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SERVICEMAN'S LOG All it needs is a new fuse Some politician – whose name now escapes me – once decreed that “life wasn’t meant to be easy”. I don’t know who he was blaming for this situation but from where I stand, there are two who share some responsibility: TV set designers & customers. OK, so that’s a sweeping statement. Only a few customers make life less than easy and not all set designers are to be similarly condemned. But there are always some and when they get together on the one job, it is no longer “life wasn’t meant to be easy” – it is life was meant to be hard. What started this grouch? Answer: the bloke who designed a Mitsubishi projection TV set (model VS-360A) and the proprietor of the local pub, who owned the monster. And I use that word monster advisedly; Frank­ en­stein couldn’t have done better. Granted, projection TV sets are not my strong point. More correctly, I have never had to service one before this, which probably didn’t help. It all started about 12 months ago with a phone call from the aforementioned establishment, explaining that they needed to have the set serviced. And the caller added, in a most authorita­tive manner, that “all it needs is a new fuse”. Well, that started things off on the wrong foot. People who insist that they have diagnosed the fault, particularly as stupid­ly as this, really annoy me. I felt like saying, “well you re­place the fuse”. Instead, I replied that maybe a fuse had blown but that this would be only the result of a problem; the cause of the fuse blowing was the real problem. But no, he wouldn’t have a bar of that. All the set needed was new fuse and he wanted me to come up and fit it. Well, there was no way I was going to be in that. I knew the set well enough by sight and I can remember when it was installed, about 10 years ago. It is in one of the lounges and there was no way that one could work on it there due to the lighting and general at­ mosphere, to say nothing of the equipment that I might need. So I had to explain that the only way I could service the set was in the workshop. What’s more, he would have to arrange delivery. I wasn’t being hard to get on with, just practical; there simply wasn’t enough room in my own van for the monster. And, in any case, there was no way I could handle the thing at either end; it was far too big and heavy for one person. On the other hand, I knew that the hotel had a utility and plenty of manpower, so that it shouldn’t be a problem for them. Well, he hemmed and hawed about that. He insisted that all it needed was a fuse and that I should be able to fix it in a few minutes. But I stuck to my guns; it needed to be in the workshop if I was to service it. He said he would get back to me. The monster arrives Fig.1: the layout of the projection system in the Mitsu­bishi VS-360A, as given in the manual. The internal shelf is not shown. It runs from the back, about halfway to the front, above the projection tubes. 76  Silicon Chip That was the last I heard of the matter for about three months. Then suddenly, one morning, he turned up with the monster in the ute, along with a couple of brawny blokes from the local football club who manhandled it (the monster not the ute) into the shop. And he was still insisting that all the set needed was a fuse. This record was getting a bit worn by now and I asked him on what grounds he based this assertion. And then it came out. It appeared that after I had insisted that I could only service the set in the workshop, he had called one of my colleagues. He had agreed to go to the hotel, had found a blown fuse, and made the appropriate replacement. And the set had come to life. And that, of course, proved that all it needed was a fuse. The only snag was, it didn’t work for long. I don’t know for how long – he was a bit cagey about this – but I strongly suspect it was only for a few switch-on cycles. Anyway, all he wanted now was another fuse fitted. And try as I might, no expla­nation would convince him otherwise. So I said, “leave it with me.” And so it was that I found myself saddled with the monster. Initially, I wasn’t quite sure how best to get inside the cabi­net, or what I would find when I did. I had no technical data of any kind and only the vaguest idea of the likely layout. The most obvious entry point at this stage was a rear cover which extended from near the bottom of the cabinet to a point just below the bottom of the top mirror, as shown in Fig.1. All I had to do was remove the 16 screws holding it. This provided some access but it was still quite restrict­ed. The main restriction was a shelf running the width of the cabinet from the back, above the picture tubes, and about halfway towards the front. Its main role appeared to be to provide sup­port points for the three projection tubes. These are high intensity types, about 150mm in diameter, and are mounted in line. The various boards, including the power supply, were mounted on the cabinet floor or on the sides of the cabinet. To get any kind of view of these boards, I had to get my head halfway into the cabinet, after which I was able to see two fuses on the power supply board and, with some difficulty, was able to extract them. They were 2A slow blow types located in the mains leads and, yes, one was blown. I suspected that the fault might be intermittent – or had been – so I fitted a new fuse and applied power. But the result was an instant splat. So much for the amateur diagnosis. At this point it was obvious that I could go no further without a manual. I rang the Mitsubishi