse them of not doing an adequate job of house cleaning. (It takes a brave man to do that). So that was as far as my thoughts went at that stage. Another two years went by, and then the machine was back on my bench again. And again it was the video heads. But there was more this time. The sound head and the control track head were also faulty and there was some damage to the cabinet. I gained the impression that · the ma- 1 ~~ '-J~ ~ t:i ~-- s:-.~~ ,..._ & ·-r,.u~:Rc;. ~rAINL.. '-( 0 "1/ w,qs A SUBS,-AN1"'1Al- °BUIL--D·UP OF TA'P~ OX1De &. 011H~R FO~c-f6N MA1fc-R 0 .. chine had had a pretty hard life. In fact, the customer readily agreed that it was worked pretty hard. "I reckon it would be used for at least three hours every day", he said. That adds up to a lot of.hours over two years . Nevertheless, I was still at a loss to explain this latest failure . More to the point was what to do about it. Video heads were still quite expensive and, with the sound and control heads , plus some replacement bits for the cabinet, I toted up an estimate of around $350. It was too much, of course. They wouldn't buy it and I couldn't blame them. Far better to cut their losses and put that amount of money towards a new, more modern machine. And that's exactly what they did. They went off to my dealer colleague and settled for a National Panasonic NV-G30 (significantly, they did not appear to hold any grudge against this brand). The NV-G30 is, in many respects , an updated version of the NV-370. It uses the same mechanical deck but is a more compact design and features the more modern infrared remote control system. (The NV-370 used a cord type "remote" control). And would you believe if:' - the NV-G30 was back on my bench within 18 months with faulty video heads. Strangely, the customers did not seem unduly perturbed; mainly, I imagine because the machine was still under warranty and it would cost them nothing. I also gained the impression that they now accepted that this was the norm for video recorders. A possible clue Privately, 1 was still at a complete loss to understand what was happening. But there is a severe limit to the amount of time and effort one can devote to any investigation. For the most part, one is limited to whatever information comes to hand; it is just not practical to go out and look for it. And so that's where matters rested until, quite by chance, another piece of information came to hand. In fact, two things happened almost simultaneously. First, the NVG30 came back again, exactly 19 months after I had fitted the new set of heads, and it was the same story; these heads had now failed. Shock is hardly an adequate word to describe m y feelings. For one thing I would have to confront the customer with this disturbing news and I wasn't looking forward to that. But there was also the feeling of utter frustration, knowing that there was something wrong but not knowing how to go about finding it. Th,m, even before I had passed on the bad news, the second thing happened. Another customer brought in a National NV-450, with the suggestion that the heads probably needed cleaning. This proved to be something of an understatement; it was extremely dirty. Most of the fouling was tape oxide but there' was also some suggestion of a gritty substance mixed with it which, initially, I was unable to identify. I gave the machine a thorough clean, then ran a test tape through it. It brought up a picture OK but the quality was a bit suspect; acceptable if you weren't too fussy but obviously down on new performance. Then I tried making a recording and the result here left no doubt ; it was grotty in the extreme. I decided to return the machine to the customer with a recommendation that it needed a new set of heads for any serious recording. It was then that I made the discovery. For some reason - which escapes me now - I put my fingers through the front opening into the cassette carrier area and, specifically, onto the bottom plate of the cassette carrier. And when I withdrew my fingers they were black. I rubbed my fingers over the plate again and produced more black. What was it? It wasn't tape oxide, nor did it seem to be normal house dust or fluff. I fished out the jeweller's loupe and, after some searching, found another more accessible deposit. It was on a plastic insulating strip near the power supply, covering some mains termi_nals. Getting in close with the glass - and feeling a bit like Sherlock - I studied the muck carefully. There was some house dust but this wasn't the main component. What caught my eye was a fine grey powder, almost as fine as talcum powder. Ashes to ashes What was it? It took me a while to wake up ; then it hit me out of the blue. It was some kind of ash , probably wood ash from a wood-burning room heating stove. But why were my fingers black, if the muck was grey? I suspected that, in wiping the muck MARCH 1991 27 the cause of the premature head failure, she volunteered the information that the video recorder normally sat beside the stove. So that was it; the problem was solved at last. Solved, that is, in that we now knew the cause. What to do about it was another matter and