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SERVICEMAN'S LOG The aircon that nearly made me lose my cool Like other appliances, air-conditioners won't last forever. But spending a bit more can sometimes leave you with a longer lasting and better made device. However, all good things must come to an end, as our 15 year old aircon started to take flight. I think I’ve mentioned I’m involved in a renovation project; I’ve been working on it whenever I can for the last five months so it does tend to come up in conversation. For example: Friend: “How’s the renovation project going?” Me: “$#<at>$%#!!!” Sprucing up a house from the ground up is not easy at the best of times, let alone in the middle of a harsh Christchurch winter. On the bright side, the project is excellent training for a multitude of DIY disciplines. In the two years since we moved out, the tenant had run it down – a lot. One expects natural wear and tear but dug up lawns, cutdown trees, damaged paintwork and greasy surfaces are beyond the pale. It was while I was cleaning some of their old junk from the side of the house that one of the two outside compressor units for the house’s air-conditioning system burst into life, making such a terrible squealing noise that I just about had a coronary. We’d installed these units some 14 years earlier so they’d done plenty of work, and while they were now well out of warranty (by about four years), we hadn’t had a problem with them until now. The noise this compressor unit was making now was something else though. Flashback: before the quakes When I called my acquaintance in the air-conditioning industry all those years ago for a quote, he recommended a Daikin system as they had a good reputation and an excellent (10-year) warranty. Admittedly, they were more expensive than other brands, but we’ve always gone by the philosophy that spending more at the beginning often saves money in the long run. In other words, don’t be penny wise but pound foolish! This strategy has usually paid off, well, most of the time anyway. But that’s another story! siliconchip.com.au Australia’s electronics magazine Dave Thompson* Items Covered This Month • • • • Air-conditioner repair One smoking radar Yamaha RX V450 receiver repair Car fob repair *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz When I said earlier that we had installed the air-conditioning units, it was actually our professional acquaintance that I have mentioned who did the installation. Having had a look at our place, he decided that the outside units should go at what he called the back of the house, which is actually the side, where a narrow strip of wasted land and a fence separates us from the neighbour’s property. That sounded fine to me and we signed off on the quote he sent us. However, a few weeks later, on the day of installation, I arrived home from work to discover the installers had put the compressor units literally on the back of the house, facing our grassed backyard and the patio/BBQ area. They’d made an impressive and very clean job of routing the gas and power lines through walls, over the roof and under the house to the various components, but the blasts of frigid air being chucked out over the patio meant it would be winter there all year round! I was also surprised by the sheer size of the compressor units which now took up a large portion of our patio. This simply wouldn’t do! My wife almost had a coronary when she saw them, but by that time I’d called my mate and asked him why the compressors had been placed there, thinking that perhaps the installers had hit some snags that meant they couldn’t be installed on the side of the house, where they could blow cold air onto the paling fence and drain water into the unused grass strip. September 2018  61 Do you have any good servicing stories that you would like to share in The Serviceman column? If so, why not send those stories in to us? We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. was stolen from the wreckage of a building by gang members doing demolition working, while the owner watched, kept away by police and army security who held him behind the cordons for his own safety. This POS system turned up installed in a backwater pub somewhere up north. Nobody was ever prosecuted for this blatant looting and there were many, many other instances of this happening. We’d paid a fortune to have the heat pumps installed before the quakes, so why leave them? Insurance wouldn’t cover the costs, as most insurance companies were being hammered senseless by quake claims (some obviously fraudulent), to the point some required government bailouts. Of course, aircon systems are supposed to be professionally removed, with the gas recovered properly to avoid pollution, but the fact that the gas lines had been ripped out of the compressor units and were left dangling in mid-air meant there was no gas to recover. So I had no qualms about removing everything myself. I didn’t know whether they could be used again but I wasn’t about to let someone nick them and profit from my loss. I was therefore very pleased when Clary looked at my pile of components and told me that he could reinstall them, and for a fraction of the cost of either getting new/refurbished units or the cost of hiring an aircon company to come and do it. And so it was Clary I called when I heard the noise this older unit was making. Given the current state of affairs where appliances seem to be considered “consumables”, designed for replacement rather than repair, I was fully prepared for the fact the motor might not be available. But in that case, I’d either try to replace the bearings, or