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SERVICEMAN'S LOG Trying to fix unbranded, generic equipment Dave Thompson The first step in sourcing spare parts for a faulty piece of equipment is to take the manufacturer and model details and do some searching to find out if the manufacturer or a third party has spare parts available. But what do you do when there is no apparent manufacturer or model number? Go on a wild goose chase, it seems... Items Covered This Month Sometimes a job comes through the replacement tyre took many months to workshop that is a bit out of left-field. I’ll take a look at anything; if nothing else, it’s all experience. Recently, I received a call about an electric scooter that had failed. This was one of these ‘friend of a client’ type deals, and I, for one, appreciate such referrals. In business, getting work this way sure beats paying for expensive advertising. This ‘scooter’ was a cheap import. While this doesn’t necessarily indicate that it will be a tricky job, I’ve been down this path too many times before to assume it will be an easy repair. According to the customer, in the 18 months they’ve owned it, the thing has spent more time off the road than on it. The tyres were the first problem, with the rear tyre blowing early on. It was apparently paperthin and not fit for our rough roads. A siliconchip.com.au source, and had to come from Europe. Not an auspicious start! Then it simply stopped working. The owner brought the scooter into my workshop, and after the usual discussions about terms and conditions and possible outcomes, I dug into it. This isn’t one of those thin-line electric scooters you see hipsters riding all over town on. This model is about the size of those mini-bikes Honda used to make back in the 70s, before the powers-that-be decided they were too dangerous for the average citizen. Australia’s electronics magazine • Fixing generic equipment is • • • • frustrating Arlec battery charger repair Fixing a 50in Panasonic TV backlight Failing capacitor in clothes iron Mazda 3 aircon repair *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz June 2021  91 It has fat little 10-inch wheels, proper mudguards, apehanger handlebars and a comfortable padded seat. It’s more like a small electric motorbike than a scooter. The various controls also mimic a motorbike; a twist throttle and front brake handle on the right, with back brakes on the left grip. It has a headlight of sorts, a taillight, and a sturdy kickstand. It is driven by a brushless electric motor integrated into the rear wheel hub. A standard key lock switches it on and off, and a small electronic display on the bars indicate the juice remaining and some other telemetry I haven’t been able to determine yet. I know the display can show other items because if I angle it to the light, I can see several other ‘icons’. My guess is that this is a generic display and is used on many other devices. This one is just wired to show the rider whatever information this manufacturer wants us to know. It’s all actually quite solid and well-made, but while it’s a step up from those rental scooters, it isn’t really a motorbike either. Still, it suited the owner’s requirements of buzzing a relatively short distance to work and back each day in relative comfort. Or would if it was working, anyway. I would love to have a ride on it, being an avid motorbike rider myself (though not for a few years now), but unfortunately, it wouldn’t move under its own steam. While it powered on and the battery bar-graph style indicator on the handlebars showed plenty of herbs, twisting the grip did nothing. All the other electrics worked, which was a good sign. Also, the guy (a skilled retired avionics engineer) who referred this client to me had ‘run his Fluke’ over it, looking for things that could potentially go wrong, but he had not found anything obvious. He did re-terminate some of the connections to the controller in case there was something dodgy there, but the problem remained. He figured it must be either a controller or motor fault, at which point he recommended that the owner bring it all to me. it isn’t all potted together with impenetrable goo, and the numbers are still left on all the components, I likely won’t find a circuit diagram for it anywhere. Reverse engineering the controller to draw one up would take hours of headaches and all with no guarantee anything would work anyway. What fun the serviceman’s life can be! I then went with basic specs. I know the battery is a 48V Li-ion job, and it is easily removed after unplugging the single heavy-duty ‘E’ connector. The battery at least has all the specs printed on a label. Nothing else is identified, though. The wiring to and from the various bits and bobs looks to be colour-coded, though whether this code matches anything else remained to be seen. The controller box also appears quite well-made, from the outside at least. It is a sizeable chunk of hollow, extruded and patterned aluminium, with what appears to be integral heatsinking along one side. It has shaped aluminium caps screwed on at each end, using what appear to be ordinary PK screws. All the cables pass through sealed holes in one end