large! y in the hands of the owner. All I could do was advise. And the best advice I could offer apart from scrapping the stove - was to move the recorder as far away from it as possible and make up some kind of cover to put over the recorder when it was not in use. I also risked suggesting more frequent use of the vacuum cleaner around the general area during the winter months. The lady accepted the suggestion quite gracefully. And so a valuable lesson was learned, but learned the hard way. From now on, the first suggestion of premature head wear will send me snooping for fuel stoves of any kind . Maybe they are not all bad but one cannot be too careful. SERVICEMAN'S LOG - CTD ) ~Vi ~,, /..... ! ~I ,, The early days - -- • . ..:9a.off the carrier plate, I had concentrated it and made it look mu ch darker. Anyway, I was convinced it was wood ash . And I was almost right. When the customer came in to collect the machine, I asked him straight out if he had a wood burning stove. "We do have a stove but we don 't burn wood in it. It 's a slow combus.tion stove which burns coke. Why do yo u ask'?" I told him. And while I was explaining it all, my mind went back to the slow combustion coke stoves I had known many years ago . And as one who for a time had to clean up after them, I rated them as one of the messiest devices ever created. Perhaps that's an exaggeration but I'm convinced that they are totally incompatibl e with anything like a video recorder. So what abo ut the NV-G30 and th e 'NV-370 before it;·was this the answer 28 SILICON CHIP . here also? Now that I had been alerted, my mind went back to the visits I had made to the customer's home many years previously. And the more I thought about it, the more I was convinced that I had seen some form of room heating stove. And if I had seen it, it was most probably in the lounge room, along with the TV set, because that was where I would have been. The case cracked Of course, I had to contact. the customer eventually. The lady of the hous e answered the phone and accepted the bad n ews philosophically; I suspect she was getting used to the idea and half expected it anyway. Then I posed the question , did they have a fuel stove anywhere in the house? The answer was yes. They had a wood-burning room heating stove in the lounge room. And when I explained that I believed that this was Naturally, I have already passed this story on to several colleagues. And that prompted an interesting recollection from one of them. It goes back some 25 years, to the time when video recorders, even at top professional level, were a rarity and a very expensive one at that. After many abortive attempts to solve the problem of providing adequate tape-to-head speed - usually by the brute force method - it was Ampex who cracked the problem with a (literally) lateral approach . The result was their quadrature head system, with four heads, 90° apart, travelling at right angles across a 50mm wide tap e. I remember this well because I was privileged to see a demonstration of the first one in Australia, at Channel 7 in Sydney. This was while the local engineers and the Ampex representative were fussing around preparing the machine for its on-air debut in couple of days time (which was a complete success, incidentally). While musing thus, I realised that it now comes as a shock to think that there was a time when there was no such thing as a video recorder. Now they are nearly as popular as TV sets . We've sure come a long way. But enough of such nostalgia; let's get on with my mate 's story. He had a business in one of our country areas at the time, and was friendly with the chief engineer at the local TV station. An d this was one of the first, if not th e first, country station to invest in one of those Ampex recorders. The price tag, incidently, was well into the 6-figure mark! Special room Acting on Ampex's advice, a special room had been prepared for the machine, fully air-conditioned to contro l temperature, humidity and, particularly, dust. It had also been very well sound-proofed. So the machine was duly installed and performed right up to expectations - or at least it did initially. Then, after about 12 months of use, trouble occurred and was traced to worn heads . Nobody was very happy about this because they had been led to expect much longer life, in terms of actual playing hours. However, they shrugged their shoulders and arranged to have a new set of heads fitted. And this ran into a 5-figure sum. Anyway, the new heads were fitted and all went well fo r about another 12 months . Then the heads failed again . There was no shoulder shrugging this time; the panic button was pressed and it was all hands and the cook - plus Ampex - lined up to solve the problem. Well, it took some detective work in this case also. On the face of it, it appeared to be the perfect environment , so what had gone wrong? It turned out to be part of the soundproofing, at least indirectly. The room had been lined with acoustic tiles ; squares of Canite, or similar material, with a pattern of small holes drilled through them. The holes were supposed improve the sound absorption properties; ie, reduce