ask Clary about re-purposing a different motor for this unit. Surely, given the similarity between different aircon models, it wouldn’t be too hard to locate a similar motor that would fit. While neither of these solutions would be ideal, shelling out for a second-hand compressor unit wouldn’t be much chop either, so I sent him a PXT (Multimedia Messaging Service) of the label on the side of the compressor and hoped for the best. Within a few hours, he’d called to say he could get a new motor assembly for a trifling Australia’s electronics magazine siliconchip.com.au He let out a stream of expletives (some of which I’d heard before, while others must have been aircon industry specific) and said he’d be around to check it out. Sure enough, he soon rolled up with the two navvies who actually did the job and made profuse apologies for his employees’ lack of apparent intelligence, for mistakenly putting them on the actual back of the house. I was going to point out that he had written “back of the house” on the quote but given the circumstances (and his extensive vocabulary), thought better of it. He promised to make things right and a few days later the guys were back, with a couple of others to assist and had soon relocated the compressors to their current location, with power and gas lines re-routed and any old holes nicely filled in and even painted. And there they have lived and worked happily for nearly fifteen years, until the day I was moving rubbish and the fan started up and just about caused an underwear change. Back to the present problem The noise was like a jet taking off, winding up to a very shrill level. I immediately flicked the outside isolation switch off and the fan ground its way to a stop. How the tenants had put up with this awful noise, given that one of their bedroom windows was almost directly above this thing, was astonishing. Even more concerning, how did the neighbours put up with the noise without complaint? Admittedly, there was a driveway separating the neighbour’s house from the paling fence but as the crow flies, it was only about four meters to their living room. With the air-conditioning running in our house, the noise must have been truly annoying in theirs! No prizes for all you diagnosticians correctly guessing the cause of the noise; any serviceman (or enthusiast) worth his or her salt will be shouting: fan-motor bearings! Well, that’s what I thought, so my first job was to call my new air-conditioning specialist Clary, who had installed heat pumps in our new place. My knowledgeable assistant I’d met Clary through a builder friend and when I discovered that he could install heat pumps for us at our new home, I was sold. We already had the heat pumps as we’d stripped them from our quake-damaged workshop rather than leave them for the vultures that were picking over the broken bones of Christchurch businesses at the time and selling their swag in pub car-parks around the country. As an example, a multi-thousand dollar customised café POS system Servicing Stories Wanted 62 Silicon Chip $120 plus tax and shipping, which sounded like a pretty good deal. In the meantime, even though it was below zero most mornings I went to work on the house, I avoided using the heat pump, not because it might get damaged further but because I was embarrassed about the noise, and I didn’t really want any trouble with the neighbours. It took a few weeks for the motor to arrive and Clary messaged me when it did, asking if I wanted him to install it, or do it myself. I asked him the likely cost of him doing it and he reminded me that I’d looked at a circuit board for him about a year previously, and because I hadn’t charged him for repairing it, he would change the motor over for me for nothing. What a surprise, as I’d forgotten about doing that little job for him, and just goes to show what a little karmic investment can reap. I pledged to help him though, partly out of a sense of duty and partly out of professional interest, because I’d never seen the internal workings of one of these units before. Getting to the motor He arrived early one clear-but-bitterly-cold morning and we set about swapping out the motor. He first fired the thing up and we chatted as we waited for the compressor to kick in and the fan to start. When it did, we weren’t disappointed and Clary immediately agreed with my diagnosis that the fan motor bearings were almost certainly the cause of the noise. Getting things apart on the compressor unit looked quite straightforward, with just a few sheet-metal screws holding the exterior panels on. I thought this job would be a cinch; talk about your famous last words! Clary started on one screw with a large Phillips head screwdriver and immediately it became clear that the screws were a little tight. I grabbed another, smaller screwdriver and started with other screws, while he braced himself and cranked harder on his stubborn fastener. You can imagine the grunting and swearing, and Clary was the same, especially when his screw head sheared off, leaving the screw’s threads fused to both the panels and the rivnut-type threaded insert. While most of the screws had combined Phillips/7mm hexagonal heads, suitable for a socket or crescent wrench siliconchip.com.au (shifter for you Australians), as the screw had failed using just a screwdriver, I expected it would shear even more easily using a socket wrench. I had no luck at with any of the other screws with my smaller driver either, so we resorted to a liberal application of penetrating oil spray on all visible, to-be-removed screws. While the oil did its work, we did manage to remove the plastic front