service department and contacted a very helpful staff member. He confirmed that a manual was available, price $36, plus $6 for postage. I also took the opportunity to discuss access from the front of the cabinet. I suspected that a front panel could be removed and, in fact, had noted that there seemed to be small cover missing from the bottom of the cabinet front and that there were two large bolt heads in this area. While it seemed likely that these were holding the front panel, their size suggested that they might be also May 1995  77 SERVICEMAN’S LOG – CTD Fig.2: this diagram shows the mains, power transformer & voltage selector wiring in the VS-360A. The voltage selector selects the appropriate tap on the power transformer. holding something larger. I had no desire to undo them and hear three picture tubes crash to the bottom of the cabinet. I needn’t have worried. The Mit­ subishi technician confirmed that these were to ones to unscrew. He then asked me what the problem was. When I explained that the set was blowing mains fuses, he didn’t seem all that surprised. And he went on suggest that I should check the power transformer for a brownish goo or varnish with which it might be covered. Apparently this substance can cause corrosion problems and, in fact, I can recall something similar which caused trouble in a video recorder. Anyway, he suggested that this may have caused a tracking problem and that it might be cured by scraping away any obvious track. Well, that was a help. I ordered a manual and, while wait­ing for it, took the technician’s advice and unscrewed the two bolts in the front. This freed the front panel which extends from the bottom up to various user controls beneath the screen area. This provided much better access but there was still a mass of boards, interconnecting cables, plugs and sockets, which I had to sort out. I put it aside until the manual arrived. 78  Silicon Chip When it did, I was able to sort things out in a little more detail. The horizontal and vertical output boards covered a large part of the cabinet floor. And, looking from the front, the power supply board was on the left, tucked in behind them. The main component, the power transformer, weighing several kilograms, was bolted to the cabinet floor. Other parts of the power supply were mounted on brackets. Screwed to the side of the cabinet, on the left, in front of the power supply, was a large board carrying the convergence circuitry, and screwed to the side of the cabinet on the right was the signal processing board. Power supply Having sorted all that out, I faced the real task of trying to track down what was obviously a short circuit. The accompany­ing circuit shows the relevant part of the power supply. To the right of centre is the power plug, a two pole on/off switch, and a plug/socket combination marked BA. Next in line are the two fuses already mentioned, while a voltage selector socket at extreme left connects to the transformer primary via plug/sockets BC and BB. There is also a second, smaller transformer at extreme right, which is fed via plug/socket BD. It is part of the remote control system. It was one of the first things to be unplugged. The main transformer primary is on the lower side of the core, with 200V, 220V, 240V and 260V tappings. The secondaries on the upper side connect to various plug/socket combinations. This arrangement of plugs and sockets was doubtless intend­ed to simplify assembly and servicing and it does up to a point. The difficulty was to identify all of these in cramped condi­tions, at least for someone tackling it for the first time. As a result, I spent considerable time and a fair amount of physical effort – to say nothing of scoring a few barked knuckles – sorting out all these connections and making sure everything was disconnected from the transformer secondary. When finally satisfied that this was so, I pulled plug/socket BB apart, which gave me direct access to the primary tappings. I then made up a dummy power lead, complete with fuse, and connected it directly to the common and 240V taps. An instant splat Then came the moment of truth. I plugged it in and switched on. Again there was an instant splat. And that settled it; it was the transformer and it had to come out. Whether it could be salvaged or not still had to be determined. Again, the problem was mainly physical. As already men­tioned, the transformer was bolted to the cabinet floor, which meant that I had to fit a spanner at both ends; one in the cabinet and one underneath it. There simply wasn’t enough space under the cabinet and I finished up having to tilt it and prop one side up on a couple of wooden blocks. Even then it a was tedious procedure but I eventually had it free and was able to pull it out and set it up on the bench. And the Mitsubishi technician was right; it was covered with a brown varnish and there was a dark patch between the primary terminal lugs. I spent some time scraping all this discoloured varnish away, then tried it again with the dummy lead. But it was no use; there was another splat and another fuse was written off. I A shocked customer I had some doubts as to whether the hotel would accept this. And I wasn’t far wrong. They were clearly shocked at the figure but I pointed out that there was really little option. If they were not prepared to spend that amount, then it was for the scrap heap. Finally, they said they would think about it. Well, they “thought about it” for some six or seven weeks and I was heartily sick of having the thing cluttering up the workshop. But finally they rang and