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SERVICEMAN'S LOG It took longer but it cost less Security systems aren’t my normal run-ofthe-mill fare and one that I recently encountered caused a few hassles. My other big hassle this month concerned a manual with a wiring error. And from New Zealand I have a story about an 11kV power line which tangled with the 230V supply. My first story this month is about time-lapse video recorder security systems. Rather than scan continuously at the usual 25 frames per second, they take a single picture every few seconds. These expensive high-technology systems are fast becoming superseded. They are being replaced by lower cost PIR (passive infrared detectors) and add-on security kits for ordinary video recorders, which are activated only when movement is detected. Most older time-lapse systems cost around $2000 and are designed to run continuously, recording up to 720 hours on one tape. Obviously, they require regular maintenance and most are supplied with clocks to remind busy security control rooms that it is time for a service every 1000 hours. Nevertheless, they inevitably don’t bother with this until something actually fails. An urgent job So it happened recently that a local security company brought in a Sanyo TLS-1000P recorder, complaining that it would­n’t play and that it chewed tapes. The security officer who dropped it in said that the job was urgent but the manager of the company wanted a quote first. “Well, it’s either urgent or you want a quote; which is it?”, I replied. He called the manager, a man named Bob, on his mobile phone. “Look”, Bob said, “the machine 28  Silicon Chip is about 10 years old” (he was right about that). “Is it worth fixing and if so, how much?” He told me that he really didn’t want to go to the expense of re­placing it and in the end we agreed to go ahead with the repair, up to a limit of $300. Because the job was urgent, I attacked it straight away. First, I noticed that the hour meter on the front panel was showing 10,000 hours or full scale deflection. This timer uses a mercury column inside a 3AG fuse which is permanently connected to the switch­ed 12V rail. I have absolutely no idea how it works or how to reset it; perhaps it has to be plugged in upside down? What I do know is that it isn’t available as a spare part any more. Anyway, after all this time, it was due for a major service in anyone’s language. The second thing I noticed was that it didn’t want to accept tapes. I removed the covers and saw the major problem immediately – the capstan motor belt to the reel idler had bro- Sets Covered This Month • Sanyo TLS-1000P time-lapse video recorder • • Sharp V1 Stereo A-V System Sanyo Model C14ZA25 colour TV set ken and all the other belts looked in a sorry state. A new belt kit was fitted and this time the tape went in straight away and all the main functions appeared to work OK. However, when I tried to eject the tape, it didn’t want to. Each time the recorder is switched off at the power point and switched back on, the letter “P” appears to indicate a power failure. The recorder then has to be reset. When I did this, the tape ejected properly. I then tested it a number of times and it worked faultlessly. Having solved the main problem, I cleaned the rest of the machine and checked all the items listed in the maintenance table. I replaced a few suspect or worn parts but despite its high usage, it really wasn’t in bad nick. Noisy mode select switch When I had finished, I put the tape in again to test it and once again the set seemed unsure as to whether to accept it or not. I felt sure this was due to a noisy mode select switch and gave it a good squirt of switch lubricant. After that, it worked like a Swiss watch. The switch obviously had to be replaced and so I ordered a new one from Sanyo, only to be told that it was no longer avail­able – after all, the set was manufactured in 1989! As the mechanism is similar to the VHR3500 and VHR3700 VCRs, I wondered whether the part number had changed but a quick check soon showed it hadn’t. Fortunately, I decided to look through my local parts supplier’s catalog and noticed from the pictures that he had genuine new ones in stock and so I ordered one. It arrived the next day, just as the old one was playing up again. Anyway, I managed to get a tape in so that I could align the switch to its notch position. I then turned the machine off before unscrewing and unsolder- new switch and had to check the part number from the catalog. It was while the catalog was opened that I noticed a switch that looked exact­ly the same on the adjacent page but with an entirely different part number. It was this new switch that finally put the problem to bed. Bob wasn’t too happy with how long all this had taken but calmed down when he found out that the bill was a good deal less than he had been prepared to pay. The Sharp stereo A-V system ing the switch terminals from the PC board. The new one was just as easy to fit and no further adjustment was necessary. Unfortunately, when I finally reapplied power, it still wouldn’t eject. I checked all the other functions which were fine