shroud, which used beefier, coarser-threaded screws. After the four shroud screws are removed, the panel slides upwards and this releases several plastic clips holding it to the front of the compressor unit. Without knowing this trick, I would likely have resorted to levers and prying to release it, so almost straight away Clary’s knowledge and experience made things easier. Removal of the shroud cover exposed the fan, a large-diameter, threebladed plastic unit. I was surprised at how small the now-visible motor was, given the size of the blades. Once again, Clary’s experience showed as he mentioned that the fan nut, a nylock-type, might use a lefthand thread. As it happened, it didn’t, and we discovered that because the nut was quite loose. Clary had a socket for this task, assuming it would also be tight, but he found when he applied the socket that he could actually spin the nut off by hand. He’d mentioned that sometimes the fans can be a real pain to remove from the motor shaft, but in this case, the nut spun off the usual way and the fan came off just as easily, revealing the motor and mounts behind. By this time, we hoped the penetrating oil had done its job, as it was obvious we’d have to remove the top, front and one side panel in order to unplug the old motor’s lead from the controller board. This sat inverted near the top of the case in a water-tight plastic box. Having removed that, we would need to route the new motor’s cable and plug it back in. They certainly could have designed this a bit better, given that the cable on the motor needed to be about one metre long in order to snake around the plastic PCB case to reach the buried socket on the opposite side! The next screw we tried to remove also failed but this time it took the threaded parts with it, leaving a larger hole than before. On viewing it, I Australia’s electronics magazine September 2018  63 theorised that dissimilar metal corrosion had, over time, welded the screw, panel and insert together; whatever the actual cause, it was certainly stuck fast. We got half the case screws out without damage but the motor screws, which are a smooth-shafted bolt with a small threaded piece on one end, all sheared off in the pressed, sheetmetal mount. What fun this job was becoming! In the end, we just went for it and whatever screws we had to drill or wind out with pliers we coped with. Fortunately, none of the fasteners were critical, except perhaps the motor mounting bolts which pass through and tighten onto rubber mounts to keep vibrations to a minimum. For those, we just drilled out the jiggered holes and re-threaded them for the slightly larger threads of some new bolts that Clary had in his bits boxes. It helps to have good tools Whilst helping him to find new screws, I couldn’t help but admire the contents of his work van. Talk about tool porn! He had tools and gas-fitting stuff I never knew existed and his van had just about any tool or device you’d need for installing heat pumps. While it can be difficult to justify the outlay for some of these tools, given you might only use them once in a blue moon, it’s a fact that when you need a specific tool for a specific job, and nothing else will do, then you’d be glad you bought it. Well, that’s my theory anyway, and is what I usually try to tell the wife when I want to buy some new widget or tool for my workshop! That said, it does get to a point where even a workshop isn’t big 64 Silicon Chip enough, so there must be a line there somewhere, I just haven’t found it yet. The job changing the fan motor was not overly difficult but it wasn’t simple either. The old motor growled when the shaft was manually turned and the new fan was almost completely silent when we fired it up, so that was definitely the problem. Hopefully, the neighbours appreciate their newfound peace and quiet. I doubt they realise how much work went into achieving it! A smoking radar transformer R. E., was responsible for repairing large radar systems – not a job for the faint-hearted! Some years ago, he found an unexpected fault while performing the first six-month service on a newly installed radar. Here's his story... This new radar system had replaced an older unit that had been in service for many years. It was a 250kW unit, one of many similar radars operated by this particular government department. It comprised a transmitter/receiver unit and associated scanner control gear, all located in an equipment room on the ground floor of the building, except for the scanner itself which was mounted on the secondstorey roof. The scanner was connected to the equipment room via a rather long and convoluted waveguide, with bundles of cabling carrying power and control data, both of which I had helped to install. By this stage, I had the service on this type of radar down to a fine art, which included greasing of the mechanical gear trains in the elevation and azimuth system, removal of the Australia’s electronics magazine slip ring brushes and cleaning of the slip rings that carry the power to, and data from, the elevation part of the radar scanner. I also checked all power supply voltages and ran checks on and tuned up the radar transmitter and receiver. This ensured that the transmitter was both on frequency and putting out the correct power and that the receiver was tuned correctly and had the specified sensitivity. The mechanical service, while messy, was simpler on this radar than on the older unit that it replaced, as the previous radar had two large oilfilled gearboxes for the azimuth drives (one high speed and one low speed) plus an elevation gearbox, all of which had to be drained and