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SERVICEMAN’S LOG Computer abuse Dave Thompson As most of you probably know, I don’t write much about my day job, ‘fixing’ computers. Not because you wouldn’t be able to handle the dramatic highs and lows of such a high-octane job; it is completely the opposite. You’d be bored to tears for the vast majority of it. Still, now and then, something comes through the workshop that leaves me speechless! N owadays, most 10-year-old kids can fix the things that usually go wrong with computers. Modern software and children now handle what was once a very specialised field. Most of the time, it is mundane, with the odd curly problem thrown in to make things a tiny bit more interesting. Of course, those rare wins can be very satisfying, even though they are few and far between. More often than not, they are tempered by having to break the bad news to someone who has lost their data, or simply their machine, because it has reached the end of its useful life. It doesn’t help that most computers are now designed to last for a couple of years, then die, with all their memories lost, like tears in rain (cue the heart-rending speech from Blade Runner). Most tablets and laptops these days work fine for a while, then suddenly quit, or in the case of laptops (pun intended!), they physically break because the chassis and frames are made so thin in an effort to ‘add lightness’. With many machines, simply opening and closing them a few times a day – what I’d call ‘normal use’ for a laptop – will soon break them. The other issue with many portable computers is the power socket. On tablets, this is typically a micro-USB or a USB-C connector. On laptops, it will often be something proprietary, especially in the case of Dell machines, or something more familiar like that used in most Acers. Over the years, I have repaired hundreds of power sockets because they are so easily broken. We’ve likely all picked up a device by mistake that is still plugged in and put strain on the cable, or tripped over the cable laying across the floor to the nearest power point and sent the machine flying! The resulting leverage on some of the connections is considerable due to the size of the plugs and leads, and it is no wonder that sometimes the sockets get torn from the motherboard. However, that was not the real problem with a machine that came into my workshop recently. I repaired the power 86 Silicon Chip socket on this one a year ago, but it came adrift again. The client swears it hadn’t been dropped or mistreated, but as their dad literally had to bolt the screen back on, I had some questions. I don’t think I have seen a laptop in such a poor state, and I’ve seen a few! Young people these days... An adolescent owned this machine, and in my experience, they don’t tend to look after their tech (or other possessions) very well. The number of units that come through the workshop that are scarred from schoolyard use has increased over the years. Many schools now demand that students have tablets or laptops, often dictating which make and model they should bring to school. Usually, this is an iPad or iMac, among the most expensive tech you can buy. One wonders if the schools get a kickback on these sales, as they used to do when Apples were first introduced into schools in the 1980s. When I was at school, not quite the chalkboard days, we had to have a certain number and style of books. I remember standing in line waiting with a list of requirements as we all filed past stacks of exercise books of all descriptions. This, of course, carried on into universities, where students must buy reference books, usually written by professors there, to pass their classes. That’s a rort in itself, but a subject for another forum! So now most schools tell students they must have this Australia's electronics magazine siliconchip.com.au Items Covered This Month • Stress testing your electronics • Using a chlorinator for rust removal • Repairing a 27A switch-mode battery charger • Fixing an LG42LD460 TV power supply unit • Repairing WiFi-controlled LEDs Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Cartoonist – Louis Decrevel Website: loueee.com or that tablet or laptop. While Chromebooks are popular in some schools (and are at least reasonably cheap to replace when they are inevitably broken), most of the more prestigious schools require expensive makes and models. That is all well and good, but give a 13-year-old kid a tablet or laptop, and we know they are going to chuck that thing around, no matter how much it costs. I’ve seen many almost-new devices with broken screens, dented corners, drinks spilled down the keyboards, the usual stuff. This one was slightly different because I had already repaired the power socket once. If we do walk away with it plugged in when the lead runs out, the strain on the socket can wreck it. Whether it’s a micro-USB or USB-C charging port, as used in many phones and tablets, or one of the bigger sockets used on laptops, the result is often the same: breaking the socket, or some of it, or tearing it off the PCB inside the machine. These sockets are often held onto the board only by the soldered joints and perhaps a few Earthing tags. As those in phones and tablets are usually surface-mounted, there really isn’t much holding them to the board. Solder is not glue; it is inherently weak. If we’re lucky, four tiny fingers of metal extending from the socket case go through four corresponding holes in the ground plane on the PCB. Still, many of these sockets are just spot-glued with some type of component cement before being soldered in a bath or reflow oven. There is virtually no strength in that glue or connections, and in the scenario of walking off with it plugged