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SERVICEMAN'S LOG Some jobs are much harder than they should be Dave Thompson It is often the way of the serviceman that some of the small jobs turn out to be the most testing. My progressing age doesn’t help, but nor do modern manufacturing techniques which cram so many tiny components into a tight space. One reason for my increasing difficulty effecting these repairs could be that I’m getting on a bit now, and my once-dexterous hands don’t feel quite as capable as they once did. Nor do my eyes seem as sharp as when I was 20 years old. A good magnifier with a bright light (or better still, a high-resolution USB microscope with a decent-sized screen) will help with the fading eyesight. But there isn’t a lot I can do to keep my motor skills young. It isn’t as if I can’t pick up a cup or walk up the stairs without my bones creaking and groaning, like many of my martial-artist friends who practised the striking arts. They spent their careers punching and kicking each other and breaking bits of wood and bricks, and many are now feeling the effects of doing such a sport. I spent 25 years practising Aikido; one of the skills involved is learning to fall over without getting hurt, so that’ll 96 Silicon Chip set me in good stead for the future! But I am noticing a slow but inevitable decline. It’s the same when people suddenly find they can no longer run 100 meters without a rest break, or throw or kick a ball nearly as far as they used to. Obviously, this is all part of getting older, but it still affects what we servicemen do. I’ve been lucky enough to have steady hands and good tools to help with some of the trickier jobs I’ve done over the years. While good tools help, it’s the skill behind them that makes all the difference. Dad taught me to solder about the time I started talking, and I gained further valuable skills in this area working at the airline. However, much of this knowledge is deprecated now, given the massive increase in the usage of SMDs over through-hole components. Many of those SMDs are almost invisible to my old eyes. As a result, some projects and device repairs are beyond the scope of even skilled servicemen, and repairs increasingly require specialist (read: expensive) kit that many of us don’t see the value in acquiring. I recently had a quite challenging small-form job through the workshop: a Logitech mouse. Before you all jump up and down and query the wisdom of repairing something like this, it isn’t one of those 10-dollar corded jobs you buy at the checkouts at a supermarket. This 7-button wireless mouse was quite costly, and the owner thought it prudent to try to have it repaired before shelling out for a new one. The problem was the left click button; for some reason, it started douAustralia’s electronics magazine Items Covered This Month • Of mice and men • Volume control issues with an • • electric guitar kit The lab and the variac Clenergy SPH15 1.5kW solar inverter repair *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz ble-clicking, no matter how gently or firmly one manipulated the flexible plastic actuator. Thinking it could be a software problem, even though the owner had tested an old mouse and found it free of this defect, I plugged it into my machine. Sure enough, a single click of the left button resulted in a double-click action. The right button was fine, a­nd if you listened and felt the tactile difference between the two button clicks, you could sense something was up with the left one. It felt and sounded worn out. This mouse hadn’t been used all that much, so it was unusual that the button had ‘worn out’ in such a short time. Micro-switches typically have a stipulated lifetime, measured in actuations, but I have mice that are decades old and have literally travelled many hundreds of kilometres with millions of clicks. I know this because, for many years, I had a piece of software installed that enhanced my mouse’s capabilities, which also measured how far my mouse had travelled and how many of the various button clicks I’d performed. It is astonishing how quickly siliconchip.com.au the kilometres and clicks add up! Sadly, this software won’t run on Windows 10 and is now abandon-ware. Returning to the mouse in question My semi-educated guess is that the switch was just one of the small percentage of the many millions mass-produced every year that fail early. This so-called acceptable failure rate happens with everything from ovens to soldering irons and cars to hard disks; it is just part of modern manufacturing. A famous case (to computer nerds at least) is a hard drive that came out in the 90s called the Quantum Bigfoot (https://w.wiki/3AmL). For about a year, most PCs purchased came with one of these drives. My first PC had a 2.1GB Bigfoot; a massive amount of disk space at the time. The Bigfoot got its name from the large form factor it had compared to other hard drives, which were physically smaller, known as 3.5-inch drives (referring to the diameter of the platters inside). The Bigfoot was much larger, being the same width and taking up the same bay space as one of those ancient 5.25-inch floppy drives, or a slightly more modern CD-ROM drive. It had one flaw, though: it was rubbish! Most hard disk manufacturers have an acceptable failure rate for their products in the region of 2.5% or so, meaning that out of every 40 manufactured, one will fail within the first 12 months of use. That sounds pretty good, unless you are one of those who experience that failure and the data loss that ensues. The Bigfoot had a failure rate of close to 50%, which was