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. 'SLOG SERVIC When the ghost comes early In the spiritual sense, ghosts are not usually expected until after the main event; ie, after someone has departed this life. It's usually the same with TV ghosts. Normally displaced to the right, they are caused by signals which arrive after the main signal. I'm not all that well versed in spiritual ghosts but I have heard stories, from those who delve into such phenomena, about ghosts that appeared earlier than normal (ie, while the person was still alive). Admittedly, even the believers concede that this is very rare - compared with normal ghostly appearances, that is. OK, so my cynicism is showing. And I must admit that I tend to be trifle cynical also about early TV ghosts - leading ghosts, that is. Oh yes , I know they do happen; I've seen them but, like the spiritual early ghost, they are quite rare. So what causes a leading ghost? Until now, I have seen only one mechanism ; one where the TV signal finds its way directly into the tuner. Since the signal from the antenna takes a finite time to travel through the cable, it will arrive later than the signal picked u p directly by the tuner. And , the longer the antenna cable, the greater the ghost image displacement. The TV set will normally lock onto the stronger sync pulses so, if the signal from the antenna is the stronger (as it would be n9rmally), this signal will produce the "main" visual image and will be centred on the screen. The weaker image then becomes the ghost, whether it is leading or lagging. I once saw a classic example of a leading ghost. In TV's early days, a colleague had been involved in installing a large distribution system in a motel on Sydney's north shore, almost literally in the shadow of the transmission towers. The system had been run with coax 40 SILICON CHIP cable throughout, so it was a shock when all the sets produced leading ghosts. The cause was eventually traced to the sets' physical layout. The tuners were mounted at the front of the chassis, with about 30cm of soon ribbon running to the antenna terminals at the rear. And the ribbon was the culprit; in the shock area, it was picking up a substantial signal. Shielded cable cured the problem. Even rarer than the leading ghost is a ghost generated by the TV set itself. I am less familiar with these but a colleague has encountered a few. The exact mechanism is unclear but most TETIA TV TIP Philips GR100 chassis Symptom: no sound. Picture is perfect c:1.nd all other functions work correctly but there is no response from the volume control. Cure: this chassis features a "hotel" mode which allows the hotelier to silence noisy sets in rooms occupied by inconsiderate guests. The function can sometimes be triggered unintentionally by spikes on the mains. The cure is easy. Simply select Channel 38 with the remote control, then press "Store" and "Control +" together. TETIA TV Tip is supplied by the Tasmanian branch of the Electronic Technician's Institute of Australia. Contact Jim Lawler, 16 Adina St, Geilston Bay, 7015. are caused by a fault in the IF strip. The suggestion is that it is due to some kind of frequency dependent phase shift, whereby the higher frequency video signals (ie, the fine details of the image) reach the video detector before the lower frequency video signals and sync pulses. Another cause experienced by this colleague was a faulty luminance delay line, in an early colour set. The delay line was an inductor about 12cm long and 9mm diameter, over which was a metal strip, forming one plate of a distributed capacitor. The fault was due to a faulty chassis connection to this metal strip. And what about an internally generated leading ghost? Well, nobody seems to have heard of that one. Until now. The ghostly Mitsubishi · The set involved was a an AWA Mitsubishi model SC6601, sold by a dealer colleague about nine months previously and thus still under warranty. The owner rang me first, complaining that the set had developed bad ghosting. And it was clear that he firmly believed that the set was at fault. Naturally, I was sceptical, not only in the general sense but because of the customer's location. There was a multi-level department store being erected at a nearby shopping centre, with the usual assortment of tall cranes reaching skywards. This had prompted a swag of complaints, both to me and as letters to the local newspaper, about interference to TV reception in the area. The construction company, while sympathetic, could do little to help. But they did advise that the cranes would probably be gone in a few weeks and that, hopefully, this would ease the problem. So, on this basis, I advised the customer to wait and see what happened. If the problem persisted, I would get one of my antenna and I are pretty adept at such jobs, so together we manhandled it into his van and delivered it to the workshop. Initial checks lI Q] \ t 1 ! ONC~ SAW A.. C.l.A4S"SI C. eJ<AM'Pl-E OF ~ C-£ADIN6 GHOST":., installation colleagues to have a look at the setup. The next thing I heard, about a fortnight later, was from the dealer. Apparently the owner was becoming impatient and had contacted him about the problem. Fortunately, the dealer was about to make a delivery in that area, so he took the opportunity to call. And he was smart enough to take another small set with him. This check was most revealing, because the dealer's set produced a virtually ghost-free picture. And that meant that it was an internally generated ghost, which put an entirely different complexion on things. My dealer colleague suggested I visit the customer's home, check his findings and perhaps fix it on the spot. "No way", I replied. "No way am I going to tackle an internal ghost problem in the customer's home. It's going to be hard enough in the