Fullscreen HTML5Med Res (??MB)HTML4

SERVICEMAN’S LOG Repair and servicing stories from readers LED gym sign repair A friend rang and asked if I could take a look at his son’s gym sign; some letters were not lighting up correctly. He said they were willing to pay up to $300 for the repair. The sign duly arrived and I connected it up to its 12V, 15A power supply. I could see straight away that several letters had sections missing. The letters have a silicone moulding as a cover that could be easily removed to access them. I could then see the arrangement of the LEDs. They were 12V segments, all connected in parallel. Each segment had three LEDs and a series resistor, with copper pads at each end. The segments could be cut at the copper pads to get the required length. There were numerous faulty segments in each letter; the damage looked like it was from water ingress. The sign had been hanging outside the premises, supposedly under cover. There were 120 LEDs per meter, with some sections bright white, and some blue. I found similar LEDs on the internet and ordered a 5m roll of each colour, hoping that they would match the existing colours. Otherwise, I would have to replace the lot. When the LEDs arrived, I powered a section of each colour from my bench supply and saw that they matched the originals perfectly. Now it was just a matter of replacing the faulty segments. I removed the silicone moulding to access each area of LEDs, then cut out the faulty sections and used Kynar insulated wire-wrap wire to connect the new LEDs to the existing strips. It was quite a fiddly process, which took about five hours. I finally had to fit the silicone mouldings back into place and the sign was back to its original condition, with all letters now complete. I rang my friend, who was delighted that the sign could be used again, this time inside the gym. He asked how much he owed for the job. I was happy to get paid for the parts plus a bottle of scotch for my efforts. John Western, Hillarys, WA. A WiFi repeater and leaf blower My electronics workshop is in a shed behind our house, but the WiFi signal from the house is quite weak inside the workshop, so I’ve been using a WiFi repeater to boost the signal. It was powered via an extension lead under the covered walkway next to the workshop for a long time without any problems. Just recently, we had a big storm with torrential rain, and I didn’t go to my electronics workshop for several days 82 Silicon Chip because of the bad weather. When the rain finally eased, I went there to work on a laptop, but I found that the WiFi repeater was no longer working. I turned the power to the extension lead off and removed the device. It was wet; rain must have blown under the covered walkway, resulting in water getting into the repeater. I prised the two case sections apart and found that the power supply board was completely destroyed. There were components with sections of their leads missing and a lot of corrosion on the circuit board. I remembered that I had another one of these WiFi repeaters that no longer worked, but it was slightly different to the one I was using. I wondered whether I might be able to transplant the working WiFi board from this damaged unit into it. I separated the two case sections and found that the power supply board was completely different, but it had the same plug for the WiFi board. I removed the faulty WiFi board and installed the one from the destroyed unit, then I reassembled it with the original top. I plugged it into a power point to test it and the LEDs lit up. I plugged the WiFi repeater back into the extension lead and re-located it further under the covered walkway to better protect it from the weather. It often pays to hang onto non-working electronic equipment in case you need spare parts from it later. Bruce Pierson, Dundathu, Qld. Leaf blower charger repair (again) Following on from this, once again, I’ve had to repair our leaf blower charger. This time, the repair was not easy as the charger would work intermittently. Still, in the end, it’s finally fixed and working correctly again. Australia's electronics magazine siliconchip.com.au A close-up of the dry joints on the leaf blower charger PCB. When a flat battery is connected, the LED turns red, showing that the battery is being charged. The charger contains circuitry that controls the charging and switches the charger to standby when the battery is charged and the LED turns green. Recently, my wife said that the charger was not working; the LED was staying green when a flat battery was connected. I’d made two previous repairs to this charger. The first was when I had to replace the plug, and the second was when the insulation near the case was broken and the wires were shorting. As I’d already cracked the case open for the second repair and glued it back together with