refilled every six months. There were various points where I had to inject fresh grease, too. The service on this new radar initially went well, as you would hope and expect with a new radar. The entire process took two days, with breaks for operational requirements, as at times it had to actually be used for the purpose for which it was installed, during which I busied myself with work on other equipment at the station. I was finished with the radar itself around lunchtime on Friday, which was good since I had a 400km return trip to get home for the weekend. Just one check remained – I had to test the station's backup generator, which had only been installed just prior to my visit. It had been tested off-load by the contractors who had installed it but they had left by the time I was ready to load test it. So, having warned the station staff, I went out to the station meter box and switched off the three-phase supply to the site. After a short delay, the generator started and I checked that the oil pressure and other readings were OK, then wandered back into the office to make sure all the equipment was still working properly. When I stepped back in, the first thing I noticed was a burning smell, which did not initially alarm me as the station staff often produced odd smells when they were cooking. But as I walked into the radar equipment room, I was horrified to see smoke pouring out of the radar control rack and hurriedly switched off all power to the radar. I could hear a crackling sound coming from the back of the radar interface siliconchip.com.au and as the smoke slowly cleared, I saw a toroidal transformer that had clearly cooked up. This was odd as it surely couldn't be a coincidence that this happened right when the generator fired up, but the only thing that had changed was the power source. A quick check showed that every other piece of equipment that was in the office, and on-site, was operating perfectly well. I checked the power coming from the generator but each phase was close to 240V, as expected, and I couldn't find any other issues using the equipment I had on hand. Anyway, clearly, I would have to replace the transformer which was now the extra-crispy type. To start with, I would have to remove the radar interface, which connected the control computer to the rest of the radar, to get a closer look at the burnt transformer. I was relieved to find that we had a spare transformer available so I at least had a chance of fixing the radar that afternoon. I started by drawing a diagram showing which connectors went where at the rear of the interface. I had learnt the hard way not to rely on my memory of what goes where, as many of the cables were not labelled. Since it was a new design and only recently put into operation, I knew nothing at all about this system and was more than a little hesitant about working on it. But I really didn't have a choice at this stage. Access to the components was by undoing numerous screws on the top panel and flipping the large lid over to reveal the components all mounted underneath that top panel on solder tag strips, none of which were labelled, and all connected via hook up wire, most of which was the one colour – pink. AZ synchro 18TRX6 Radar scanner synchros 18TRX6 EL synchro After refitting the upper board, remounting the interface in the rack, and then reconnecting the myriad of cables to the rear of the unit, I was ready to power it up. At this stage, the generator was still providing the mains power. I decided to risk powering the radar back up while still on generator power since it was the only way that I could think of to prove whether the generator was the root of the problem. I crossed my fingers and flicked the breakers. The radar initially seemed fine but after about 30 seconds, I could once again hear the crackling sound of overheating insulation and a quick glance at the interface showed that the replacement transformer was starting to cook. And the fuse had not blown. This was not totally unexpected and suggested that the fault was not in the radar itself, but something to do with the generator. I had no option but to once again power down the radar and ponder what to do. Clearly, the radar could not be operated like this. Even if I had a second spare transformer, I could hardly fit it and leave since if the mains dropped out and the generator came on, that would be the end of the radar again and could possibly result in a fire. In fact, it was lucky that this was the first time the generator had been used. Well, if these toroidal transformers would not work on the generator power, perhaps a different type would. Certainly, the rest of the transformers in the radar, and other equipment on site, was handling it without a problem. I realised that the 95VAC required for the synchros was similar to the 110VAC used for American mains. There was a very good chance that the local Dick Smith (remember them?) might have a step-down transformer meant for powering American equipToroidal 240V from transformer ment in Australia and that could be mains or generator 95V suitable for this job. 50 cycles By this stage, it was getting close REF to 4.30pm, so I jumped in the car and S1 S2 S3 tore down to the store before they AZ synchro closed and was rewarded with a small step-down transformer complete with to digital converter mains lead and plug. Its 100V output was not exactly as specified but I figured the worst that could happen EL synchro was that the synchros might run a little warmer. to digital converter I wired this in place of the toroidal transformer. The result was not pretty A diagram showing how the toroidal S1 S2 