workshop. We'll have to bring it in". I used the word "we" advisedly because I knew why my colleague had suggested I go to the customer's home. This is a 65cm set although, in most cases, I can usually handle sets of this size alone, albeit with a bit of puff and grunt. But not this one. It was housed in an enormous cabinet; the kind that normally needs a couple of furniture removalists to shift it. Well, almost. In fact, my colleague Two things had emerged from the visit to the customer's home. One was his discovery that the problem was intermittent - which didn't cheer me up at all. The other was that the two images were displaced by about 1520mm and that they were of almost equal intensity. I didn't even try to rationalise this last effect at this stage; time enough when I had it on the bench. So I set it up and fed in a signal from the pattern generator, choosing a simple one consisting of a circle, a cross and a border. It has no cross hatch and is ideal for observing ghosts and also for centring the picture. Now, with a steady pattern, I realised that one signal was slightly more intense than the other and had assumed the main signal position at centre screen. But the weaker image was to the left of the main image; in other words, a leading ghost. This was a bit of a shock initially but, on reflection, I decided that it was probably of more academic interest than anything else. If the previously expounded theory was to be believed, it simply meant that the high video frequencies were arriving ahead of the sync pulses. This might mean something to the set's designer but it meant little to me in practical terms. In fact, I had very little to go on, apart from the above secondhand experiences. I didn't even have a manual for the set and so I phoned AWA and was assured that one would be despatched immediately. And they were as good as their word - except that, somehow, the circuit diagram had been omitted. It took another phone call to get that. Unfortunately, I found that it left a lot to the imagination but more of that later. Three suspects By now I had mentally designated three s-qspect areas: the tuner, the IF strip and the luminance delay line. I put the delay line at the bottom of the list. According to my colleague, the displacement he encountered due to this cause was minimal and was more akin to a bad case of ringing than the marked displacement that I was observing. DECEMBER1991 41 SERVICEMAN'S LOG - CTD After that, I tended to favour the IF strip but decided to eliminate the tuner first, since it was easy to do. I simply reset the generator to the video IF (36.875MHz) and injected this signal into the IF pack. The result was totally conclusive; the ghost was still there and the tuner was cleared. Unfortunately, there were a couple of problems with the IF strip. The circuit showed this simply as a box, with 11 terminals, marked VIF-Pack. And the chassis itself was just as coy; the pack was a metal box, about 73 x 50 x 25mm, with 11 terminals. And it was tucked in•between two vertical boards on the lefthand side of the main board. Getting it out was more tedious than difficult but it was eventually done. When I opened the box I found it to be a typical IF system; a transistor, a SAW filter, an IC and a few discrete components, all on a small board. The intermittent nature of the fault (which I had confirmed) suggested a possible dry joint, and this was my line of attack. I went over the board with a glass and found not one but three obvious dry joints, which I repaired. I then put everything back together, refitted the box in the set, rubbed my hands with satisfaction (/) . R 42 The right track I did this and found myself talking to a technician who was obviously familiar with the problem. As far as he was concerned, I was right; the problem was in the IF strip. Well, that was some encouragement. Having checked what I had already done, he went on to suggest the joints of several other components. One of these was the SAW filter and another a small trim pot (the AGC preset). In addition, there were three other small components which, without a circuit, I couldn't identify. These were mounted on the copper side of the board and were probably small capacitors. I would have liked to have discussed the theory of the problem in detail but there was little more that he could tell me. So I pulled the pack out again and checked these components. The trimpot connections were above suspicion but, in any case, I doubted whether it could be responsible for this fault. The joints of the other three small components were equally above suspicion. That left the SAW filter. The SAW filter has five connections, two being to the chassis. And, having been alerted, a more de tailed check did suggest that some of them were rather "iffy". I resoldered them all, checked the rest of the board again, and refitted the pack. I put the set through another series of exhaustive bench tests and it performed faultlessly. After about a week, I concluded that the ghost had been finally laid and so the set was returned to the customer. A recent • check, two month's later, revealed that all oooAN'D INOUl-'D '<OIJ 'B~Uf:\JE. \ , ; 11.\G:' was well. However, the phrase ONLY 'PAN\At:>~ WP.S ~ T\N'< C.\·\\? OF\= mE: CA'e>\Nf;"f"ooo ~!!