reflection. In particular, these tiles had been used as the ceiling. Then, above them, for both thermal and acoustic insulation, had been laid rockwool bats. Now, as anyone who has ever handled this stuff without gloves will testify, it is h ighly abrasive. And tiny particles had been working their way through the holes in the tiles and, while not large enough to be noticeable, had found their way into the TRIM machine and played havoc with the heads. So that solved that problem. But it was a very expensive exercise, particularly by the money values of those days. Indeed, it might make the cost of domestic repairs seem trivial - until you realise that a couple of hundred dollars is still a lot of money for Bill Bloggs. Another video recorder To finish off, here is another sad tale about a video recorder. This was a Fisher FVH-P520; a model which is now some 8 or 9 years old. Truth to tell, there are not many Fisher machines about; I would probably handle about one a year. The original Fisher was made by Sanyo, in Beta format. Since this machine turned out to be in VHS format, I'm not sure whether it was actually made by Sanyo or simply marketed by them. But, as it all turned out, this was of little consequence. It was brought in by a lady, a new customer, with the complaint that it produced sound but no picture. Initially, I suspected fouled heads but I did notice one thing as I took deliv- E-1 LAMINATED POWER TRANSFORMERS PCB mount ex-stock in sizes from 2.5V A to 25VA with secondary voltages from 2 x 6V to 2 x 20V. Triple output models also available for logic circuits. Chassis mount manufactured to order in sizes from 2 .5VA to 1 KVA in E-1 and C core. PCB MOUNT STOCK RANGE CHASSIS MOUNT TO ORDER OUT ~~ '"SUl/\l lm; OUTER W H1;0: .. G - We are the largest ex-stock supplier of toroidal power transformers in Australia. Our standard range consists of the U.K . manufactured ANTR IM range in 10 VA sizes from 15VA to 625VA. All have a single 240V pr imary and dual secondary windings ranging from 2 x 6V to 2 x 55V. Our local manufacturing facilities supplement this range by manufacturing specials to order. Models are available from stock to suit most project kits. Comprehensive data sheets are ava ilable on request. Enquiries from resellers and _manufacturers are welcomed . Prices are extremely competit ive and generous trade discounts apply for quantity. 90 George St.. HORNSBY NSW MARCH 1991 29 spikes sh ould h ave ripp ed my tap e to pieces , even severed it. Yet neith er visibly or by playing it on anoth er mach ine, could I find any sign of damage. That's a mystery for whi ch I have no answer. I rang the lady and broke th e bad news. And to cover myself, I asked h er to come in and see the damage fo r h erself. When she did , I showed h er what I had found and pulled the covers off a good machine to indicate what it sh ou ld be like. She accepted my explanation readily enough. How di d it h appen? Had it been to another serviceman? No, sh e was quite adamant on that point. Her story was that they had acquired the mach in e by some kind of swap deal. It h ad worked w hen they took delivery, and for several weeks after. Then, suddenly, "it didn't go". That was all she knew. It could have been h er husband but sh e was more inclined to blame the teenagers of th e household. At least that was her story. So there it was - an otherwise good machine which will now finish up on the tip. What a waste. Here's hoping I have S()!l18 brighter stories next month . SC SERVICEMAN'S LOG - CTD . ery. This is a top loading model and one of the screws in the cassette carrier cover was missing. The alarm bells may have tinkl ed a little then but they didn 't actually ring. Later, I set it up and pushed in an odd tape I use for testing. The lady was right; not a sign of a picture, though sound was normal and seemed to be at the right pitch. I extracted th e tap e, removed the cassette carrier cover, then the main top cover, and fin ally the steel screen over the head drum (another screw missing). And what a mess I found. No, it wasn 't foul ed heads or anything like that; someone had been there before me. And if anyone qualified for a striped apron award , it was him. Whether it had been another serviceman, or just some do-it-yourself type, I had no way of knowing , but I certainly hop ed it wasn't a "professional". The two screws which secure the head drum to the main assembly were missing , the terminal board in the centre of the h ead was broken, and some of the leads to it w ere broken. But the best - or worst - was yet to come. Th e "someon e" had tri ed to remove the drum . An d, lacking both the skill and tools to do the job, h e had tried to prise it off with a screwdriver. The most obvious result was severe damage to both th e rotating drum and the matching lower drum . In fact , there were several n icks in th e edges of both drums which had left small sharp raised spikes. Nor was that all. I spun the drum and it w obbled around like a drunken sail or w ith one short leg. The shaft was bent. A total w rite-off So that was it; a total write-off. 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