but, in the eject mode, the loading motor turned until the front (or “flont”, as the manual spells it) loading gear engaged with the capstan motor. And that’s as far as it got – the motor would­n’t turn at all. It was then I noticed that the surface-mounted fish-oil capacitors on the stator board were leaking. Aha! These looked like likely suspects. After cleaning up the corrosion, the only problem was replacing them with small enough substitutes. Howev­er, after all that effort, when I was sure I was home and hosed, I was shocked to find that it still wouldn’t eject. Time for thinking The moment I was dreading had arrived – I was actually going to have to get technical. I had already established that the cap­stan motor really was OK, as it worked in all functions except eject – it just wasn’t being switched on. It wasn’t easy to work out which wires were responsible for switching on the capstan motor from the servo and syscon circuits so I decided to start with the mode select switch which deter­ mines, via the loading motor, the control of all the various functions. I established that the eject and cassette-in modes occurred when the switch was in the “d” position, when the truth table gave a zero for the Data 1 and 2 buslines and a 1 for Data 0. The switch was actually built with four connectors which were, from left to right: common, Data 2, Data 0 and Data 1. As a result, I expected to see 5V on the third switch terminal (or leg) only. However, this wasn’t the case. Instead, legs 1, 2, and 4 were all high and leg 3 low – a mirror image! At first, I put this down to the switch not quite being in alignment so I checked it again – it was perfect. I then confirmed that all the other functions in the truth table were correct. I checked the DC resistance but all I could come up with was that there was something wrong with the “d” position, especially when compared with the original switch. Eventually, I came to the conclusion that the new switch was faulty and so I refitted the original while I ordered another. And after all that messing about, the original now worked per­fectly. Now I must emphasise that the two switches looked identi­cal, because the riddle was solved when I reordered a My next story is about Mr Wilson, a customer who has re­tired. About 10 years ago, he treated himself to what was close to the top of the market; a complete Sharp V1 stereo system. This consisted of a modular hifi audio unit with an unusual two-side linear tracking record turntable (yes, it had two pickup arms) and a remote control system – all heavy stuff in the late 1980s. Matching this, and connected to it, was a 63cm stereo monitor-style TV set and a hifi video recorder, the whole lot mounted in a custom-made shelving system. The thing that really dates it all now is the colour which was silver. Nowadays you can have any colour you want, as long as it is charcoal grey or black. Not long after Mr Wilson acquired the pride of his life, it was damaged by lightning. Although everything else was fixed, the VCR was deemed to be a write-off and so his insurance company gave him the go-ahead to get a new one. Naturally, he chose another Sharp, this time a VC-6F3X. Unfortunately, this model was in black and no longer matched the rest of his system but he appreciated the additional features it offered compared to the VC-5F3X that had been destroyed. Recently, he brought it in for a service as it was chewing tape and needed new belts and an idler. All this was straightfor­ward and everything was going to plan until I decided to blow out the accumulated dust with an air compressor. This required only a gentle wave of the air-gun all over to bring it back to a clean state. This done, I confidently boxed it all up and put it aside for soak testing before completing the paperwork. JUNE 1999  29 Imagine my horror when I switched it on and found that I had lost all the sound in both the play and EE modes and that the LED meter display was no longer functioning. Trying not to panic, I opened it again and checked all the plugs and sockets to see if I had accidentally pulled any out. But no, and there was absolute­ly no sound coming out, not even from the AV output or the head­phone socket. The only clue that anything at all was happening in the audio chain was that the stereo LED indicator still came on for each channel. The picture itself was great. This all indicated that the audio signal must be reaching the stereo decoder, so I decided to start investigating PWB-1, which was the top board and is easy to access. Using my amplifier probe, I was able to trace the audio signal all the way up to the Input Tuner/Line analog switch (IC6101). This device is a TC4066 which is sometimes unreliable but fortunately easy to obtain. The sound went all the way to pins 4 and 8 but no further. Similarly, sound injected into the AV input reached pins 1 and 11, so with a small flat bladed screwdriver I shorted pins 1 & 2, pins 3 & 4, pins 10 & 11 and 30  Silicon Chip pins 8 & 9 in turn but there was still no sound. I was about to replace the IC itself when I decided that it wouldn’t hurt to be a bit more technical and check a few