superglue, it was a little easier to crack it open again. I suspected bad capacitors, and in testing the two largest capacitors, they both showed a high ESR reading. The two smaller capacitors tested OK, so I thought they were still good. The capacitors were rated at 4.7µF 400V and 10µF 400V. I did not have either of these in stock, either salvaged or new, so I had to order them. These capacitors are much smaller than regular capacitors, and there is very limited room in the charger’s case. I had to check many listings before I could find the right sizes to order. The capacitors arrived, and there was a problem, with the larger capacitor being a couple of millimetres too high for the case lid to be re-fitted. After some trial and error, I managed to fit the capacitor lying down so the lid would fit. I tested the charger, and it was working again. My wife went to use it and said, it’s not working; the LED is staying green. That was annoying, as I thought it was fixed. I had a close look at the underside of the PCB and found several dry joints on the transformer, which I had not noticed earlier, shown in the photo. I re-soldered the dry joints and gave the charger back to my wife after gluing the lid back on again. She put the battery on charge, and it was charging, but it was bedtime, so she unplugged it for the night. The next morning, when she went to finish charging the battery, the LED was green and flashing slowly. This was becoming annoying, so I removed the lid again. I suspected that the 50V 10µF capacitor before the transformer might be the culprit, even though I measured an ESR of 1.8W, which was within limits. siliconchip.com.au I checked my stock of salvaged capacitors and found one with an ESR of 1.2W, then fitted it. This solved the problem, and the charger was definitely working correctly this time. I glued the lid back on again, and that was the end of the drama. Having a spare charger saved the day, and the repair saved us from spending $39.99 on a new one. Bruce Pierson, Dundathu, Qld. Icom IC-271H Repair About two years ago, I bought a faulty Icom IC-271H 2m transceiver. Dating from around 1985, it was one of the better radios of its day. It operates on 144-148MHz with FM, SSB or CW modulation at up to 100W with 0.3µV sensitivity for a 10dB signal-to-noise ratio (SNR). Although it was advertised as faulty, it didn’t appear to have anything seriously wrong with it, and at $100, it seemed a gamble worth taking. As it turned out, the repair process became quite a saga. The radio came without its 13.8V 20A power supply, but I already had suitable supplies on hand. On initial testing, it worked on both transmit and receive and delivered the specified 100W into a dummy load. However, after a short while, the green RECEIVE LED on the front panel went out, indicating that the phase-locked loop (PLL) had lost lock. When this happened, the receiver was also muted. The full service manual was easy to find online. The circuit of the VFO section (overleaf) is extremely complex; the block diagram (also shown) is a much better way to understand what’s going on. All frequencies are ultimately derived Items Covered This Month • LED gym sign repair • Bruce Pierson’s tales (WiFi repeater & leaf blower) • A faulty Icom transceiver from 1985 • A quick fix for an LG washing machine • The long (air) con 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 Australia's electronics magazine August 2026  83 from a 10.24MHz crystal oscillator. There are two PLLs: a coarse loop covering 102.30-106.30MHz with 100Hz resolution, and a fine loop covering 115120MHz. The fine loop is divided by 500, producing a range of 230240kHz with a 10Hz resolution. The 10.24MHz reference is tripled to 30.72MHz and mixed with the 230-240kHz signal to produce a narrow range of 30.95-30.96MHz. This is passed through a crystal filter and then mixed with the coarse PLL output to give a range of 133.25-137.25MHz. With the 10.75MHz IF, this results in the required tuning range of 144-148MHz. The exact frequencies differ slightly from those shown in the block diagram, as there are country-specific versions. I carefully followed the tuning procedure in the service manual, with no success. The radio would lock for a while, sometimes for up to an hour, then drop out again. I also changed most of the electrolytic capacitors on the board for new ones, but that did not help. As you can see from the photo, the circuit board is tightly 84 Silicon Chip packed and finding suitable components to look at waveforms was very difficult. There are no test points as such; the service manual just gives component locations to look at. After some hours of getting nowhere, I gave up. As it wasn’t urgent, I put it aside and moved on to other projects. There it remained for about two years! Recently, I finally came back to it. Tracing the frequency chain