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Sing it again Sam(sung) My main story this month concerns a brand of set which is relatively new to the Australian market. So, as well as discussing specific technical problems, we will take the opportunity to present some general background to it. The brand involved is Samsung, a Korean based company represented in Australia by Samsung Australia Pty Ltd (10/16 South St, Rydalmere, NSW 2116). As I said, this is a relatively new brand on the Australian market, having come to local prominence only in the last 12 months or so. And quite naturally, customers are tempted to ask just what kind of an organisation is behind this brand name. Fair enough. Well, for starters, while the brand name is new, the products have been around for a good deal longer. Most servicemen will recognise them as having been previously marketed under the 58 SILICON CHIP "Princess" and "Palsonic" labels. They are a large organisation. As well as TV sets, they also manufacture video recorders, audio equipment (including CD players), microwave ovens and computers. Their products are well established in the United States and they have manufacturing interests in other countries as well. Indeed, the brand has been well known in New Zealand for several years, where Samsung has a small assembly plant. They also have a very large manufacturing plant in Wales producing TV sets, video recorders and microwave ovens for the British market. So Samsung is no pip-squeak, fly- by-night organisation; it is just that we have only recently become aware of it in Australia. Samsung service My association with the brand began when one of the local dealers, for whom I do warranty and other service work, decided to market these sets. As part of the deal, he was required to organise warranty service so he suggested that I might be interested. Well, I am always interested in more work. At a technical level, my experience with the Princess and Palsonic models over the years had indicated that they were fairly conventional sets. In fact, they were no more difficult to service than most other brands. More to the point was whether Samsung and I could reach a satisfactory agreement. As many of my colleagues will testify, warranty service has not always been the happiest arrangement in the past, at least with some companies. What has seemed like a reasonable proposition in theory has not necessarily proved so in practice. Anyway, the dealer passed my name on to Samsung and they in turn approached me. Alerted by some of my previous experience with warranty work, I laid it on the line that I would need certain firm undertakings before committing myself. First, I needed to be assured of the ready availabilty of properly prepared manuals. A lack of manuals, or manuals that are not well written, can be more than simply frustrating; it can be very expensive, particularly with new or unfamiliar models. As a result, what should have been a modest profit can become a substantial loss. The next question is technical backup. While it is unreasonable to expect a company technician to have an immediate answer for every "funny" that turns up in the field, there is nothing more frustrating than talking to someone who obviously knows less about a piece of equipment than you do. So could I bank on adequate help when I needed it? Finally, there is the question of spare parts. Of all the frustrations we face, lack of spare parts is one of the most serious. It is often a big enough problem to diagnose a tricky fault without then facing the situation that the vital part involved is "on back order". Such situations can mean a delay of weeks or even months, while the customer fumes and the servicem~n becomes the meat in the sandwich. And it doesn't help that some customers refuse to accept that this is the true situation, preferring to believe that it is the serviceman's own laziness or incompetence (which, I regret to say, is true in some cases) that is the cause of the problem. Anyway, those were the major points I raised. And the company didn't quibble; they were eager to assure me that all those conditions could be met and so far they have been as good as their word. I only hope that they can keep it that way. But it wasn't a one-way deal. They wanted some assurances and background from me. In particular, they wanted to know how long I had been in the industry and asked questions about my workshop facilities and test equipment. Since I've been in the game for more years than I care to think about, and since my shop is as well equipped as anyone's, I didn't have any problem meeting their requirements. And so an agreement was reached which means that I am now an authorised Samsung service centre. Basic models All this happened several months ago and since then I have had the opportunity to come to grips with these sets at a practical servicing level. The range includes 34, 40, 45 and 48cm models and all appear to be designed around a fairly basic chassis, with only minor variations. There is also a portable set, designed for both 240V AC and 1 ZV DC operation. It uses similar basic circuitry. The most recent addition is a 63cm model but I have