of the controller, and the whole caboodle is stuffed into a protected gap in the chassis, along with the battery, below the seat and foot-well area. A key-operated moulded plastic panel covers it all up, and there are basic weather seals along all exposed joints. The controller must be at least partially working, because if we insert the key and turn it on, we get the battery-level indicators on the dash, and the lights and other stuff works. If the motor had simply burned out, we would get the same symptoms – lights but no action. It is also possible that the motor-driver section of the controller has failed, but the rest of it is still working. A frustrating search After confirming the symptoms described above, the next step was to try to identify this vehicle. It has no brand name printed on it, nor does it have any part or serial numbers anywhere. Par for the course. A Google image search picked up a few similar bikes, available from the likes of eBay, AliExpress and Banggood, but nothing exactly like this one that could give me some clues as to its identity. The company it was purchased from 18 months ago were of little help either, having no spares available. My guess is that this is a generic bike, with various companies using the chassis, controllers and other bits and pieces to make ‘their’ version of it. They then sell them all off and move on to the next project. This has pros and cons for me; if the controls and hardware are generic, I should be able to find similar (if not necessarily identical) parts from any of these suppliers who sell such hardware. I’d have to drill a little deeper into the individual components and try to identify them. I know what you’re thinking; fat chance! Even if I can open the hefty extruded-aluminium controller box, and 92 Silicon Chip Australia’s electronics magazine siliconchip.com.au Opening up the controller So opening the controller up was my next step. Removing the controller is a bit of an act, because there are terminals and wiring going everywhere. There are four quite heavy-duty main drive cables coming from the controller, and these terminate onto posts moulded into a large hard-plastic block that keeps them all physically and electrically separated, but close together in the same area. These connections need to be undone with a socket driver. The other wiring is generally a lighter gauge and utilises removable connectors (some installed by my friend, some that look factory), making removing the controller relatively straightforward. The problem with the motor being potentially unserviceable is that I can’t easily test it. It is a brushless type, so it needs a suitable controller to make it work. Just connecting it directly up to the battery isn’t going to make it go, and in fact, would likely damage it. Except for the different type of motor, this whole job reminded me of a treadmill I repaired a while back. That too powered on and showed lights, but had no motor drive. The treadmill used a 12-130V DC motor, and I tested this by hooking up a car battery to the motor’s red and black wires. While it moved slowly at 12V, it at least worked, which told me it was probably OK and the controller had likely failed. That unit was ‘simply’ a DC speed controller; altering the power level to the motor increased and decreased its speed. These (for me, at least) are a bit easier to troubleshoot. In that instance, I replaced all the IGBT output devices (which were blown), but I also sourced a new controller board, just in case my repair failed. That repair worked, so at least I now have a spare controller in case it goes again. There were more differences between that job and this one, though. That board had part and model numbers clearly printed on it, making it a doddle to find a replacement. Perhaps I’d be lucky here too? With the controller sitting on the bench, I could more easily remove the end caps and see if I could extract the PCB from the interior. One long side of the board is taken up with an array of what appear to be Mosfets, or perhaps IGBTs. These all bolt directly to a piece of bar aluminium, and then this is bolted to one side of the controller case with a smear of heatsink compound and four bolts. These four bolts also had to be removed before I could slide the board free. Once all the fasteners were out, the board came out without any problems. The first thing I noticed was how light-weight the componentry looked. That treadmill controller I worked on was a hefty beast with a large external heatsink, and it was mounted away from everything with lots of room for cooling air. This little brushless driver, which admittedly only has to cope with 48V, must be quite efficient given the small size of everything. Or, perhaps it is built down to a price, underrated and too weenie for the size of the battery involved, which might also explain why it isn’t working. No obvious problems A closer inspection revealed no burning, discolouration, overheated rails or any other obvious damage to the board. There was also none of that acrid ‘electrical’ smell siliconchip.com.au Australia’s electronics magazine June 2021  93 we’re all so familiar with that usually indicates something is wrong. I