previously unheard of. I found out about it because the Bigfoot in my desktop PC failed within a couple of months, taking all my data with it. I replaced it with another make siliconchip.com.au and model of drive, at my expense, because the company I’d bought it from had gone under. That was a common occurrence in the early days of pop-up stores selling computers in the mid-90s boom. This did teach me some very valuable lessons, though. The first: always assume a computer will fail. It is almost inevitable. If you haven’t backed up your data, how much trouble would you be in if it went ‘bang’ when you next fire it up and you lost everything? The second: computer repair guys back then were often sharks and rip-off merchants, playing on the ignorance of the average owner. Being a beginner at the time, I got burned. A little later, when I unexpectedly lost a gig working at a local TV studio, I looked into fixing computers for a living and realised that it was something I could probably do. I understood the basic principles and systems well enough, and with the arrogance of youth, I figured that I could do it. That was 27 years ago, and for the record, I probably wouldn’t have the nous to make that same decision today. But I’m glad that I did at the time. Back to the mouse again If you’ve ever had the pleasure of opening one up to see what’s inside, you were probably surprised at how little lives inside them. The bulk of your basic twoor three-button corded mouse is likely taken up with the laser Australia’s electronics magazine and (optional) scroll-wheel assembly, with their associated switches mounted to a small PCB on the bottom of the chassis, which also has the USB or PS/2 interface circuitry. It’s pretty simple stuff, and certainly not worth fixing given the ultra-low cost of them these days. That’s not to say I haven’t re-terminated cables or cleaned balls and optical wheel sensors out in my time; I have, many times. But these days, unless someone really loves their mouse and is prepared to pay to have it fixed, it will end up in the bin. This particular customer likes his mouse a lot, and since this type costs a lot more than your garden variety mouse, he was keen to have the errant microswitch swapped out. He’d had a look inside and baulked at the many PCBs stuffed with SMDs and the complex internal construction, concluding that the fitting of a new switch was beyond his pay grade. And so he brought it all to me. It turned out that I have an identical mouse stored away in my, erm, mouse storage place. This could be a stroke of luck, as it is always nice to have an identical model to refer back to, especially if the breadcrumbs I leave or photos I take along the way don’t lead me back to an easy reassembly! To be honest, I felt pretty much the same way as my client when I took the case off. It looked like a Mars Rover without the wheels, stacked with electronics on layered PCBs. Fortunately, the customer had already opened up the case; he’d done the hard work of finding the four hidden screws and plastic clips that were holding it all together. This is a classic case of manufacturers making things difficult to repair. I guess it could be worse; they could have used deeply-buried anti-tamper fasteners. Despite that, the unwary or inexperienced might just conclude that because there aren’t any visible screws holding it together, there mustn’t be any, and begin by trying to pry the case apart. Of course, this will end in tears (or at the very least, a mouse with a mangled case that won’t come apart). The two front screws are hidden behind a couple of those stuck-on Teflon bumpers many computer mice have these days. These are to help it slide more smoothly over a desktop or mouse pad. May 2021  97 You might assume the two rear screws were hidden under the back bumper, but no. Those back screws were cunningly hidden inside the battery compartment, underneath the stickers that denote battery type and polarity. The ends of the stickers had to be carefully peeled back to find and access the screw holes. The cowboy in me might have been tempted to just punch straight through the stickers with my screwdriver if this was my own mouse, but for a client, one has to maintain certain standards and decorum. So it was fortunate that he’d already done the hard work, peeling back those stickers and removing the screws. I could see the offending microswitch as plain as day at the bottom of the heap, but getting to it was going to involve removing a lot of tiny screws, most of which were different sizes and threads. The photos I took periodically during disassembly would definitely help with putting it all back together. My memory of what part went where would also be a valuable tool; thank goodness that hasn’t gone south on me yet... A challenging repair job The various boards inside the mouse were connected with a mix of those really stiff, hard-soldered flying leads and thin, flexible ribbon cables terminating into ‘backflip’ edge connectors. These connectors are very similar to what I find in laptops, phones and tablets to connect PCBs together. One problem I’ve found with this type of connector is that they are often limited-use items. If I toggle them open and closed too many times, many break, give out or won’t 98 Silicon Chip connect properly anymore. Replacing them is also very difficult for mere mortals like me. Long story short, I had to disassemble the whole mouse just to gain access to the switch in question. Replacement switches are available all over the usual auction sites online, but as I had a good collection of NOS (new old stock) microswitches, I was