no data on it yet. The basic chassis is the P/50F and the sets based on it, which I have encountered so far, are the CB515F and CB515Z, both 45cm models. The "F" version uses an 8-channel pushbutton tuner while the "Z" version is fitted with remote control. The "F" version is a very popular model and my dealer friend has sold a couple of hundred so far, many to local motels. Apparently, motel owners regard the "F" version as ideal - it's a simple set, the size is right, and the price is attractive. One motel alone recently purchased 29 of these sets. In fact, I've opened a special file on these. Since they all came on line at the same time and are operating in the same environment, they should provide a lot of valuable service data. The nitty gritty Y~'P, NOION~ COMPLAIN-,- ABO OUR -rv S Now let's get to the technical nitty gritty. What I am about to relate covers virtually the same fault in all cases, producing the same major symptom but with varying secondary symptoms if neglected. The major symptom is a bright vertical line in the centre of the screen. This is an unusual symptom in that it obviously indicates a deflection failure but no accompanying EHT failure. An extreme side effect of this symptom, if it is allowed to continue, is a burnt board. This happened to a motel set on one occasion and left a hole big enough to pass a 5c piece. Digressing for a moment, this raises another matter which is peculiar to the motel scene. Faults in motel TV sets can often go unJANUARY 1990 59 SERVICEMAN'S LOG -CTD noticed for days, or even weeks. Most guests stay only one night and, unless they are TV addicts or wish to catch a particular program, a faulty set tends to be shrugged off as bad luck. By the morning it is forgotten and no-one is any the wiser. A further complication arises when the fault is intermittent, as it often is in this case. It may escape routine inspection or, worse still, may be deliberately left in service on the basis that it works for most of the time anyway, so why worry. I am now trying to instill some sense of responsibility into those concerned by emphasising the need to take a set out of service immediately this fault - or any fault - is observed, to avoid the risk of further damage. As already stated, the problem involves the horizontal deflection circuit, as distinct from the horizontal output stage. More precisely, it involves the area around inductor 1401 which is in series with 1408/ C414, side pin-cushion coil T402 and the horizontal deflection coils (see Fig.1). The problem is basically one of quality control, because it boils down to a series of faulty soldered joints. And note that I said "faulty" rather than "dry", because my im. pression is one of fractured joints, such as occurs when the two components are allowed to move before the solder has properly set. It is not an unusual fault and some early local production runs produced boards which were literally riddled with such faults. They were so well known that we treated them as routine. To be fair to Samsung, they are aware of the problem and have taken steps to correct it. In the meantime, those sets already in the field have to be dealt with. And again, to their credit, they didn't hesitate over the burnt board. I returned the set to them and they simply replaced it with a new set. The main offender is the joint at the" hot" end of 1401. If allowed to persist, this will destroy R413 because all the horizontal current 60 SILICON CHIP HORIZONTAL DEFLECTION _ ___._TO COLLECTOR OF 0404 R430 150{) C454 1 R~i3 L401 .,. TO HORIZONTAL OUTPUT TRANSFORMER Fig.1: this simplified diagram shows where the bad solder joints can occur in the Samsung CB515F. The immediate symptom is intermittent loss of horizontal deflection but damage to the board and to components can also occur if the sets are left in service. involved must now flow through it. Another version of the fault involves C414, which may be faulty at either end. In either case, prolonged use of the set in the fault condition can result in a burnt board in this area. Other secondary effects encountered so far include destruction of the horizontal output transistor (Q404), R423 or R420 (both rn ½ W safety resistors), and diode DHl or its associated resistor, RHl. The important point to note here is that the set may be presented to the serviceman as completely dead, due to one of the abovementioned secondary failures, and may appear to be fixed when the faulty component is replaced. In fact, the real cause - the faulty joints may simply be lying dormant, ready to strike again. So be warned. From southern shores Talking about vertical lines on the screen, here 's something from our southern sub-continent, as told by J.L. I thought I had seen just about every kind of TV fault there is but one showed up recently that really had me guessing. The set was a Sharp CX4846 and the "funny fault" was not immediately apparent. It came in with a report that the screen was very bright, with retrace lines, and that it sometimes switched itself off. No mention was made of the fact that there was no picture but that was the case. The excessive brightness was not all that difficult to solve. Somebody