voltages. First, I checked the switching signals on pins 5 & 6 and pins 12 & 13 with a voltmeter to find nothing there. I then checked the +12V supply (Vcc) on pin 14 but this was absent also. At last I was onto something. All I had to do now was trace this 12V rail to its source and find out why it had disap­peared. Of course, I was still expecting something like a loose plug or a switch parked in the wrong position. The 12V rail comes in on plug 1M2 which comes from BA11. As there is a large wiring harness, where was BA11 situated? Simple, look at the wiring diagram and sure enough it is shown coming from PWB-B, the audio board. But, in reality, it doesn’t. It took nearly half an hour to discover that this is an error in the schematic diagram. Instead, the 12V rail actually comes from PWB-F, which is in a completely different location underneath board PWB-1 instead of a wired audio module on top of PWB-A (the manual is not very forth­coming with infor- mation about each board’s location). Anyway, back to PWB-F. The 12V source was Q6311, which was part of a switchable regulator circuit whose source was AT17V from BD-1, which was connected to plug AS1 on main board PWB-A. Did I mention that access to this board wasn’t easy? Well, it wasn’t – I had already visited it once in the mistaken belief I was going to PWB-B and had only just put it all back when out it had to come again. The circuit for PWB-A is drawn out over two full A3 pages, so it took a little while to work out that the 17V rail comes in on AF7 from the power supply PD-1. This time I had the 17V so there was a break between the two plugs. Using a voltmeter, I found that the 17V disappeared about 25mm from AF7 and never reached AC1, AW1 and AS1. In fact, it looked as though a link was open circuit. Unfortunately, the link could not be seen from the component side as the plastic cabinet protruded over this area – not to mention the wiring harness to six plugs in the vicinity. And so I was forced to remove the main board PWB-A. This is a major undertaking involving screws, clips, wires and an awful lot of swearing. Eventually, I had the assembly and its three daughter boards and tuner out on the bench. A quick inspection of the area involving the link (357) soon cleared up the mystery. There was a spot about 25mm in diameter of severe green, black and white staining, where corrosion had taken place from an unidentified toxic liquid. After cleaning off the debris with every solvent known to man, I could see that the link had in fact disappeared completely, leaving tiny fragments in the pigtail holes to the PC board. After replacing the link and cursing some more while I got it back together again, I found (to my relief) that everything now worked properly. But how did all this happen? How did a small amount of liquid get into this location without touching anything else, especially as the lid and two other boards overhang this area. Well, I can only surmise that it dripped down the side of the plastic casing, even though there were no other marks. It guess that it could have been water from a pot plant and but why did it only decide to fail when I used the air-gun? I can only put it down to Murphy’s law and move on. The really tricky part was explaining all this to Mr Wilson. Kiwi power And now for a change, here is a contribution from a fellow serviceman – S. W. in Hamilton, New Zealand. I well remember reporting a similar catastrophe that occurred here some years ago, on the NSW South Coast . Anyway, here’s S. W.’s story. I was awoken early one morning by a loud bang. Being of the cautious nature where loud bangs are concerned, I made an attempt to determine the source. It was a wild, stormy night, so the first thing that came to mind was the power. Everything in the house was functioning OK and I checked the meter and distribution boards. Everything appeared to be in order, so I went back to bed. Later that day, I had a run of dead appliances in for re­pair. It turned out that a tree had fallen on the 11kV lines that feed our area and brought them down on the 230V lines underneath, sending 11kV through everyone’s houses and businesses. It was all very messy but I got off scot free – technician’s luck, I guess! Most of the appliances were TV sets, followed by microwave ovens, surge protection devices of the plugin variety, and stereo systems. In the majority of TV sets, the mains fuse had exploded into a molten mess and the current limiting resistor (usually 5W or 7W wirewound) in the power supply had simply gone open circuit. This is interesting, given that these components are on the other (appliance) side of the mains switch and that these sets were not turned on at the time. In every case, the high voltage had jumped the switch contacts and into the circuit. Several sets also lost chopper transistors and bridge rectifiers or sets of diodes on the input side of the power supply. Some TV sets and almost every microwave oven had varistors fitted on the mains input filter boards. These had all suffered and bits of the varistors were found scattered in all directions. One of the TV sets was a National, which was imported from