said, “fix it.” So I ordered the replacement transformer, which arrived in about a week, then set about putting it all back together. This wasn’t quite so bad; after all I’d been there before and learned some of the tricks and traps. Then came the moment of truth; would it work? Well, it did and quite well in fact – for a projection system. I gave it a grey scale and convergence routine and the hotel sent down their ute and another team of footballers to take it home. And I made one final check when it was back in the lounge, giving the convergence a final tweak. It appears that this adjustment is quite sensitive and the journey in the ute had upset it a little. So they paid the bill – just on $600 – along with some general comments about how expensive everything is these days. Well, it was a pretty expensive fuse. The rejuvenated National My next story is about a National TV set, model TC-2138, using an M14H chassis. These sets first appeared SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. 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As far as I could see, the winding was damaged internally. Not only was it a write-off but I now felt quite sure that it had originally been intermittent, leading to the pointless replacing of fuses. So it was back to Mitsubishi to determine the availability of a new transformer and its price. I was concerned about this latter point, feeling that it would be quite costly. And I was right. It was available but the cost, including freight, was just short of $400. Add in the labour costs – what had been done and what was yet to be done – and it was making a mess of $600. May 1995  79 SERVICEMAN’S LOG – CTD somewhere around 1987 and this was one of that vintage. It belongs to a family that are long-standing customers and I have serviced it for a couple of routine faults over the years. It gave pretty good service until about 18 months ago. Then it failed completely, due to some minor fault, and landed on my bench. A dismal performance As I say, the basic fault was minor, and I soon had it up and running. But it gave a pretty dismal performance. In simple terms, the picture tube had “had it”. It was so bad that I felt there were only two possible approaches: to try rejuvenating it or, if that failed, fit a new tube. I talked it over with the customer and suggested that since the tube was so sick, there was little to lose by trying rejuvenation. Granted, there are always risks with this approach. One is that it simply won’t work; that the tube will be no better off after treatment. The other is that the tube may suffer further damage and be a complete write off. But, either way, the final result is much the same; a new tube will have 80  Silicon Chip to be fitted, if not immediately, then in a few month’s time when the user can no longer tolerate it. I explained all this to the customer and he saw the wisdom of rejuvenation. So I fished out the rejuvenator and went ahead with the job. Basically, it consists of applying 700-800V between grid 1 and cathode and this should, hopefully, blast any accumu­ lated rubbish off the cathode (usually with a display of fire­works). Of course, this is a somewhat simplified explanation but it will suffice for this story. And it worked this time. Granted, the performance was short of “as-new” but it was still a vast improvement on what it had been. And when the customer and his wife saw the result they were highly delighted; they had obviously forgotten what a good pic­ ture looked like. But I had to add a final word of warning; I had no idea how long the improvement would last. I’ve known it to last for a couple of years but I’ve also seen it pack up after a few months. There is no way to tell and the customer accepted this. With this in mind, I told him that if – or, really, when – it failed again, to bring the set back; that I could probably do a good deal on a picture tube, adding that I had one on hand from a wrecked set. And I emphasised that his set was otherwise in good condition and worthy of a replacement tube. The set that fell And that brings me to part two of the story – a part which has its humorous side. This started about five years previously. It concerns another TC-2138 set, only about 12 month’s old at the time, which belonged to a local club. This was located in a convenient viewing position on a small shelf, a couple of metres above the floor, in one of the club’s lounges. Don’t ask me how it happened – lots of strange things happen in such establishments – but someone knock­ ed it off the shelf. And apparently it landed on a pretty hard surface which, combined with the 2-metre drop, didn’t do it any good. The first I knew about this was when one of the club’s staff walked into the shop carrying the set’s original cardboard carton Naturally, I expected a TV set requiring conventional service. He put the carton on the counter and said. “Can you fix this for us – it’s had a fall.” Even then I didn’t wake up; I imagined it had been simply knocked over or, at worst, taken a gentle tumble due to someone losing their grip while carrying it. Until I opened the carton, that is. And what a sight. It was just a mass of bits. These sets are housed in the usual chipboard cabinet and all four sides were now separate pieces, the glued joints having failed. The plastic back was broken, as was the mask around the tube. And when I took a closer look at the innards, I realised that the mother board was cracked right across. It was all I could do not to burst out laughing; surely he was­­­n ’t serious? It reminded me of all the stories I’d heard about