sure one of them would be fit-for-purpose. The bigger problem for me was removing the old one, given the small form-factor and tight spaces. Sometimes it is easier to cut the component off with the likes of a Dremel/rotary tool with a cut-off disc attachment, but there was no room for that rather ham-fisted approach here. I could just get my soldering iron’s finest tip to the contacts, but even though I could melt the solder, removing the switch was not easy. It appeared to be stuck down, likely to ensure it stayed in place for the reflow soldering process. While I had the legs unsoldered and clear of the board, the switch would just not let go. I tried soaking it with isopropyl alcohol and various contact cleaners in the hope it would loosen up; it didn’t. I had to resort to using my dental picks to try to break the bond, being very careful not to damage anything on the PCB underneath, all to no avail. It was stuck fast. I ended up breaking the switch off the board as gently as I could, but was horrified to see several of the tiny copper tracks coming with it. That pretty much ended the repair job right there. While I could see where the three tracks had been torn from, re-joining them, especially on a double-sided PCB, was not going to be feasible. While I might have been able to do it, the time involved would push the repair into loss-making territory for me. Fortunately, I had that identical mouse. After installing batteries and using the Unifying software to associate my mouse with the customer’s dongle, I figured it would be much easier to just sell him this one as a second-hand device rather than persevere with the now-damaged one. He was grateful for this option, so we all went home happy. This was one of those jobs that, if it went well, it was worthwhile doing, but as soon as something went awry, it became a non-feasible repair. As a serviceman, I have to try the former option, but I also need to know when to pull the pin on a dead-end job. Having a suitable replacement mouse in this case was just good luck. If I didn’t have one, the client would likely have had to shell out for a new one. Such is life. And I have to say that gluing components to the board might be convenient for manufacturers, but it certainly makes those parts hard to replace if they fail! Ideally they should use a type of glue that loses its strength over time or with heat, or that is just tacky enough to hold the components down for soldering but still allows the possibility of pulling it off later, should it need to be replaced. That might even help the manufacturers if they have to ‘rework’ any of their products before sending them out to be sold. An electric guitar kit with volume control issues J. N. of Mt Maunganui in New Zealand recently built an electric guitar from a kit. He had a bit of a problem with some of the electronics, and the solution was a bit unusual… Australia’s electronics magazine siliconchip.com.au All went well with my guitar build until I began playing the guitar via an amplifier. I started having intermittent faults with the volume control to one of the two Humbucker single-coil pickups. Naturally, I re-checked all my wiring to find nothing amiss. Then the volume control started working again, but not for long! So the problem must either be in the pickup or its associated volume control. However, both checked out fine. The pot measured 500kW and a normal 10kW+ for the pickup. But as soon as I reinstalled everything, it happened again. This repeated several times, with me checking and re-checking until the penny dropped. The volume control worked when removed, but as soon as I remounted it, it would not function. So it had to be an installation problem. Sure enough, on very close inspection, I noticed that this particular pot (unlike the other three), was mounted on a slightly curved part of the guitar soundboard. Consequently, when the fixing nut and washer were tightened, the pot became warped and would not function. I replaced the steel washers with rubber washers and had no more problems after that. The lab, the questionable students and the variacs D. D. of Coogee, NSW, wrote in to say that he loved the story about the Old TV Repair in Serviceman’s Log, April 2020. It reminded him of when he was a young serviceman in the 1960s, which prompted him to write the following story... Back in the 60s, I worked in the chemistry department of a university in the UK, where I was in charge of the electronics workshop. One winter morning, soon after I arrived for work, I had a call from the glassblower. He was a lovely chap and a real glass craftsman but had no real understanding of “electrics”, and I realised he was a bit scared of it. I grabbed my trusty Avometer and set off for his workshop. When I arrived, he showed me a machine and said: “the green light is on, but I haven’t turned the power on yet, what do you think could be going on?” The machine was an induction heater in a large metal case mounted on the wall, about 60cm above the bench, so he could feed glass tubes into the induction coil to heat them up. It had various controls and an on/off switch on the front panel as well as a large green indicator light. This was glowing brightly and was freaking him out. He was very worried about this and asked if I thought we should call the university electrician in case some weird power fault had occurred. I was initially puzzled because I didn’t think it was likely that the machine could be on without being switched on. I pointed out that the switch was still in the off position, but he was not convinced. I then said, “Well, I can’t see the light glowing