in, often the socket is torn from the PCB. In many cases, a few of the PCB tracks go along with it. Getting inside the device Over the years, I have replaced hundreds of these sockets in phones, tablets and laptops. The main difficulty is that modern devices no longer have a back that can be popped off to reveal the screws that must be removed to access the ‘logic’ board. Almost all phones and tablets now require going in through the screen, which automatically makes them infeasible to repair, even if you have a hotplate for loosening the glue on the screen. Most screens are now so thin that even a slight twist will crack them, and new screens are often prohibitively expensive, if you can even get one! At least most modern laptops are easy enough to get apart, held together by about a dozen same-sized screws and some easily ‘poppable’ plastic clips. The whole bottom siliconchip.com.au (or top) typically comes away with just a few ribbon cables connecting the keyboard or touchpad to free up. It is nothing like olden-day devices that had tons of hidden screws of all weird sizes, which were often buried under the keyboard and even under the rubber bumper ‘feet’ on the bottom, which had to be pried loose to access the screws. Of course, they had to be stuck back down with new tape when it was all reassembled. The worst of those I can recall had a long, thin strip of rubber running the length of the machine, acting as a single long ‘foot’, which invariably tore when trying to remove it. Fun and games for computer techs back then! Returning to the laptop in question So, back to this one on the bench. As mentioned, I have repaired its power socket before. While not old, the computer has had a very tough life. Usually, when I repair one of these sockets, the repair lasts for the life of the machine because I use epoxy resin to bolster the strength of the socket once I’m sure it is all reconnected and working correctly. One has to be careful doing this because there is not a lot of room in these things, and it pays to make sure the top (or bottom) cover will fit on once a fillet of rock-hard glue is added around the socket! I don’t know how this current damage was done – the kid assured the parents that she’d not been rough with it, but the fact remained that the socket and motherboard were once again rendered asunder. I could feel it floating around in there when I probed it with one of my dental picks. Opening it up was interesting, because most of the plastic that made up two of the corners, where the hinges for the screen usually live, was simply not there. The screen itself had a diagonal crack in the top-left corner. I don’t think I could damage a machine that badly if I tried! The screen frame had popped open, and the clips that are usually there were missing in action, possibly floating around the back of the panel somewhere. The most obvious hint that something was amiss is that the husband had broken out his DIY skills: he had drilled out and held the righthand hinge and screen together with two nuts and bolts, which he likely got from the local hardware store. I thought I had pretty much seen everything over the past 25 years of doing this job, but I haven’t seen a post-­industrial repair like this before! Australia's electronics magazine July 2024  87 That said, the repair he had made was quite sound. I have no idea how he missed the LCD panel while drilling the two holes; it was likely pure luck. If he’d touched even the frame of it with the drill bit, it likely would have put yet another crack in the screen, and if he had gone through one of the ribbon cables or connectors, it would have been game over, man, game over! In the above photo, you can also see the black-and-white WiFi antenna wires, which are ultra-fine shielded cables that usually wrap around the edges of the panel, ending up at the top, on either side of the camera. In this case, the black one should be wrapped around the left-hand side of the panel, instead it is hanging in the breeze through the broken hinge section on the right side. Both of these wires start on a removable/replaceable module on the motherboard and are routed through channels designed for them, then pass through the lid hinge’s normally enclosed cavities into the frame around the screen. Not any more; on this side, the black lead has been bundled with the white lead, and the white wire has been severed almost at the hinge area; it simply pokes out into space. I imagine this would compromise the WiFi performance, but I have seen machines perform quite well before with those wires wholly disconnected from the module. That can happen when a tech has neglected to replace the tiny coax plugs at the ends of these cables onto their tiny sockets. On older machines, to get the motherboard out, I often had to take the WiFi module out, as it was fouling on the chassis, and in some cases formed part of the motherboard support structure due to it being screwed into place. Those antenna leads must be routed into their channels and reconnected during reassembly. If the user is close enough to the router, it would still work, but the operating range would be much shorter. It certainly isn’t ideal to have one poking out the side of the machine! So, the hinges are compromised on both sides, although only the right side has been fixed with bolts from the shed. The left hinge floats in the broken panel frame; the little metal inserts in the plastic turrets that usually support the hinge screws have all broken away and are sitting on the screws still attached to the hinge. This was looking increasingly pointless to repair, and I hadn’t even gotten to the motherboard yet. 88 Silicon Chip Disassembling the case wasn’t as difficult as I thought it might be because most of