overseas and had an auto-adjusting supply (110V-230V). It must have had a hernia when it saw 11kV and it took out the current limiting resistor, four diodes and a Triac. JUNE 1999  31 Serviceman’s Log – continued The surge protectors were deemed write-offs; it was cheaper to buy new ones than to repair the dead ones. The microwave ovens suffered varying degrees of damage. In addition to the faults listed above, several ovens had the primary winding on the low voltage transformer destroyed. The stereo systems had tracks blown off the PCBs and some lost varistors as well. It is interesting to see that more and more equipment is now being fitted with varistors as a form of spike suppression. The damage to equipment was fairly limited in this in­stance, due to the surge being spread over a wide area. I have seen the results of a similar situation involving just one rural road where the same thing happened and suffice it to say, there was nothing left of the gear. It had just vaporised. The real damage was caused by the meter boxes being blown off the outside walls of the houses and landing some 5-6 metres away. Inside the houses, distribution boards caught fire and set the interior alight. Red herring But back to the present and an encounter which I’ve called “The Red Herring”. Later that week, a Sanyo 34cm model C14ZA25 came in. The owner said that it had stopped working the night of the storm and he’d taken it to another serviceman to have it looked at. When he’d gone to pick it up he was told that the price t Shop soiled bu ! HALF PRICE was in the region of $120. He wasn’t prepared to pay that much and the serviceman concerned “took the parts out that he’d replaced” and gave the set back to the customer. I agreed to take the job on the theory that the removed parts would be easy to identify and it would cut down the amount of work I had to do. The following day, I opened it up and inspected the under­side of the PC board. R502, a 3.9Ω 6W resistor in the power supply, had been taken out and the solder around a blank area marked as transformer T581 had also been disturbed. But there was no actual transformer on the board. A check of the rest of the board showed that no other parts had been replaced. At that stage, I remembered the price that he’d been quoted and came to the conclusion that the transformer must have made up the bulk of the cost. I rang the local Sanyo parts supplier to check the cost of a replacement transformer, only to be told that he could find no reference to T581 in that particular set. I went back to the service manual and opened it to the inside cover which shows the basic set layout (not the circuit). And right there in the power supply section was T581. It is shown as a small step-down transformer, used to supply the low voltage parts of the circuitry when the set is in the stand-by mode. It seemed logical that it could have failed, as it would be connect­ed di- rectly across the mains input to the set. The front cover of the manual specifically says “New Zealand” in brackets under the model number so I knew I wasn’t looking at a universal manual or a copy of a manual for a different market. I was still not satisfied and called Sanyo’s head office only to be told that they, too, could find no reference to a T581. “But it’s shown in the manual”, I said. “Hmmm, so it is”, came the reply. I went back to the manual and took a look at the circuit diagram proper. And surprise, surprise – there was no sight of T581. Now I was really confused. It appeared as if it had been replaced, it was in the layout but not in the circuit diagram, and no one could reference it. I put the set to one side while I worked on other jobs and when I came back to it, decided to have another look at the PC board. On closer inspection, I soon discovered that the tracks that led from what would be the secondary side of the transformer weren’t actually connected to anything! It was definitely a furphy! I replaced the 3.9Ω resistor and the set sprang to life. In hindsight, the solder on the holes marked for T581 might have been disturbed purposely to throw the next poor bloke who looked at the set right off the trail. It certainly worked! In the end, the only part that had to be replaced was a 75 cent resistor. The customer was more than happy with the bill and I am a bit more wary of service manuals and red herrings! SC 14 Model Railway Projects THE PROJECTS: LED Flasher; Railpower Walkaround Throttle; SteamSound Simulator; Diesel Sound Generator; Fluorescent Light Simulator; IR Remote Controlled Throttle; Track Tester; Single Chip Sound Recorder; Three Simple Projects (Train Controller, Traffic Lights Simulator & Points Controller); Level Crossing Detector; Sound & Lights For Level Crossings; Diesel Sound Simulator. Our stocks of this book are now limited. All we have left are newsagents’ returns which means that they may be slightly shop-soiled or have minor cover blemishes. SPECIAL CLEARANCE PRICE: $3.95 + $3 P&P (Aust. & NZ) Order by phoning (02) 9979 5644 & quoting your credit card number; or fax the details to (02) 9979 6503; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. 32  Silicon Chip