from here.” He pulled me back over to the door and said: “look, you can see it from here.” It was only then I realised that where the machine was mounted on the wall, the sunlight from a window behind it could enter through the perforated metal back of the cabinet and make the light appear to be on! Needless to say, he was a bit embarrassed, but we had a good laugh about it and became firm friends afterwards. In fact, he became a bit of a mentor to me and helped me in lots of ways. siliconchip.com.au Australia’s electronics magazine May 2021  99 Another problem I had to solve concerned variacs. They were used in constant-temperature water baths in the teaching and research laboratories. These were magnificent brass tanks about 1m square and 0.5m deep. They had a pyrotenax heating element in the bottom, a slowly-rotating paddle wheel to circulate the water and a mercury-in-glass thermostat. They were made in-house; Ron, in the main workshop, made the tank and the paddle wheel. “Big wheels turning slow, mate” he said to me one day with a knowing tap of his nose. (I had no idea what he meant but pretended I did!) My mate the glassblower made the thermostat, which was basically a mercury thermometer with one fixed platinum wire contact and another mounted on an adjustment screw to allow the temperature to be set to the desired level. Ron wired these contacts through a relay to switch power on and off to the heater. The variac was needed because the heater had a resistance of about 10W and needed about 4A to heat the water to the required temperature. The system worked really well and could control the water temperature to a small fraction of a degree at a much lower cost than commercially-available units. The problem, however, was the users; mainly research students, who while they were very good at chemistry, could not do a simple Ohm’s Law calculation and so tended to overload the variacs. When they put a flask of chemicals into a water bath, it took a long time to warm up the contents before they could start their experiments. With the Professor breathing down their necks for results, and the fact that they often had late starts due to too much social life, there was a great temptation to wind the variac up a bit to speed up the heating process. They had a current rating of 4A, and despite being warned not to exceed 40V, the users did not seem to realise that exceeding this could cause a problem. Of course, the carbon brushes overheated and eventually failed. Each time a brush failed, damage was caused to the copper winding of the variac, and before long, the inevitable happened – a winding burned out. This proved to be the case one day when I was called to “Derek’s” lab. He had been copping a bit of flak lately from his Professor about various blunders and delays, so he was in a right panic when I told him his variac was “cactus”. To try to help him out, I offered to go to the main store and get a new one for him. I didn’t stock variacs; they were far too expensive, but there were a couple in the storeroom. It didn’t occur to me that maybe I shouldn’t just walk in; after all, I was a staff member, not a student; so in I went. I was chatting to the stores girls whose main occupation seemed to be filling beautiful old glass-topped reagent bottles engraved with the Latin names of chemicals. They were filling them from large tubs of chemicals and putting them on the shelves to be issued later (a cost-cutting measure). The manager strode up to me and drew himself to his full height. “Can I help you?” he asked. He was what I suppose you would call a dapper little man, impeccably dressed (unlike the rest of us) in a striped white shirt, tie, neatly ironed trousers and his white lab coat starched to within an inch of its life. He carried a plastic wallet in his breast pocket with black, blue and red biros and a propelling pencil. “Yes, please” I said, “I’d like a variac; I see you’ve got two left.” The girls later told me they could see the steam coming out of his ears! When he had finally regained his composure, he rushed me into his office and shut the door. “Dave I know you’re new and that, but that’s not how things are done Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column in SILICON CHIP? If so, why not send those stories in to us? It doesn’t matter what the story is about as long as it’s in some way related to the electronics or electrical industries, to computers or even to cars and similar. 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. 100 Silicon Chip Australia’s electronics magazine you know!” He proceeded to explain his “stores system” to me. He gave me a stores requisition book and a stock list and explained that four carbon copies were needed. “You fill it in, with your name, department, extension number and the details of what you want, referenced from my stock list. Then you sign it, hand it in at the stable door and we will bring your items out to you. Don’t forget to put the carbon paper in; the white copy is for my records, red for the office to charge to your account, yellow goes into storage, and you keep the green copy in your book. Understand?” Feeling somewhat chastised by all this, and as it was nearly hometime, I withdrew back to my workshop and went home, forgetting all about poor Derek waiting upstairs! The next day I returned to the stores with a neatly filled out requisition and rang the bell at the half-stable door. One of the girls came up, and I handed her the requisition. She went off with it, and after a little while, the manager came over to the door. “Sorry Dave, I can’t let you have one” he said, much to my