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SERVICEMAN’S LOG A damp sort of holiday Dave Thompson I recently had to go on holiday again. I know what you’re thinking: that sounds a bit iffy. Still, please hear me out. About eight months ago, we went to Airlie Beach in Queensland, Australia (which is in the same country this fine magazine is produced). We went mainly for the Whitsundays and the Great Barrier Reef, and also to try to escape the drudgery of our day-to-day working lives by seeing and experiencing something really new, all without having to travel for 45 hours to further climes. It was certainly beautiful there, and the reef was stunning. It was everything we imagined, and more, though we of course were just like any other tourists – the locals likely hated us for being there, choking up their cafes and restaurants, while blocking their footpaths and venues as we saw the sights. We were so enamoured that we decided to book another break, this time to the northern end of the reef, basing our stay in Cairns – which lays claim to be the gateway to the Great Barrier Reef (although we never did find that famous arched sign they use in all the Cairns tourism promos). It helped that we had friends living there. Even our friends and local merchants didn’t know where that sign was; still, local knowledge is everything, and we took a lot of advice from them. Anyway, this isn’t a travel column. But stay with me, because it gets interesting – from an engineering point of view! So, I had to go on this holiday. It was booked well in advance, and well-planned by her in-laws, so my role was simply to tag along and carry the heavier bags. We sorted our house here, as in getting someone to look after it and feed the cats, and departed for the airport at some ungodly hour in the freezing cold (why do all flights anywhere from here leave so early? I must find out...). At this point, being in the tropics seemed very appealing! It’s weird to walk into an airport in winter clothes and arrive six hours later sweating like an English prince in the glare of the world’s media. We knew some people from here who had been to Cairns the week before; they had said it was perfect weather, and we’d be right. Brave words! going well. So, we thought we’d made a sensible decision. We stayed in an apartment booked through the usual systems that are in vogue now, and we were surprised to find when we arrived that there were about a gazillion apartments in this relatively new harbour-front complex. I guessed tourism is increasing there, with the number of rooms they have in the town. Many of these apartments were managed by, um, the management of the complex, but many were also individually owned and some rented out by the owners, the latter describing the one we were staying in. When we arrived and were shown around it by a lovely woman, we were impressed. It was well-built and well-­ appointed. It was clean and obviously had been well looked after. My serviceman’s ears and eyes picked up some things that didn’t quite fit the brief, but all in all, it was a place to get our heads down at the end of a gruelling day braving the weather and being the tourists we were. Arriving in Queensland A little taste of home When we arrived, it was raining. And I don’t mean rain like we get here (drizzle, really), but rain you would need gills to survive in. This introduced us to a new phrase that we would hear a lot during our ten-day stay. “You’re in the tropics now”. OK, we know that Cairns is getting up there latitude-wise, but this wasn’t supposed to be monsoon season. We didn’t go there without doing some due diligence and understood that the ‘monsoon trough’ that they all talked about there would likely hit properly a few months after we’d left, all My first interesting observation was when we arrived on the third floor and exited the lift. It was freezing in that hallway. I don’t mean a little cold; I mean like being in the chiller room of a booze shop cold. We could see our breath. OK, aircon is essential in some places, especially when it is 30°C+ outside, but this seemed excessive. The downstairs areas were nowhere near as chilled as this. When we got to our apartment/room and she opened the door, I heard a weird whistling sound as we entered and the door closed behind us. I put it down to a noisy door-closing 88 Silicon Chip Australia's electronics magazine siliconchip.com.au actuator; you know, those pneumatic or hydraulic devices that are mounted at the top of doors and close them automatically, once opened. But something was a bit off; the sound wasn’t quite right. But we’d only just arrived, so I assumed it was just a quirk of the room. Once we were settled in and unpacked, we took in the lay of the land. This place had several ‘French’ doors that opened onto separate balconies. The first thing I noticed was that there was a considerable gap in the bottom of the ‘main’ balcony door, compared to the tight fit at the top. It also didn’t open very easily, not running in its track that well. This meant the building was off-square, something I notice in Christchurch a lot now after the quakes knocked many homes out of plumb. This in itself isn’t a problem; many homes are not as square as they were when they were first built. But this factors into subsequent events. The first indication there was a problem was the low whine that came into the bedroom when we went to bed. No, this was not me complaining