didn’t fancy pulling the very closely-packed output transistors to test each one, so I made do with trying to find part or model numbers I could cross-reference. Nothing. And while some components (quite a few SMDs and the like) did have visible numbers, a lot didn’t either. If I could find a data sheet for the numbered ICs, there might be a reference circuit I could check out. Either way, I was stuck; I needed a known-good controller to test the motor, or a known-good motor to test the controller. Back to Google image searching. After trying various search terms, I began to see some familiar results. I found plenty of controller boards, but none looked exactly like this one. There were also many different types, with seven, nine and sometimes 12 output devices for the various sizes and voltages of scooters, bikes and batteries. I had a lot better luck looking for the entire controller itself. While it also has no identifying labels, it did look very similar to many of the image search results. I narrowed things down until I had pages of almost identical controllers in the results. The cabling on each was one of the few visible differences between them, with the controllers shown mainly having one of three different configurations. The controller I had looked to be a widespread type, which was a welcome discovery. Another difference was the physical size; controllers for 72V systems are far larger than their 48V counterparts, so again, I could drill further down into what I was looking for. The surprising thing is that I was expecting that even if I found one, the controller would be stupidly expensive. That treadmill controller was almost (but not quite) prohibitively expensive, though I deemed it worth it at the time to get one. The controller I found for the scooter is from AliExpress and costs just US$25, plus a couple of bucks shipping. I was gobsmacked. How can these devices be made for such little money? The fancy piece of aluminium extrusion it is all contained in must be worth more than that by itself. There were a few sub-types listed, so I ordered the version intended for a 48V electric vehicle with a brushless motor. It looked to have identical connections and overall physical size to the one I already had. Hopefully, what arrives will be what was in the product pictures; more than once, I’ve purchased items from the product description and received something very different. If all goes well, it will at least help me determine whether the controller or the motor is causing problems, and the negligible cost can be wrapped up into the assessment phase of the job without significant financial outlay. It is undoubtedly cheaper than sourcing and buying a new motor/hub assembly – which we might yet need to do – but for now, it will tell us all we need to know without throwing good money after bad. At the time of writing, I’m still waiting for the controller to arrive. Given current world events, it’s no surprise shipping is slow. I’ll let you know what happens. A happier ending In the meantime, I got a call from an out-of-town rep for a company that provides exercise equipment for gyms and retirement homes. He had a dead machine in one of their spaces down here and an open day the following day. He wanted me to make an assessment or repair (if possible) of the controller board, which he would remove and bring over, along with the external power supply. I agreed, and offered assistance if he needed it. He didn’t; the controller came out easily, and a fault was immediately apparent; a 47μF 35V SMD electrolytic capacitor had exploded. He brought the board to the workshop, and we agreed that I would swap out the cap. If it blew again straight away, he’d return the board to the manufacturer for a replacement and forgo the open day. I soldered in a new cap, and we held our breath while we powered up the board, watching as the status lights lit up one by one. His grin said it all. He went back, reinstalled the board, fired up the machine, and the open day was a success. Sometimes we just get lucky! Arlec battery charger repair B. C., of Dungog, NSW took some time to refurbish an old Arlec battery charger that had seen some rough use, but it is now back into tip-top condition... I got an Arlec PS439 30 Deluxe Battery Charger from the local recyclers which wasn’t working. Also, the top cover was in pretty rough condition; it looked like it may have spent its former life at a local motor garage. My friend said he would clean it up and respray 94 Silicon Chip Australia’s electronics magazine siliconchip.com.au the top after I got it working. Removing this cover revealed an accumulation of debris and also some corrosion on the power transformer, heatsinks and the control PCB. Careful use of a toothbrush, paintbrush and solvent cleaned up most of the mess. Scraping, followed by an application of rust converter cleaned up the power transformer laminations. Fortunately, the front panel with the ammeter, timer and switches had been protected by the overhang of the top cover, and only required light cleaning. I was then able to greatly improve its external appearance using Nu Finish car polish on the case paintwork. I then sent a technical