the screws weren’t holding onto anything anyway! Most of the clips that usually kept things nicely flush had sheared off, so it was simply a matter of getting a spudger (in this case, a guitar pick I use to open cases) and going around the edges to see what would come apart. A few of the screws still bit into their threads and held the case together, so I removed those. The bottom came away cleanly and I could clearly see the power socket floating loose in the recess that usually helped locate it. The plastic surround that helped support it had broken away last time, and I could see that some of the epoxy resin was still where I’d put it, except that the socket had broken out of it. There must have been a lot of force because that stuff is pretty tough, especially when it has lots of nooks, crannies and surface area to grab hold of. Given that the plug on the power supply was bent at a crazy angle, someone had really yanked on it to cause this much damage! I fished the socket out and could see it had torn the connections from the back of the socket. It had also taken some of the corresponding PCB tracks off the motherboard; there was nothing left there to solder anything to. With the previous repair, I could at least resolder the socket before testing and gluing it in place, but now, a new motherboard was the only real option. The glue I had added previously had also torn some tracks as part of it broke away, making even more of a mess. Maybe it wasn’t such a good idea after all, gluing it on, but I have done dozens of repairs like this over the years, and to the best of my knowledge, all those repairs lasted for the laptops’ natural lives. This one is an anomaly; the sort of damage I’m looking at can only be caused by gross mishandling or perhaps being thrown in a tantrum or similar. I didn’t ask; all I was told was that the daughter assured her dad she hadn’t dropped it. Maybe she was using it as a cricket bat! I don’t know, but I’ve seen less damage from machines that have fallen down the stairs or have been run over. I went through the motions of trying to source a ‘new’ motherboard, but the best I could do was a ‘refurbished’ one out of China. The last one I bought from sources there Australia's electronics magazine siliconchip.com.au didn’t work on arrival, and I took a big hit on that, so I wasn’t keen. Given that the rest of it was in such dire shape, I made the call to the dad and told him the bad news. He was philosophical about it, likely envisaging having to buy a new device for his daughter so that the same thing could happen to it. Parenting is tough, I guess! I put it back together as best I could, and they duly came and picked it up, the daughter looking suitably sad and sorry. I gave them the good news that her data was all there, so I could easily transfer it when they got a new one. I didn’t have the heart to charge them after returning the wreckage. Repurposing a pool chlorinator I spotted a couple of pool chlorinators on a recent visit to the local tip shop. One was pretty beaten up, but the other was in good condition, apart from having the power cable cut off. I decided to grab the better one of the two, as I’ve been using one of these units for my electrolytic rust removal bin for several years, and it would be handy to have a spare. When we got home, I put it away and didn’t think any more about it. About a week later, my pool chlorinator stopped working. On disconnecting it, I noticed that one of the front panel LEDs flashed. Investigating further, I found that the 35A bridge rectifier had failed. I have spare rectifiers, but I decided to check out the “new” one to see if it worked. If it did, I’d put it into service instead of repairing the one I had been using. I could see why the power cable had been cut off; the outlet socket on the bottom of the unit was broken, exposing live terminals. The first thing I did was to remove the outlet socket and rewire the unit to bypass it and the timer, which I didn’t need anyway. I then fitted a new power cable and plugged it in. The ‘No Water Flow’ LED lit up, indicating that the unit most likely worked. The unit has two heavy output leads, one for positive and one for negative, plus a thin wire for water flow monitoring. I connected the thin wire to the negative terminal, and the unit then started pulsating. That was unusual, but it was likely because it didn’t have a load. siliconchip.com.au I connected it to the rust removal bin, the pulsating stopped and the Chlorine Output meter showed that the unit was working. It could be adjusted by turning the output control. The old chlorinator has a 9V 20A transformer, which I could always use for something else. The replacement unit has a 9V 27.8A transformer and two bridge rectifiers instead of the one in the old unit. So this unit is more powerful than the old one. I made two plates, then pop riveted one over the hole where the timer had been and the other over the hole where the outlet socket had been. That made it ready for use. I have been using electrolytic rust removal for several years. It is very handy for cleaning up rusty tools and other items but only works on ferrous metals. Once, I picked up a 6-inch vise at the tip shop that was totally seized. After three days of treatment, I got it apart, and another three days later, it was cleaned up and I could paint it and use it. B. P., Dundathu, Qld Editor’s note: for information on the process, see our article in October 2014 (siliconchip.au/Article/8041). Australia's electronics magazine July 2024  89 Switch-mode battery charger repair This Innovative Energies SR750-24 charger converts its 230V AC input to 27.5V DC at up to 27A. The charger had not been used for some years, so its failure was not a great surprise. I agreed