about the bed. It appeared to be coming from the windows that faced out to the balcony, except there wasn’t a breath of wind outside. Rain, there was lots, but wind? None. I went and opened the main door to see if I could find the source, and the noise suddenly stopped. Closing the door again started the sound, even before I could completely close it. I discovered I could open it about a centimetre at handle height and the noise disappeared. As sleeping with this sound was not an option, we had to leave the door open slightly. No problem; it was hot and humid, but we had ceiling fans and aircon happening. Indoor pool There was another problem when I got up the next morning and stepped into a pool of water in the kitchen. This is, of course, concerning. Everything in that area (by the balcony door) was soaked in water. I turned on the main light and got down to look along the floor to see what was going on; my thoughts were the fridge/freezer had defrosted or there was a leak from the apartment above. There was a puddle under the fridge. When I looked closer, the whole fridge was wet, so that if I ran my finger down it, water dripped off my hand. But the water was all over the floor, not just by the fridge, all the way to the entry door (the one that whistled). This warranted further investigation. It wasn’t the best way to start a holiday! I cleaned up with towels as best I could and contacted reception, who told me that, as they didn’t manage this apartment, I had to talk to the landlord. This I did, and he was great and said this hadn’t happened before and he’d get right onto it. In the meantime, I investigated further. The bulk of the water was coming from the entry door, which opened out into the frigid hallway. The inside of the door was dripping profusely, and all around the frame and the door closer. The walls nearby were damp, but not awash like the door was. The card lock and closer were also rusted around the edges – not much, but enough to imagine that ‘this not happening before’ might be a bit of a fudge. I also noticed that opening any of the windows or the balcony doors not only solved the low hum but also resulted in the entry door not whistling when we opened and closed it. Interesting indeed! siliconchip.com.au Items Covered This Month • A damp holiday • Repairing a YaeCCC DC power supply • Fixing a Victa slasher lawnmover • Going back to an old design 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 Someone from the building maintenance team came up and checked the flat upstairs, but said there was no one in it and no obvious leaks. He then came down and looked into our place and said it looked a lot like condensation. If this were the case, why had it never shown up before? I’d certainly never seen such a thing, and I am no stranger to being in ‘the tropics’. Of course, the obvious answer as implied that it was somehow our fault, not running the ceiling fan (which we did) or not running the aircon (which we also did). Not a big fan The interesting thing about this place was that it had two bathrooms, and each had an extractor fan that we couldn’t switch off. These were no wimpy extractors like you can buy at the local big box store – from their noise and power, I think there was a Rolls Royce jet engine somewhere on the roof running these in most apartments! Now, I understand that keeping the air moving in apartments in ‘the tropics’ was important, as the humidity outside can be horrendous to people like me who come from essentially cold, dry places. But it seemed weird to have aircon running (also built into the building with control panels in each room) and ceiling fans as well, given that the air was being extracted, anyway. So, with our apparent inexperience of these systems in the tropics, what do we run? The extractors are obviously there to keep humidity down, but we Australia's electronics magazine January 2026  89 didn’t realise that then; we just assumed they were there to keep the bathrooms from steaming up (especially since one had the clothes washer/dryer in it). The landlord and the management of the complex, who had been involved, recommended we keep the doors and windows closed and both fans and aircon running at all times, as the outside humidity had been extremely high the past few days due to the non-monsoon-type rains. The resort receptionist, who was very helpful, told us that many mornings when she came in, she had to wipe down the walls behind her and the big reception desk in front of her. The ‘lobby’, such as it was, is open to the elements (though under cover), but there are no closing doors or even glass walls to the street outside. Residents and guests can just wander in from the car/bus drop-off area up to the desk. This must have played havoc with the three computers and many phones they had lined up along the desk, but I guess that’s just part of the job! A few quirks to the room and complex, then. The problem remained though; the entry door sweated badly, and the fridge doors also poured water onto the floor. And the hallway outside was freezing. My serviceman’s brain told me they must be related. Back to normal A day later – after lots of extra towels were dispensed to help us clean up the now constant water, we went out and to our surprise, the hallway was at a normal, cool-but-notAntarctic temperature. We mentioned this to the reception people, and they said yes, the aircon on that floor turned out to have been faulty