request email to Arlec in Melbourne and received back two circuit diagrams, a control PCB layout drawing and a “current-control switch connections” drawing. Interestingly, the drawings were all done in 1983. Talk about the thorough technical support for Australian made products! This battery charger was a wellmanufactured product and was meant to be foolproof to use. The charger would only work if the battery had some residual charge left in it and the connection polarity was correct. There are now plenty of modern chargers that use a similar system. Looking at the circuit diagram, I discovered that there are two main high-current secondary windings on the power transformer. A rocker switch selects the voltage to feed through a rectifier block to charge either a 6V or 12V lead-acid battery. A large rotary switch is then used to switch through a series of voltage taps to give current siliconchip.com.au control of the output, as displayed on the ammeter. A timer gives the user a preset charging time, to avoid battery overcharging, particularly on the higher current settings. There is also an extra transformer winding which gives a regulated 12V rail to run the control PCB electronics. After some basic voltage checks, I traced the fault to a lack of 12V at the output of the series regulator. This was because the TIP31C transistor (mounted on a small heatsink) was faulty. I also found that the BZX79C13 13V 0.5W zener diode controlling the voltage at the TIP31C base had gone short-circuit. Replacing these two parts brought the Arlec charger back to life. I then connected it to a partially charged car battery and set the timer to complete the charging cycle. As promised, my friend resprayed the top cover to match the orange enamel finish of the chassis. This charger now sits proudly on a trolley in his garage. Fixing the backlight in a 50in TV P. M. of Christchurch, NZ, had a badly-timed failure in a 50-inch LCD TV. Luckily, he has quite a bit of TV repair experience, so was able to tackle the job... As New Zealand was under “lockdown”, all businesses except essential services were closed, and everyone was told to stay at home. This meant that the home TV had become an essential entertainment and information device. Two days in, and suddenly our Panasonic 50in LCD in the lounge had Australia’s electronics magazine no picture. I have been trained to service TVs, but that was many decades ago when TVs had CRTs. But it looked like I had little choice under the circumstances, and attempted a repair. I soon had the beast off the wall and face-down on the kitchen table. I removed the back, hoping to find some sick-looking electrolytic capacitors which I could easily replace. I was surprised to see how few electros there were. None of them looked sick, and all tested OK with my ESR meter. I was surprised at how sparse the interior was, with a power supply board in the middle, a small video board on the right, a backlight driver board on the left and a display driver board at the bottom. The power supply rails all looked good, but I was not so sure about the backlight driver outputs. I managed to find a manual online, but the driver board was mainly SMD, and I didn’t have high hopes about being able to fix anything. In the meantime, I put a 32in Panasonic from another room on the wall in the lounge. After a day or so of squinting at it, I decided to have another look at the 50in set. Inside it, I noticed a label saying the display was made by LG. I Googled ‘repair 50” LG TV’ and found several hits on replacing the backlight LEDs. It seems this is a common problem with some models, made worse if the user chooses a high brightness setting. Gaining access to the backlight LEDs involves removing the LCD panel from the housing. In the Youtube video (https://youtu.be/CHmHb-Dxx3Y), the repairman used two suction cups June 2021  95 attached to the front of the panel to lift it out. Not having those suction cups meant I probably couldn’t continue, but then I remembered that we have a handle in our shower which is held on with suction cups (as shown in the photo at lower left). This handle was not ideal because the cups are quite close together, unlike the separate ones used in the video. I attached it carefully to the screen after removing the bezel, a bunch of screws and two flat ribbon cables. When I started lifting it, the panel got a bit bendy at the ends, but I managed to set it down safely. There are three sheets of Mylar that act as a diffuser to remove, and beneath those are six rows of 10 LEDs (as shown in the photo on page 95). The LEDs are on strips of circuit board which plug into a connecting circuit board at the right-hand end. They are wired in series, so with the aid of my bench power supply set to 30V at 20mA, I was able to power each strip separately, to find that two strips did not work. Upon closer inspection, I noticed a discoloured LED on one strip but I had to find the faulty one on the other strip with the aid of a meter. Not having suitable replacements on hand, I decided to simply short out the two faulty LEDs, and because they are wired as two strings of thirty, it would probably still work fine. I carefully reassembled everything