to see if it could be repaired, but an online search showed that it was a legacy item and quite a few years old, so spare parts supply could be difficult to obtain. With some degree of trepidation, I took possession of the charger, which was not easy to carry as it weighed 5kg and measured 350 × 200 × 75mm. Removing six small screws allowed the cover to be lifted off and the reason for the weight became apparent – it was fitted with two massive internal aluminium heatsinks and four large coils (chokes and/or transformers). The probable main reason for the failure was also immediately obvious: two 0.68µF 275V AC WIMA capacitors had ‘spilt their guts’ of the insulating oil contained within, which was spread all over the main PCB in their immediate area. I considered that the oil could contain nasties, so I kept my bare hands away from it. This PCB area included several small common components and ICs. Later investigation revealed this circuitry was in the charger voltage and/or current control. The first problem was removing the main PCB from its case to access these capacitors’ solder side. That turned out to be quite simple, as the mains input wired connections and the output DC connections are easily pulled off PCB-mounted spade connectors. Then, after undoing eight small screws, the PCB lifts straight out. This revealed that each of these capacitors was wired in series with the incoming mains Line and Neutral conductors, coming before several mains filter/noise suppression components. This also indicated that these capacitors were being used as simple AC voltage-dropping devices, so their capacitance values would not be particularly critical. As the series mains input 10A fuse was not blown, other major components had probably not failed. The high-­ voltage stress placed on these aged capacitors when the unit was switched on could explain their failure. The next step was to procure and fit replacement capacitors of similar size and specification to the original failed capacitors. The closest available value stocked by Jaycar was 1µF, so I fitted them temporarily (they have a 50Hz reactance value of 3.2kW versus 4.7kW for 680nF). I thought that was close enough for a go/no-go test. I cleaned the spilt oil off the PCB as much as possible before soldering in the new capacitors and reconnecting everything. While standing well clear, I switched the mains power on. This smoke test was successful as there was no smoke, no component appeared to overheating, the Charger Load display came on and the DC output measured about 27V. I subsequently connected the charger to a suitable 24V lead-acid battery and it charged the battery in the expected manner. After a further soak-test period, it was still operating. So, another electronic unit that would have cost a considerable sum to purchase in its day was saved from the scrap heap by about $5 of replacement parts. G. C., Wellington, NZ LG 42-inch LCD TV repair After a successful service of 15 years, my LG 42LD460 LCD TV failed. During the last cricket World Cup, hosted by India, the TV served flawlessly! However, I have been unable to switch it on for the last three weeks. The LG TV expert came and opened the back cover deftly. After a few tests, plugging in and out a few cables here and there, he Left: the failed SR750-24 battery charger. Right: the 42-inch LG LCD TV 90 Silicon Chip Australia's electronics magazine siliconchip.com.au joyfully declared that the power supply unit was beyond repair. When I asked for a replacement, he chuckled and, after a few calculations, revealed that it would cost me about INR 11000 ($200) for a replacement board and would take about a month to get. He said spending so much on repairing a 15-year-old TV was not a good idea when a new and better TV only cost about twice as much. After he left, I brought down the TV from the wall, opened the back cover and checked the power supply. I had to remove 16 screws to remove the back cover and found two boards, the TV motherboard on the left and the power supply on the right. The power supply has four connectors: the mains input, a ribbon cable to the motherboard and red and black wires supplying the backlight. While all the other cables came out easily, the ribbon cable gave me some trouble. I spread the locking fangs with a small screwdriver and it came out. The power supply board has a surface-mount fuse, which I knew the LG expert checked. I checked the first bridge rectifier of four diodes and it was OK. All the electrolytic capacitors seemed fine, with no bulging, and I didn’t see any blackened resistors. The rectified DC finally comes to a six-lead STR-W6053N IC, which converts it to lower DC voltages for the motherboard. The IC’s data sheet reveals that there is a feedback signal that comes from the TV motherboard through lots of circuits. If the motherboard does not produce the requisite feedback signal, the PSU will not work. Since the repairman said the power supply was dead, I removed it and took it to a local TV repairman. He told me that the TV is required; he can’t do anything without it. I asked him if he could visit my house to check the TV in situ as shifting a large TV is difficult! His answer was no. I searched the internet for TV replacement parts and found many shops that deal in TV spares, but couldn’t find my model listed. Frustrated, I rang one shop, and they quoted me around INR 4500 ($82) for a new power supply. I immediately placed an order and crossed my fingers! The power supply arrived four days later, neatly packed in a box. I opened the box and fitted the module into the TV. Nothing happened! It was still dead. Frustrated, I called the shop again and told them that the module seemed defective as the power supply was still not coming up. The man