{p (fi; and switched on. You beaut! - no ghost. I let it run for several days, switching it off and on occasionally, and it didn't miss a beat. But then I left it off for a couple days and, when I switched it on again, there was the ghost - but for about 30 seconds only. I ran it for several more days, switching it on and off, thumping and otherwise abusing it. No ghost. I left it off for a couple of days and tried again. And again, the ghost appeared for 30 seconds at switch on but nothing more. At this point, I decided that, rather than waste more time, it would be better to fit a new IF pack, seeing that the set was under warranty. So I rang the company's spare parts department to order a replacement pack. They were out of stock but expected new stocks in about two weeks. Well, that was OK, the dealer had loaned the customer another set and a couple more weeks shouldn't matter. But the two weeks dragged on into four and when I rang I was told that there had been a delay in supplies from Japan and that it could be several more weeks - or even longer before stocks arrived. The company was both apologetic and helpful, suggesting that, if the worst came to the worst, they would "borrow" a pack from another set. But they suggested that I first talk to the service department, in case there was still a chance of repairing the existing unit. . .,, SILICO N CHIP "returned to the customer" in the previous paragraph has a deeper meaning than its simplicity implies. It was a near disaster. I've already mentioned the bulk of this set and the need to have two people to move it. Well, when it came time to return it, the dealer who had helped me bring it in could not immediately spare the time to help again. I explained the situation to the owner who was quite happy to help at his end, so I shanghaied a colleague into helping at my end. The snag was, the owner had his own ideas on carrying the set. He insisted on going first - which was OK by me - but also on walking forwards, supporting the set behind his back. Years of experience have taught me that this is a risky practice; it is simply not possible to get as secure a grip this way as it is when facing the load. Granted, one needs to make sure that there is a clear path and to check out steps, doorways and other obstructions but, on balance, facing the load is the safest way. I suggested I go first but this was ruled out. So we started up the concrete path to the one step leading to the house. The path was smooth and level but the edges had been finished with a raised roll, about 75mm high. All went well until he reached the step at which point, for some unexplained reason, he stumbled. What happened next was all over in milliseconds. He lost his grip on the left side of the set - the front - so the face of the picture tube was heading for the raised edge of the path. I suppose it was pure instinct which made me do what I did, because there was no time to think. I lifted the right hand side of the set with all the force my arm could muster. And it worked; I rolled the set through 180° and also pushed it beyond the path. It landed on the top of the cabinet, legs ·in the air, on the adjacent grass. And would you believe it; the only damage was a tiny chip off the cabinet veneer at one corner. There was no internal damage. But it was too close to an oops for my liking. A genuine oops And finally, here's a genuine oops. The first part of this story occurred long before I came on the scene but this is how I pieced it together. It concerns an up-market stereo amplifier, a Technics model SU-V460 made by Matsushita. This amplifier is rated at up to BOW per channel and has all the usual bells and whistles dear to the heart of the audiophile at a price somewhere between $700 and $800. It had been sold by my dealer colleague only about 18 months previously and, by all accounts, the customer was very happy with it. Or at least he was until the night of the party. The details of the party are a bit vague - nobody was saying much, even if they could remember, which is probably understandable in the circumstances. However, there was a broad hint that the party was what one might term an unofficial one - that the owner and his wife were away and "while the cat's away, the mice will play" the "mice" being the teenage offspring, mates and girlfriends. Anyway, someone managed to overturn a glass of drink on top of the amplifier. After which it didn't go. And so the owner took it back to my dealer friend, sheepishly confessed that something had been spilt into it, and asked what could be done about it. My friend removed the cover, took one sniff at the inside, and nominated Coca Cola. He then suggested that he should pass it over to me, as an authorised Panasonic Service Centre. But no; the owner insisted that it be returned directly to Panasonic, to ensure that the job "was done properly". (Bit of a blow to my ego, that). And so this was done. But it received short shrift at Panasonic. It came back with a brief note saying that the unit was not worth repairing; it would be cheaper to buy a new one. Naturally, the owner wasn't very happy but at least he accepted the diagnosis. And, in retrospect, I'm thankful that it was Panasonic that delivered the verdict, rather than myself. I wonder whether he would have taken my word as readily as he did their's. And that softened the blow to my ego somewhat. It was at this point that I first learned of these happenings, mainly because my dealer friend was stuck with the relic, and was about to send it to the tip, when it occurred to him that it might be of some use to me. He was TV TEST EQUIPMENT (AUSTRALIAN MADE) SHORTED TURNS TESTER Built-in meter to check EHT transformers including split diode type, yokes and drive transformers. $78.00 + $3.00 p&p * * * * * * * * * DEGAUSSING WAND Strong magnetic field , larger than usual coil with multicore centre. Double insulated for your safety. Also fitted with momentary on/off switch. 240V AC 2.2 amps. Just about as important as having a soldering iron in your toolbox! $75.00 + $10.00 p&p * * * * * * * * * HIGH-VOLTAGE PROBE Built-in meter reads positive or negative voltages from 0-50kV. For checking EHT and focus as well as any other hi-tension voltages. $98.00 + $5.00 p&p LOW-VOLTAGE PROBE Ideal for checking microwave ovens & TVs. The ranges are 0-5kV ·negative & 0-10kV positive. Double insulated for safety . $84.00 + $5.00 p&p * * * * * * * * * REMOTE CONTROL TESTER (INFRARED OR ULTRASONIC) Designed to test inlrared or ultrasonic control units. With the extension lead you can also test inlrared units which cannot be placed in front of the testing unit. Requires a 9V battery. Output is via a LED and piezo speaker. $84.00 ~ $4.00 p&p . ·.