and held my breath while I switched it on. It worked just fine, and the only time you could tell two LEDs are missing is on a pure white screen. Even then, it is not that obvious. The YouTube video had a link to a store which sells a full set of replacement strips for US$60, so I will order a set when I can. The heatless clothes iron R. S. of Fig Tree Pocket, Qld, had a problem which has been repeated many times over the last few years in these columns. You may get a sense of deja vu while reading it... Our Braun clothes iron stopped heating. It was more than two years old, so already out of warranty. If you take the grey rubber pad out of the end of the iron, you can undo two T20 ‘security’ screws. This allows the end to come off, and there is a black plastic box with a small circuit board inside. It contains an unmarked surface-mount 96 Silicon Chip 8-pin IC with its supply regulated by a 5V zener. The low-voltage supply from the mains is via a 220nF 220V AC rated X2 capacitor and a resistor. The capacitor tested OK using the capacitance range on a Fluke 77 IV multimeter, but I replaced it with another 220nF X2 capacitor, and the iron now works. It seems that the capacitance is lower at high voltages. I note that the replacement capacitor was many times the size of the original. This is another example of highvoltage series capacitor failure. I notice that the inverters in microwave ovens use a high-wattage resistor to drop the voltage for the control circuit. This is more reliable, but with a higher power loss. Mazda 3 aircon repair D. W., of Georges Hall thought his daughter’s car might have had a serious malfunction buried deep within, but luckily, it turned out to be a much simpler (and cheaper) fault than originally envisaged… My daughter told me that the air conditioner in her 2008 Mazda 3 was playing up. It didn’t work straight away; the car had to be running for about 15 minutes before it would produce cold air. Up close to the front of the car, I could hear a strange noise from under the bonnet somewhere. It sounded like it could have been a compressor belt or clutch problem. Maybe one or the other was slipping a bit, but then it eventually grabbed. That might explain the delayed turn-on. Maybe the belt had stretched or worse, the compressor could be on its way out. A faulty compressor would probably be a costly fix. That night, I found myself on YouTube searching for Mazda 3 aircon compressor faults and fixes. Sure enough, there were a couple of detailed and somewhat educational video clips depicting Mazda 3 compressor and clutch faults and fixes. A couple of days later, my daughter brought her car over, and I had a bit more time to look at the problem. Thanks to the YouTube video clip, I knew where to look for the compressor. The noise I had heard previously wasn’t evident on this occasion. Turning the aircon on and off and watching the compressor belt and clutch didn’t reveal anything unusual to my eye. Australia’s electronics magazine I noticed a slight coating of frost on one of the compressor pipes, so I thought that the compressor must be doing its job. I was now getting that feeling that I’d missed something. While sitting in the car operating the controls and mulling over things, it suddenly dawned on me that there was no airflow from the outlets in the car. Regardless of all else, there should be airflow. The fan control knob appeared to be working OK as the dash LCD was indicating the different fan speeds. So it was not a compressor belt or clutch problem; it was a fan blower problem. Not for the first time, my brain had led me up the garden path. So I headed back to YouTube for more advice. YouTube has a lot of video clips on Mazda 3 fan blowers. Unfortunately, everything is located up behind the glove box, and it’s hard to get to the fan assembly. I realised that since the blower fan does come on after a delay, the fan itself must be OK. So I had to think of what else might be causing this problem. I checked the 40A blower fuse (marked heater) and it was OK. Next, I pulled out the small quick-connect blower relay (also marked heater) close to the fan blower fuse and tested it on the bench with a 12V power supply and multimeter. And that was it! I could hear the relay clicking in and out, but the contacts were simply not closing. It was easy enough to lever off the relay’s dust cover and inspect the SPST contacts. I set about cleaning the contacts with wet and dry and contact cleaner but surprisingly, to no avail. While testing the relay, I could feel the relay getting warm while energised, and after about 15 minutes just sitting on the bench, the contacts eventually closed, as if by magic. I think heat and fatigue over the years had affected the spring steel relay contact arm. As a temporary fix, I bent the arm a fraction of a millimetre to close the gap a bit. After replacing the dust cover and returning the relay to the car, the problem had obviously been licked. I’ll source a new relay in due course, and I’m still a little worried about that noise I heard initially, but hopefully it was just the blower fan operating erratically with its control relay making dodgy contact. Time will tell. SC siliconchip.com.au