amateur clock repairers, who finish up with a cardboard box full of bits on the local jeweller’s counter. I never did believe those stories but here was something that would top them all. I’m afraid I recoiled in disbelief and this was probably obvious. “You don’t seriously expect me to repair this?” It was the customer’s turn to express disbelief. “Aw, y’should be able to glue the cabinet back together.” Well, I had to agree that, yes, one could probably glue the pieces back together but when I tried to explain about the cracked board and other obvious damage, I realised I was battling against the wind. So I took the diplomatic step of saying, “leave it with me, I’ll have a look at it”. That at least gave me time to think. A hopeless case In fact, I did go through the motions of taking another look. Of course, it was hopeless. The motherboard was cracked from front to back, taking an erratic path around the horizontal output transformer, with a number of secondary cracks radiating from this area. But these were only the visible faults. Even assuming they could be repaired – or replaced – there was always the risk that more damage would come to light as one progressed. And what about the picture tube? Strangely enough, it was physically intact but what had such a fall done to its insides? Even if it still func­tioned electrically, there was a real risk that the shadow mask had been distorted and it would also be a write off. So I rang the club, contacted someone who seemed better able to appreciate the seriousness of the accident, and laid it on the line. There was no way that the set could be repaired and they would be well advised to cut their losses and buy a new set. This advice was accepted and I was thanked me for my trouble. Well, that was the end of that part of the story, except that I was left with a carton of broken bits. There was almost nothing left worth salvaging and I sent most of it off to the tip. But I hung on to the picture tube. It was intact, the scan coils were still fitted (also apparently intact), and shaking it failed to reveal any internal rattles. And so I tucked it away under the bench, hoping that I might get another TC-2138 through the shop so that I could test it. Well, it was over a year later but such a set did turn up. And as soon as I had it working, I fished out the spare tube and propped it up on the bench with its back facing the back of the set. It was the simplest possible operation. All the set’s leads were long enough to reach my tube without any fiddling and, in no time at all, I had the whole arrangement up and running. And not only did the tube and assembly work but everything was spot on and the picture bright and sparkling. I gave it a purity check and even this failed to reveal any problems. So, not only did I have a spare tube in good condition, but one complete with deflection coils and all adjustments spot on. It was, literally, a perfect plug-in replacement. So it went back into stock and I thought no more about is until my aforementioned customer turned up with his sick tube, and I went through the rejuvenation process. Had this not worked, then the tube from the junked set was a good candidate. But it did work and I thought the customer might as well get his money’s worth for a few months. In fact, it was some 18 months before I heard from the family again. Then the wife was on the phone one morning and opened the conversation with the rather matter-of-fact statement that the old TV set had given up the ghost at last. But this was only a prelude to the main reason for the call, which was to ask my advice about buying a new set. Probing a little deeper, I learned that “we stuck the old set down in the garage because we can’t use it any more”. Apparently, my suggestion about a replacement tube had been forgotten. I imme­diately enquired as to whether the set was still actually working and was assured that it was, but that the picture was now quite unwatchable. I then reminded the lady about my offer of a replacement tube and suggested that they bring the set in and let me look at it. At the same time, I pointed out that I could probably restore the set for a good deal less than the $700 or more that they would be looking at for a new set. The set returns And so the set duly landed back on my bench again. A quick check confirmed the situation. Yes, the set was still working and yes, the picture was crook – real crook. I pulled the old tube out, fitted the spare tube and con­nected the various cables. The whole operation took less that half an hour and resulted in a firstrate picture. And, since the scan coils were still as originally assembled and adjusted, no convergence adjustments were required. All I had to do was reset the grey scale, these adjustments having been juggled for best results after the original tube had been rejuvenated. This turned out to be perfectly routine and the end result was excellent. When the owners came in to view the result and collect the set, they were delighted because the performance was virtually that of a new set. But I was perfectly honest with them, pointing out that it was a secondhand tube with about 12 month’s use. I also explained how I had acquired it. How much did it all cost? I charged them $150; $75 for the tube and $75 labour, which I felt was reasonable. And the custom­ ers thought so too; they were more than happy with the whole transaction. So everybody was happy; they had a first-class working set for a modest outlay and I had made a few dollars on a tube I had scored and carefully SC stored for several years. May 1995  81