· .· ·, ♦', >;:.., / · ~- TUNER REPAIRS ./..r. ~ . From $19 exchange ~ . - plus p&p ...._ ~ - ✓ P,~.~~--- Cheque, Money Order, Visa Card Bankcard or Mastercard 216 Canterbury Road, Revesby, NSW 2212. "'2:r (02) 774 1154 .·-...!!!!(02) 774 1154 DECEMBER 1991 43 SERVICEMAN'S LOG - CTD Fig.1: general layout of the SU-V460 amplifier, showing the output stage heatsink, with the amplifier output IC (SV13205) on the front of it. It was in this area that the Coca Cola landed. aware that I had been thinking about such a piece of gear and that I might be able to salvage if I could afford to put some time into it. The idea intrigued me too. Without for one moment questioning Panasonic's diagnosis, I felt there was a fair chance that it might be possible to restore the amplifier for a modest amount, in my own time. And I already had a manual for it. And so it finished up in the workshop. I pulled the covers off and began assessing the damage. It was a mixed bag; there was not much to be seen at first glance but closer inspection soon revealed the details. This unit has a large main board (about 300 x 220mm) sitting on the bottom of the cabinet. Among other things, it carries the driver stages and the output IC for the power amplifiers. This output IC is mounted on a large finned heatsink which in turn is mounted above a central cut-out area measuring about 200 x 90mm. And it was on this heatsink and the surrounding board that most of the Coke appeared to have landed. The preamplifier and frequency control stages, along with the switches and other controls, are on a separate front panel board. They appeared to have escaped serious contamination. Vaporised links The output IC - IC501, SV13205 connects to 18 terminal pads on the board, along one edge of the cutout area. And this was where I first found obvious - and quite startling - dam44 SILICON CHIP age. Four of these terminal pads, 3, 4, 5 & 10, are connected to other parts of the board via short wire links. In fact, pins 4 & 5 are connected to 45V rails, while pin 10 connects to a 15V rail. Or, more correctly, they should have been so connected. In fact, some links no longer existed; they had been completely vaporised - a dramatic indication of just how violent the reaction had been. There were other links nearby which had also suffered, although not so drastically; these had simply melted, leaving most the wire in place. From here, I turned my attention to a group of 16 transistors on the main board - Q451 to Q465 - which make up the amplifier input and driver stages. There had been some violent reactions here also. Some of the transistors had been literally blown to pieces; all that was left were the legs with a few scraps of black encapsulation clinging to them. Of those physically intact, an insitu meter test indicated that most were faulty, while the others were doubtful; which meant that they would all have to be replaced. And, iri the same area, there were a number ofresistors which had obviously been badly overloaded. At this point I decided to make a rough estimate as to the cost ofreplacing those components that were obviously faulty. A quick check with Panasonic revealed that the output IC (IC501) would cost well over $100. Add to that the 16 transistors, sundry resistors known to be damaged, plus allowance for components not yet checked, and there wouldn't be much change out of $200. Well, OK, an $800 amplifier for $200 (plus the labour ofreplacing the faulty bits) doesn't sound such a bad proposition. But was that all that was involved? On closer inspection, I real 7 ised that it was not. Between the 18 pads and tracks feeding the output IC, I discovered considerable carbonising of the board. Now, it is usually possible to correct this situation by gouging out the charred material and is always worth a try where it is only minor and there is little other expense involved. As I say, it usually works; but not always. But this situation was quite different. The charring was extensive and the. space between tracks quite limited. And it would be impossible to know whether the work had been successful until I had bought and fitted some $200 worth of components. And this was only on the basis of the known faulty components. There would almost certainly be more and, in particular, I was worried about those on the front panel board. These included three ICs, various switches and potentiometers, plus a swag of minor components, any of which could have been damaged in one way or another. This would add to the cost but, even if this was only minor, there would also be the time needed to track them down, which could be quite tricky. And if one of them was intermittent, it could take a considerable amount of time to track down. The upshot of all this was that I had to shake my head and push the thing aside. What had initially looked like an attractive idea was simply not a practical proposition. I have recounted this story for a couple of reasons. The most obvious one, of course, is to emphasise that electronic devices and beverages do not mix. Such devices should not be located where people - and particularly inebriated party guests - are tempted to use them as a table. The other point is to vindicate the original diagnosis by Panasonic. Customers often accuse service organisations of taking the easy, and more profitable, course of writing off a device, when a repair really is economically possible. Well, perhaps it does happen. But not with reputable organisations. SC