but was now fixed. At least we wouldn’t freeze coming back from the pools... We spent the day out, returned in the evening, and our room had dried almost completely, with only a few drops beneath the door. The fridge door was dry, as were the previously damp walls and entry door fittings. Interestingly, the whistle didn’t happen either when we opened and closed the door, a sound we had almost gotten used to. Nor did we hear anything when the balcony doors were shut – no low annoying hum to keep us awake and requiring that we crack the windows or doors. It likely also helped that now the weather was not so monsoonish (although locals were seemingly always at pains to tell us that the previous day’s rains were nothing like the actual monsoon season!). I think what was happening was a kind of a perfect storm of circumstances (I know, just our luck!). Firstly, it was teeming down outside, so both the temperature and humidity were very high, as was the atmospheric pressure. Next, the very cold temperature in the hallway of the apartment building. The various floors are essentially sealed and climate-controlled areas, with fire doors and interconnecting security doors. Only the ground floor/ outdoor/pool areas were open to the weather. This created a low-pressure system inside the building, which was worse on our floor, where the aircon had gone into Antarctic mode. This also generated the whistling and humming when our windows were closed, or the main door opened, despite the fact, or perhaps because of, the gaps in the room’s joinery. So the front door was freezing on one side, warmer on 90 Silicon Chip the other, and the pressure in the room created an environment for condensation to build like crazy, resulting in us having to mop the floor. I would have thought the extractor fans and aircon would have seen to it, but they simply couldn’t cope with the amount of humidity, and the pressure/temperature difference between the rooms. Sadly, by the time we had all that sorted, we were due to leave. It was a very nice place, but I’m sure all the rooms on that floor would have experienced the same perfect storm of broken aircon, high atmospheric pressure and unseasonal humidity. As an aside, I did find out how to disable the annoying extractor fans, which were quite loud. Even though they put out a white/pink noise vibe, they were still distracting when trying to get to sleep or even watch TV, on top of the noise of the air conditioning system. The day we were packing up to depart, we went down to the pool for one last dip. When we came back up after lunch and drinks, the hallway was frigid once again. We called reception and advised them, but as we were leaving, we just wanted to get our stuff and go. The whistle at the door was back, and the hum from the doors and windows, and of course, the condensation had started to build up on the door and frame already. This was despite the fact that it hadn’t rained for the past few days, and the humidity wasn’t nearly as high as it had been. The pressure difference was still obvious, though; as they say up there, it is just a fact of life in the tropics! YaeCCC DC power supply repair I bought this power supply online when I started working from home pre-COVID-19, so it’s probably six years old. It wasn’t expensive; in fact, it was probably the cheapest one I could find. I don’t know how to say the brand name; however, I’m sure one of my old colleagues would have pronounced it “Yuck”! Still, it has been good, and I can’t complain. I use it most working days, sometimes all day, although usually at way less than its 6A rating. The Yuck is a switch-mode design with no linear regulator, so it probably is a bit noisy. However, my work is Australia's electronics magazine siliconchip.com.au An excerpt from the onsemi data sheet showing a DC-DC converter using the TL494. The Yuck PSU is similar but has an extra transformer between the TL494 and chopper transistor bases. mainly with microprocessors, which aren’t fussy in this regard. It has an annoying design characteristic that the output capacitor is after the current limit circuit, so if you set the voltage a bit high, then connect it to a low-voltage load like a light-emitting diode (LED), it will dump the output capacitor into the load, potentially blowing it up. Been there, done that. Any PSU that has the current limit incorporated into the switch-mode control loop will behave like this, and I’ve just learned to live with it. Recently, I noticed noise in one of my designs, and quickly traced it to the output of the Yuck. The noise was pretty significant – a couple of volt spikes at around 60kHz superimposed on the output voltage. It looked like switching noise, so I removed the lid and had a look at the output capacitors. I was expecting one of them to be bulging or to have leaked, but they both looked OK. They measured OK with the Fluke 189 meter too. Just in case the caps had a highESR fault, I briefly tried adding a capacitor to the output, with no improvement. At this point, I was a bit stumped. Switch-mode converters generally feed energy into the output capacitor via a diode – there isn’t really any opportunity for anything to get out of whack and noise to suddenly appear. When there’s voltage at the transformer output, the diode conducts it into a capacitor, and when there’s not, it doesn’t. Some switch-mode supplies replace the diodes with a Mosfet synchronous switch – if one of these was