had been inside the set and had turned the screen (G2) control to full on. The excessive beam current under these conditions was close to the shut-down level for the power supply, which explained the occasional switching off. The final evidence of unqualified intrusion was that six of the 10 screws securing the cabinet back were missing and the remaining four were all loose by several turns. Mr Nobody It's funny, though. Quizzing the owner produced the answer "Oh, no! Nobody's touched the set". That Mr Nobody has a lot to answer for. Turning the screen control down to about half way produced a typical snowy screen and the retrace lines disappeared. It was at this point that the "funny" appeared. Right down the full height of the screen, about one third of the way from the left-hand side, there was a dense black band a bout 35mm wide. There was no sign of a picture, with each of the 10 channel buttons producing identical snowy screens. It transpired that Mr Nobody had not only fiddled the G2 control but also the channel selectors. My next job was to retune the various channels. The self-search tuning in this set was very slow and it seemed to take forever to get the first channel on screen. When I did, I could see the fault in all its final confusing glory. The black band had grown into a 75mm wide strip that had every sign of being the horizontal blanking bar. I had seen this in other sets when I had floated the horizontal scan but I had never seen it rock steady in an otherwise perfect picture. ("Floating" involves disconnecting the horizontal sync pulse and then adjusting the hold control until the picture "floats"; ie, almost stationary or drifting slowly from side to side. The trick is a useful one to This photograph shows the displaced image on the faulty Sharp CX4846. The black vertical band is the horizontal blanking period and the image at the extreme left belongs at the extreme right. determine if horizontal instability is caused by a bad horizontal oscillator or by faulty sync pulses). A Philips PM5544 test pattern from SBS showed just the extreme right hand side of the test pattern, on the left hand edge of the screen. After the right hand castellations, there was a narrow band of grey down the picture, then the solid black bar began. Right down the middle of the bar was a narrow green line, then more black bar before another grey strip, then the left hand castellations at about a third of the way across the screen. The rest of the test pattern was free of horizontal or vertical non-linearity although about a third of the circle was lost. As a matter of interest, the green line was the chroma burst. The sync pulses were buried in the first half of the black band and, because they are "blacker than black", could not be seen on this picture. Fixing it So that was the nature of the fault and it was now up to me to find out what it was and fix it. I mentioned earlier that someone had turned up the G2 control. My first thought was that they had also meddled with one of the horizontal presets and so messed up the horizontal timing. But there were only two horizontal presets, a horizontal frequency and a horizontal shift, and neither of these had been touched. Nor would any adjustment correct the fault. This seemed to be a case of "false line lock", a condition that I have heard of but never seen. It occurs when something either delays or advances the triggering of the horizontal oscillator. If the trigger was 32 microseconds late (or early), the blanking bar would be near the centre of the screen. In this case the triggering was probably about 42µs late (or about 22µs early). Horizontal oscillators are invariably of the "flywheel" kind, designed to prevent noise accompanying individual sync pulses from causing random triggering and "shimmering" in the horizontal plane. These oscillators usually have an LC circuit that can be adjusted to run at approximately the horizontal line frequency. This is then phase locked by a discriminator circuit that compares the timing of the sync pulse with a pulse from the flyback transformer. The whole system is given a relatively long time constant to provide the flywheel effect. Until recently most of the components needed to run the horizontal department were discrete and the horizontal oscillator coil was easy to find and adjust. But not any more! In the Sharp CX4846, the entire horizontal stage is contained in a single integrated circuit, an IX 0602CE, and there is nothing that even looks like a conventional coil type oscillator. Even the hold and horizontal shift presets are subminiature pots about 6mm in diameter! Even so, unless the designers have come up with some new type of sync pulse horizontal drive, the oscillator still needs a sync pulse and a horizontal output reference pulse. These pulses have to be supplied from other parts of the set and fed into the oscillator chip. So I tried to find them with the scope. This is where I encountered the first major hurdle. This set seems to be an offshoot from VCR technology. The entire circuit board is only about 25cm square and is tightly packed with subminiature and ultra-miniature components. In addition, some of the