more closely showed that the coarse PLL stayed locked, while the fine PLL was the culprit. Referring to the circuit, the control voltage from pin 1 of IC6 drives varicap diode D9. When locked, this voltage sat between 2V and 4V. As soon as the lock was lost, it jumped straight to 5V and remained there. Australia's electronics magazine siliconchip.com.au The divided-down signals from IC9 and IC8 looked correct, which pointed suspicion at IC7 (M54466L) and/or IC6 (M54929P). A quick search suggested that both seemed unobtainable. I decided to try replacing the entire board with a much simpler design using an Si5351A frequency generator, which is cheap and readily available. The radio’s processor board produces five bytes of binary-coded decimal (BCD) data, the coarse range on DA1 to DD1 and the fine range on DA2 to DD2. These represent 10210 to 10470 and 23000 to 24000, respectively. From these values, the required output frequency for the Si5351A can be calculated. The top two digits in each range never change and can be ignored for the calculation. I designed a small PCB using an Arduino Nano module and an Si5351A module, both of which I had. The control software, written in BASCOM-AVR, was straightforward. I also added an OLED display and an RS-232 interface for development and diagnostics, which were disabled once everything was working. The completed module is shown in the photo and is essentially a two-chip solution. After a debugging session, the Si5351A was producing the correct frequencies and was installed in place of the original board. It did work, but two problems quickly became apparent. First, when spinning the tuning knob rapidly, the system couldn’t keep up. Decoding the BCD data and sending multiple bytes serially via I2C to the Si5351A simply took too long. This was not a deal-breaker, but annoying nevertheless. The second problem was more serious. As I tuned across the band, numerous ‘birdies’ appeared. The spectrum plot appeared to be fairly clean; only the second harmonic was significant. I am not certain where the spurious frequencies came from; possibly noise from the processor chip. This made the solution unworkable. In a sense, I was back where I’d started, but with one important difference. In the meantime, I had located a supplier for both the M54929P and the M54466L. The former was only available as a used part, but the latter was new. The total cost was around $35, including postage, from China. The diagram on the opposite page is the circuit diagram for the VFO section of the ICOM IC271H, while the adjacent diagram is the block diagram for the PLL (phase-locked loop) section. The module shown above is an Si5351 frequency generator. siliconchip.com.au Australia's electronics magazine August 2026  85 A couple of weeks later, they arrived and I installed them. I fitted a socket for the 16-pin DIP device and soldered the 8-pin SIP chip directly, as before. Once again, I went through the alignment procedure, and this time everything locked and stayed locked. I left it running for a whole day and it stayed on frequency. Almost by accident, however, I discovered another problem. The adjacent logic board contains many 74-series devices, mostly LS types, but one was a plain 7404. When I touched it, I almost burned my finger. Measuring the case temperature, it was about 65°C. Standard 74-series parts are power hungry, but this was excessive for a simple hex inverter. Despite this, it appeared to be functioning. A local replacement would have cost about $4, but after rummaging through boxes containing decades worth of accumulated chips, I eventually found a 74F04. It looked unused but the pins were badly oxidised and needed cleaning. I fitted a socket just in case, but the F-series device worked perfectly and ran cool. I have not included some blind alleys I went along and red herrings I came across on the way. Diagnosis and coming up with a solution to a problem is not always a linear process! With the benefit of hindsight, I should have foreseen some of the problems that would occur with my digital replacement scheme. While I can’t claim to be particularly proud of my troubleshooting performance, I did learn a great deal in the process. Despite its complexity, the original PLL design produces a clean, stable signal and very smooth tuning, something that proved very difficult to replicate with digital techniques. Full marks to the original designers. To make certain all was working, I connected it to a dummy load and tested the transmitter. It worked well and the power output was as per specifications. In the end, I have a transceiver that cost me $100 to buy, and probably another $80 worth in parts during the various repair attempts, most of which I already had in stock. It’s now a classic radio in excellent condition, with a second-­ hand value of around $800. Charles