surprise. “Why not?” I asked, “Have I filled out the requisition wrong somehow?” “Oh no, that’s OK” he said, “It’s just that I haven’t got enough stock.” This was a bit puzzling because I knew he had two yesterday and didn’t think he could have issued both of them already. Eventually, I blurted out, “But you had two yesterday.” “Yes,” he replied in an irritated tone. “So why can’t I have one?” I said. Imagine my amazement when he explained that one was needed in case “someone” wants one and the other was a pattern for re-ordering! “But I’m someone” I tried. He wouldn’t budge, however, and I felt like I had been sent off or sin-binned! Later, I found out that the only way I could get one was to get Derek’s Professor to ring down for one. Jim explained the Professor was the “someone” – his secretary would fill out the requisition, which would be sent to the stores in the internal mail and a girl would deliver the item to Derek’s lab. This was duly done, and I installed the new variac, telling Derek to more careful in future not to turn the “herbs” up too much. That should have probably been the end of the story, but I couldn’t resist siliconchip.com.au getting my own back on the manager. I had just bought a huge Circuits Manual from the USA, and as I was browsing through it, I saw something exciting. It was billed as a solid-state variac replacement; just what I needed, I thought! The circuit showed a power controller consisting of a UJT firing circuit and an SCR. It was said to be capable of controlling resistive loads of any current, limited only by the SCR rating. I soon had the parts and shortly after, had a breadboard version working. Of course, it was much smaller and cheaper than a variac, and I soon had a few prototypes out in some of the labs. The guys seemed to like them, but they had a few teething problems. They had terrible hysteresis, which meant that as you reduced the power level, they would suddenly turn off and to get them to fire again, you had to turn up the power way past the point where you were before. The guys naturally didn’t like this, especially as they weren’t sure what was happening. Later versions used a quadrac, which was a new device consisting of a Triac with an integrated Diac. The manufacturers even helpfully included a low-hysteresis firing circuit and RFI filter on the data sheet. It wasn’t long before we had the device perfected, and the researchers were all ordering them to replace their variacs. All went well for about six months until one day, the stores manager bailed me up after morning tea and said: “If you still want that variac, I have just received an order of a dozen so you can have one!” siliconchip.com.au The look on his face was priceless when I said: “Oh, we don’t use those any more. They’re old hat now. I’ve replaced them all with solid-state power controllers!” At least he would not have stock problems any more! Clenergy 1.5kW solar inverter repair R. S., of Fig Tree Pocket, Qld, got sick of having to get his solar inverter replaced under warranty. So he decided to try to fix it himself, with some success... The Clenergy SPH15 1.5kW solar inverter was supplied by Origin Energy as part of their low-cost solar power system. These inverters started giving an “Output Relay Failure” message after a few years. Mine was replaced twice due to this fault. I can see that the inverter boards now have external diodes placed across the relay coils, so it appears that the relay drivers were being destroyed by back-EMF from the coils. This must have been costly, with so many units replaced. A new problem is now occurring, with messages such as “GFCI Fault”, indicating leakage current to ground from the solar panels. However, megger testing of the panels shows no leakage. It seems that the currents on the DC inputs (from the solar panel) are being compared and the error is displayed if an imbalance is detected. There are two current transformers on the main board, one on the positive input and one on the negative input. There is a buck-boost converter immediately after the input, with two IGBTs Australia’s electronics magazine in parallel and a large rectifier. The IGBTs are driven by an ICC2818 controller, optically coupled via a TLP350 Mosfet/IGBT driver for isolation (see photo directly below). As current transformers need current pulses to produce an output, I thought that the buck-boost converter might not be operating. I have had problems with optically coupled isolators in the past gradually failing due to either low output from the internal LED and/or low sensitivity of the optical receiver. So I replaced the TLP350, and the inverter started working again. The GFCI fault disappeared. I am wondering how many of these inverters have been scrapped due to these problems. Be careful when working on these inverters, as the large high voltage capacitors take a long time to discharge. The low voltages are also supplied from these capacitors, so be sure that these are not present when working on the control section. I notice that to reset the display board, it is sometimes necessary to disconnect and then reconnect the ribbon cable. This is because the supply voltages persist, as described above. Since I repaired my inverter, a new error message is now showing: “Ground I Fault”. This has stopped the inverter working again. I will investigate this, but it will take some time as there are no circuit diagrams available. The only hope I have is to compare the operation of a working unit with the faulty one. It seems to be a fault on the main board, as swapping display boards does not make the error go away. SC May 2021  101