S3 but I was pleased to see that turning transformer drove the "synchros" in the radar. siliconchip.com.au All I could do was use my multimeter to figure out which connection went where. Then when I was finished, I would need put it all back together, laboriously re-connecting all the plugs, wait for the radar's five-minute warm up-timer to finish, then apply high voltage and see if it was working. If not, I would have to start the whole tedious process again. At least the interface on this new radar was less complicated and easier to access than the old one. So, I dug into it, removing all connectors, undoing the interface rack mounting screws and dragging it out on top of a trolley, where I could work on it. During this process, I labelled the connectors and sockets so I would have a reasonable chance of putting it back together properly. I could now see the damaged transformer and the fact that it had gotten quite hot was obvious, with melted plastic insulation and other signs of heat stress. My circuit diagram showed that the purpose of this transformer was to supply 95VAC to the radar synchro receivers. These are small devices somewhat like motors except that they are used to determine the rotational position of the radar. I checked the resistance across the transformer load and got a reading about half that which I measured from a spare synchro; I had expected this as the transformer drove two synchros. This suggested that it was not a short circuit at the output which had caused the transformer to burn out. I swapped in the spare transformer and added a temporary unofficial modification: an inline fuse holder and fuse in the secondary of the transformer, on the cable powering the synchros, just in case I was wrong about the transformer load being the problem. Australia’s electronics magazine September 2018  65 66 Silicon Chip Mentioning this problem to the main workshop further south seemed to provoke some disbelief until later the following year they encountered the same problem at an identical new radar installation, whereupon they contacted me to let me know that the same thing had happened to them! is used to switch power to the main transformer. The circuit operation was difficult to understand at first. Current from the mains Active flows through a 22nF capacitor and 2.2kW resistor to a 10V zener diode and this arrangement then feeds a 9.3V rail via diode D4 to power a 4013B flip-flop which drives the gate of Mosfet Q1. Q1 switches current through a small transformer, T1, via bridge rectifier D1 and this transformer provides a 12V standby rail for the main PCB. I hooked up the sub power PCB to the mains via an isolation transformer. The voltage across Z1 was only 6.4V, not 10V as I expected. The circuit seemed to work to some degree as there was 8V across C2. I decided to remove C1 and measure its value as the coupling capacitor in this type of circuit has proven to be a problem before. C1 measured only 10nF, not 22nF as it should be. I replaced it with a mains-rated (X2 class) 22nF capacitor and powered up the board again. I then observed 10V across Z1 and 12V across C2. The voltage across C2 slowly dropped under load until it fell low enough to make the optoisolator Q2 turn off. This allowed Q1 to turn on for a short time to top up C2. So the circuit was designed to save power by only running transformer T1 when it A N was required. Yamaha RX V450 5.1ch receiver repair J. W., of Hillarys, WA, decided to help a friend out by repairing a cherished Yamaha surround sound receiver. He was rewarded for his generosity in liquid form... A friend asked me to look at his Yamaha RX V450 5.1-channel receiver. It was quite a few years old and had recently become difficult to switch on. Sometimes it would power up but other times would take a number of presses of the power button. Now it would not power on at all. I removed the cover and found that the incoming mains supply went to a small PCB. This seemed like a good place to start. I removed the PCB and examined it through my magnifying lamp but couldn't see anything unusual. At this point I decided to try to find a circuit diagram on the net, I located the one shown here. The small PCB was called the sub power board and was responsible for providing power to the main PCB to run the infrared receiver and the coil of a relay which R1 2k2 Yamaha PSV sub-board circuit C1 0.022 D1 Q1 U1A 4013B 3 6 4 D CLK SET RST VDD 14 R4 1M0 5 VSS R3 220k Q Q 1 T1 R2 220k 2 7 D2 9.3 V Z2 U2 R5 2k4 D4 C2 50uF 9.1 V RELAY Z1 10 V R6 C3 50uF 2k2 Q2 TO MAIN POWER TRANSFORMER 6 5 4 3 2 1 the radar on again resulted in full operation and no burning smell. I hung around for an hour or so monitoring the operation to ensure that nothing untoward happened with this new transformer in circuit, then took off for the day. Of course, this was not a permanent solution, but it did get the gear back on the air, which was most important, and would allow me to return home the following day, once I had checked the operation again in the morning to confirm that all was still going well. Back in the workshop the following Monday, I ordered both a replacement toroidal transformer for the unit and a spare for the spares cupboard. I then contacted the contractor responsible for the supply of the generator to let them know that something was amiss and that the generator installation was not acceptable. I also contacted a transformer manufacturer to chat with them and they told me that a “shorted turn” that can occur with toroidal transformers, depending on how they are mounted. This sounded very much like the problem that I had seen, though how it occurred was something