Kosina VK3BAR, Mooroolbark, Vic. 86 Silicon Chip LG Direct Drive front-loading washing machine fix In early December, my 19yo daughter decided she would do some washing – a rare occurrence given she mostly lives in her bedroom. I received a panicked call saying “the machine is not working and displaying LE Error”. I got her to try to rebalance the load and try again, but the error came back. In the meantime, I went to serviceman Google and found it was a pretty common fault with the HAL (Hall effect) sensor. I got home and tried to take the part out to check its resistance but hit a stumbling block trying to remove the 17mm bolt that holds the cover to the drive. It really needed an impact wrench, but I don’t have one. I tried dial-a-friend (also known as my brother-in-law) but he was away. After two hours of thinking and trying my socket set to no avail, I realised I had an air compressor with an attachment. I wheeled it over to the laundry and voilà, one bolt removed. The rest of the drive was held in place by six Phillips-­head screws. With these removed, the drive assembly came straight out. I was then able to check the resistance on my HAL sensor by probing pins 5 and 1. It should give a 10kW reading (likewise pin 4 and 1, from memory). On my unit, one reading was open. The exposed washine machine motor and the replacement sensor. Australia's electronics magazine siliconchip.com.au As I was about to go away for a work trip the following day, I decided to order a replacement from Amazon as they offered same-day delivery so I could get it working. The part arrived by 7pm. I checked it with the multimeter and the new part was giving me 10kW on both pins. The reinstall took five minutes, and it worked, which made my wife happy as she was worried we might be up for a new machine. I still think 10 years is young for a washing machine, and this one appears reasonably well-built. While the part was only $17, I wanted to see what had gone wrong. I pulled out all the potting epoxy and finally had the circuit board clean enough to inspect. Aside from a few other components, it includes two pairs of 680W resistors in parallel. One pair was fine, but the other side was open-circuit. An online order and a few days later a strip of 680W SMD resistors arrived. The hot air got the old ones off easily, and there was still ample solder to reuse to put the new ones in. Sure enough, the fault disappeared and both readings were 10kW as expected. After reapplying some new potting epoxy, I now have a spare part should the recent replacement part fail. I’m usually more of a tinkerer than an electronics repairman, but this was one of the easiest repairs I have made. Roberto Marin, Earlwood, NSW. Conned by the air-con I buy split-system air conditioners and install them myself. It is not hard, just requiring simple gauges and a vacuum pump. There are some lessons to be learnt about flaring copper tubes, especially regarding flare length and lubrication. Anyway, I installed such a unit from a ‘big green shed’ for a guest during winter (it gets cold here!). It worked perfectly, heating the guest room. Come summer, we had more guests who asked me to check the air conditioner. It turns out that the unit would heat but not cool! I knew it had gas and was acting as a heat pump; otherwise, it wouldn’t heat. I removed the cover from the outside unit because it’s the easier one to work on (like how a drunk person searches for their keys at night under the streetlight because it’s easier to see there). There is very little in these units: the compressor, a four-way valve, a fan and a heat exchanger. When set to heat, the four-way valve was powered up and the fan operated – good. When set to cool, the four-way valve was powered up, but the fan was off! The four-way valve is supposed to be off in this case so it doesn’t reverse the working fluid path to provide cooling. The fan certainly needs to run to dissipate the heat being pumped out. After much head-scratching (you may add lots of words here about troubleshooting), I realised that if the functions were swapped, the unit should work correctly. Long story short, swapping the control wiring solved the problem. I thought that I must have made a mistake in the control wiring, but I checked the instructions and I had done everything correctly. I then suspected the manufacturer had made an error with the control wiring, but again, no; checking it all, it looked correct. So the problem must somehow lie in the control system board itself. It was at this point that I was told, “It ain’t broken, so don’t fix it”! Apparently, I have an issue with having to fix things! Even our guest, who was a senior lecturer in electrical engineering, wouldn’t support me in further troubleshooting! SC Garry Woods, Watson, ACT. siliconchip.com.au Australia's electronics magazine August 2026  87