circuit board tracks are hair-thin and are often completely covered by the printed overlay. This made it almost impossible to trace the tracks and I found that I simply couldn't find the sections I needed without the full service manual. So I advised the customer that his repair was going to take some time and sent away for the needed publication. When the manual arrived, I lost no time in looking up the horizontal oscillator section of the circuit diagram. What I saw made me shudder. There is hardly any part of the oscillator that is outside the big integrated circuit mentioned earlier. Not only that, but many other functions are also enclosed within the chip. There's a complete audio stage, including IF and output; a video IF amplifier, synchronous detector and video amplifier; a sync separator, vertical oscillator, V and H blanking amplifiers, burst gate amplifier and detector; AFC and AGC detectors; and, of course, the horizontal oscillator I was trying to analyse. With so much going on inside the chip, I would not be surprised to find that it was the cause of my trouble. But by the same reckoning, I would expect to see some other JANUARY 1990 61 t l 0 ~ l now had to consider the possibility that it was faulty. It was time to get out the freezer spray. With the set warmed up and the fault apparent, I went over the IC and surrounding components with the spray. Nothing happened. I widened the area of interest, spraying the other chips , various resistors, capacitors and transistors right up to the horizontal output transistor. Still nothing happened. The fault remained and stayed rock steady. Then, after a few days of this delayed onset, the fault decided to revert to its earlier "instant on" pattern. By this time I'd had enough and elected to change the chip. The problem licked I. 1-\i:\"D 1<.a:::.i;.NT"L..'-< INVE-S'1e.D IN A VACUUM DE:SOL-DE:.'RI NG s·n::~,TIONoo• symptoms if it was indeed the chip that was faulty. I had no wish to replace an expensive 28-pin IC until I was absolutely certain that it was at fault. I decided that, before I went that far, I would check surrounding components that might have some connection with the trouble. These components included two electrolytic capacitors attached to two timing circuits inside the chip the phase detector on the horizontal oscillator and the coincidence detector on the horizontal oscillator timing switch. Both of these are 0.47µF 16V units and these small value electros are notoriously unreliable. They were removed and replaced with new capacitors but to no avail. The picture continued to show the horizontal blanking bar - until next morning. At the next switch-on the picture was perfect, without a sign of the earlier trouble. I tried various thump and bump routines but nothing happened for half an hour or more. Then, the picture started to shiver, as if it was about to lose horizontal hold. Finally, the whole picture shifted sideways and locked into the fault condition. 62 SILICON CHIP Two aspects of this reversion to the fault condition led me to think that it might be the chip that was faulty after all. One was the warming up time taken before the fault showed. Admittedly, until now, the fault had been present from cold but I had changed a few components and I had been poking around in the circuitry. This could have led to a slowing down of the onset of the fault. The second indication was that the fault did not snap on but wriggled and shivered for a minute or so before settling down. I still wasn't keen to change the big chip but I TETIA TV TIP GEC 2213A Symptom: No sound or picture. All fuses are OK and there is 320V on the collector of the chopper transistor, TR502. Cure: R503 (22k0) open circuit. This resistor supplies 1 2V to run the chopper control IC and disipates 4.9 watts . The original 5W resistor is rather underrated and a 1 OW replacement will ensure more reliable operation. My usual suppliers had no IX 0602CE in stock and had to place it on back order. I had a week off from worrying about the Sharp before the chip arrived. I had recently invested in a vacuum desoldering station and its value was really shown in this job. In fact, I had the old chip out in two minutes, without the usual struggle and risk of damage to the printed tracks. The new chip went in just as easily and at first switch-on there was no sign of the fault. Repeated trials over the next few days seemed to indicate that the fault was gone. A week later and I was sufficiently convinced to return the set to its owner. There have been no further complaints. When you say it quickly, this job has not been all that unusual. Right from the start the integrated circuit was suspect. But its replacement cost of some $30 plus the difficulty of de-soldering the 28 pins was enough to encourage me to try everything else first. This has been one of those jobs where one wastes considerable time first up but recovers the wastage next time a similar fault appears. And if telling the story here helps you to save some time when you see this fault, then the time has not been wasted after all. Thanks J.L. I think that's enough to keep our readers on their toes for this month. Cheers for now. ~