of a mystery to me. I should mention that toroidal transformers were pretty new technology back then and I didn't yet understand them all that well. Almost all the previous equipment that I had worked on used the older-style E-I core transformers. The contractor replied sometime later that week that they had found that the office earthing had not been done correctly at the generator but that it had now been rectified. My theory is that the Neutral from the station was tied directly to the Earth at the generator, which somehow caused a shorted turn effect via the metal mounting bolt and plate that was holding the transformer to the earthed metal base plate. But truth be told, I really do not know for sure and now that the radar was completely operational again, I had other things to think about. Once the replacement toroidal transformers turned up, at the next possible opportunity I returned to the station and fitted the specified transformer and a test run with the generator showed that the radar would now run off the generator with no problem, which was a significant relief to me. P1 TO MAIN PCB Australia’s electronics magazine siliconchip.com.au I reassembled the receiver and ran it for a few days. The difficulty switching on had disappeared so I gave it back to my friend, who now has his surround sound system working again. He generously came around with a bottle of scotch for my efforts. Editor's note: failed X2-class capacitors have become a theme in our Serviceman contributions. We think it must be due to their "self-healing" properties, where damaged sections of the metal plating will burn away so that the capacitor does not short the mains. But this results in their value dropping and eventually, it will drop far enough to cause the device to malfunction. What causes the damage in the first place? It may be that the capacitors are poorly manufactured and simply degrade over time but it seems more likely that it's due to voltage spikes in the mains, from thunderstorms and such. This type of circuit for reducing the receiver's standby power was used for many years in Yamaha products. They were one of the earliest manufacturers to reduce standby power of their appliances. The resulting standby power figures are impressive, at around 100mW. This is made possible by switching mains across the transformer periodically, minimising the average magnetising current. Car remote repair R. W., of Lakes Entrance, Vic, found that even a simple repair job can be satisfying and can save quite a bit of money too – especially when the item that's being repaired is in the automotive realm. Replacement electronic parts for cars can be surprisingly expensive so fixing them is often worthwhile... Cars and oil are usually a good combination but this time, it lead to an unusual service challenge. My daughter now owns my father's old Nissan Pulsar and it was one of the early models that adopted remote locking, boot release and a panic button (which sets off the alarm). It has been a very reliable runabout. But after spending a week or two in Melbourne and borrowing the car on numerous occasions, I became aware the remote locking fob was not reliable and while the lock button would always work, unlock often did not. siliconchip.com.au These things are notoriously expensive to replace so a repair was definitely worth a try. Using a coin, I cracked the fob open and found a large button cell in good condition. I bought a new cell and replaced it but no luck; it made no improvement. Having to think a bit harder, I inspected the fob and prised the PCB out of silicone insert which held it in place and also formed the rubbery buttons that poked out the other side. To my surprise, the whole thing was covered with a greenish goo. At first it looked like corrosion, but the the silicone cup was actually full of oil. It looked like clean engine oil and it was everywhere. My daughter assured me she knew nothing about it so I am guessing the key fob's oil soaking had happened before she started driving the car. While there was no evidence of corrosion affecting the operation of the remote, the oil had been there long enough to stiffen and gum up the switches. Strangely, there was no oil at all on the battery side of the fob. Perhaps the silicone part had formed a gasket, stopping it from getting into the back of the remote. I washed the oil off the PCB and silicone by applying turpentine and Australia’s electronics magazine scrubbing it with an old toothbrush. The brushing must have been overly vigorous though, as one of the metalbodied SMD tactile switches was left with only one leg out of four still attached. Using my finest soldering tip, I re-soldered the three detached pins on one switch and refreshed the solder on all the other switches. Then, using a fine hair brush, I dabbed fresh turpentine on each switch in turn and using a metal probe, quickly pressed the switches off and on many times. This action released goo from inside the switches that I then wiped away. Cycling around the switches in turn, washing and clicking gradually flushed all the goo out, giving a satisfying click when each was pressed. I repeated this over and over until I was happy the turpentine was clear. I then used methylated spirits to give the PCB a final clean, to remove any turpentine residue. My daughter and I were both pleased to find the clean new fob worked properly again. While literally a small job, it was a most satisfying challenge and my father would have surely been pleased too. He was of the conviction that nothing could be thrown out unless it had been repaired at least two times already! SC September 2018  67