on the other end of the phone had a good knowledge of TVs. He asked me all the details of the fault: how it started, what the branded TV expert opined and my amateur repair process. He then told me that, in all probability, the TV motherboard was defective, not the power supply. He also informed me that he had seen many similar cases of incorrect diagnoses by the branded experts. He told me that I could return the power supply module and get a refund or buy a TV motherboard. If the power supply turned out to be OK, I could return it for a refund. Therefore, I end up coughing out another INR 5000 ($91) for a motherboard card. The card arrived in three days from Hyderabad. The motherboard card replacement is a little more delicate as it involves the removal of two flat ribbon cables, but they came out pretty easily (just open the lock...), and the new card was in place quickly. And the TV woke up after a slumber of 29 days! Before boxing up the TV, I tried siliconchip.com.au Australia's electronics magazine July 2024  91 the old power supply, and it also turned out to be working! So the TV motherboard card was the culprit all along. The power supply card has been returned for refund and the TV is still working well. At one point, I almost made up my mind to get a new TV as my wife was missing her daily serial shows. Only my persistent mind kept the hope of a successful repair alive. TV companies will always lure you into making new purchases by telling you that parts for older models are unavailable etc. But don’t get fooled. The old parts are available all over the internet. Search for them or even call them. They will certainly help you out because they also want to sell their goods! B. S., Kolkata, India Repairing a WiFi-controlled mains LED light I purchased several WiFi-­enabled ‘smart’ ceiling lights from Bunnings a while ago. A nifty app allowed me to change the brightness and colour temperature using a smartphone. While that was great in theory, we found that we typically set the colour and brightness once and then, around 99% of the time, simply used the light switch to turn them on or off when needed, as these lights were in our dining room and TV area, not in a bedroom. However, these clever lights proved highly unreliable. Two out of four failed and, as is the norm these days, it happened just after the warranty expired. Initially, they only partially failed, refusing to respond to WiFi commands but still turning on via the light switch at a usable brightness. So, we tolerated this unfortunate failure and continued using them as ‘dumb’ lights. Regrettably, after several months, both lights failed entirely within a few weeks of each other. Not wanting to spend a significant amount on a new light that would likely be just as unreliable, I decided to investigate whether they could be fixed. Removing the first light, I found that all the electronics were on a large PCB, which appeared to be made of ceramic or a similar material. Whatever it was made of, it was clearly designed to dissipate the heat produced by LEDs, and it did so very effectively. Due to its excellent heat conductivity, I had to use a much larger soldering iron tip than usual. I also noticed that the light’s white metal outer case acted as a heatsink, a necessary feature since excess heat is the leading cause of premature LED failure. 92 Silicon Chip Tracing the circuit proved extremely difficult due to the opaque ceramic substrate. However, the basic design quickly became apparent. The mains was converted to a current-limited 24V DC using a WS-LV24-G24L-L LED driver module. Next was a tiny SMD 5V switching regulator powering a TYWE3S 16-pin ESP8266 WiFi controller module, along with an unmarked microcontroller. Finally, a couple of Mosfets were used to drive the two banks of LEDs (daylight [5000K] and warm white [3000K]), with each Mosfet controlling a single bank. These two banks allowed the app to set the light’s colour temperature by adjusting the power ratio of the two LED banks. A multimeter confirmed that the 5V power rail was OK, measuring correctly at both the MPU and WiFi modules. Next, I measured each SMD resistor, and they were all within spec. I then unsoldered and tested each Mosfet, and they were also both OK. The fault must be in either the PCB tracks, the MPU or the WiFi module. However, it was virtually impossible to check the PCB without a circuit diagram due to its optically opaque substrate. It appeared impossible to replace the unmarked microcontroller without a part number or, more importantly, a way to obtain the firmware. The last suspect was the ESP8266 WiFi module, but a Google search showed only one hit for it worldwide, and it was nearly as expensive as a new ceiling light. So, it appeared that replacing any of these parts wasn’t a viable option. After some thought, I wondered if it was necessary for the WiFi feature to work. I could convert the lights to ‘dumb’ lights with just one or two resistors! As I prefer daylight white LED lighting, I only needed to solder one 5W, 10W resistor between the +24V supply and the daylight white LED bank, bypassing the Mosfet. If I preferred a more ‘warm’ light, I could have used two resistors, one for each LED bank, although the resistances might have needed to be increased to get the right final brightness. While not the most elegant solution, it converted the non-functional ‘smart’ lamps into functional ‘dumb’ lights controlled by a light switch. While it would have been more elegant to repair the WiFi functionality, this makeshift solution got both lights working for less than $2, which was much better than spending $150 to replace both with new smart LED light fixtures. SC G. C., Cameron Park, NSW Australia's electronics magazine siliconchip.com.au