driven at the wrong time, it could conceivably result in spikes, but this PSU is an older design and just used two diodes. The main controller was a TL494. Looking at the Texas Instruments data sheet for it, I didn’t see anything about output noise, apart from layout guidelines – the layout wouldn’t have changed recently. For good measure, I also looked at the onsemi version of the TL494 datasheet, and it didn’t give me any clues either. The TL494 is a bi-phase PWM controller – it drives two switches out of phase. Both switching transistors looked OK and showed the same values on the meter. Same for the output diodes. siliconchip.com.au The data sheet shows a possible DC/DC converter design – the Yuck was generally similar to this, but includes an isolating drive transformer between the TL494 and the switches, since the switches are chopping rectified mains. Looking at the signals with the oscilloscope, you’d expect to see similar waveforms on both phases. Since I didn’t have a mains probe, I looked at the transformer outputs (ie, the output diode anode) and found the opposite – one side looked pretty regular, but the other was far from it. I found similar results at the TL494 outputs, before the drive transformer. I wasn’t sure what this really meant, but it didn’t look right, so in the absence of any better idea, I thought about replacing the TL494. My local Jaycar didn’t have them; however, the Bankstown store had packs of 10 on clearance for $2.95 plus postage. So I ordered a pack of 10 – two packs of 10 arrived a couple of days later. I’m not sure why I received two packs – I can only think that Jaycar must have really wanted to clear them out! Australia's electronics magazine January 2026  91 Fitting a new one was fairly quick, and I managed to do it without lifting any pads. Powering on, it worked first time, with no problems at all. No noise, just like was when I bought it. I still have no idea how the controller could drive the switches in a way that makes the output noisy. However, I’m just glad my PSU is back working; I need it. If anyone needs an SMD TL494, please let me know; I have a few spare! D. T., Sylvania Southgate, NSW. Victa Slasher repair Around 30 years ago, I bought a Victa 160cc 24-inch (61cm) slasher from a friend. We have five acres here in Queensland, and I use this slasher to mow around the boundaries and a 5m-wide table drain at the side of our property that brings runoff from the street into our dams. Over the years, I’ve done a lot of mowing with this slasher, and I have reconditioned or replaced the 160cc twostroke engine several times. Being a retired small engine mechanic, this is no problem for me. I even managed to pick up a couple more of these 160cc engines at the local tip shop around 20 years ago. My most recent repair was a couple of years ago, when I put new piston rings in the engine. Spare parts for this now over 50-year-old engine are getting really hard to find, so there will come a time when I will have to replace the engine with a different type. When the time comes, I may replace it with a Honda four-stroke engine, but I want to keep the Victa two-stroke engine going as long as I can. Having a bunch of spare parts in these spare engines has proved to be very helpful in achieving this. Sometimes I use parts from one of the engines, or I may rebuild one of them to replace the existing engine. Over the last couple of years, the slasher has become increasingly difficult to start. I knew what the problem was; it was the condenser, which is a 180nF 260V AC rated capacitor. I had been looking for a replacement for some time, but I could not find one to suit the early Series 70 engine, as it is smaller than in later engines. This difficulty starting got to the point where I had to pull the zip starter rope around 30 times to even have a chance to start the engine. I resorted to taking the zip starter assembly off the engine and using my electric drill to start it. I dismantled a couple of the spare engines to locate a replacement condenser. I found one that I could use, but then I decided to replace the entire magneto assembly of the coil, points and condenser. I got the parts I needed, so I removed the zip starter and flywheel from the engine on the slasher and removed the existing magneto assembly. After installing the new (used) assembly, I got out my buzz box (a type of continuity meter) to set the ignition timing. At first, the buzz box was making unusual sounds; I suspected that the 9V battery was partly flat. The Victa Slasher lawnmower (left), and the buzz box (above) that was used to set the ignition timing. 92 Silicon Chip Australia's electronics magazine siliconchip.com.au I opened the case and removed the battery and tasted it with my calibrated tongue. It tasted like it was about 8V, which would explain the unusual behaviour of the buzz box. With some experience, it’s possible to estimate the voltage of a 9V battery pretty closely this way. I got my multimeter out and tested the battery and, sure enough, it read 8.1V. I got a new 9V battery and fitted it to the buzz box, then used the buzz box to set the ignition timing at 0.25 inches (0.635mm) before top dead centre. After reassembling the engine, it started on the third pull – a good sign! The following two times I used the slasher, it started on the first pull. Another successful repair to keep this old slasher going for some time to come. Bruce Pierson, Dundathu, Qld. PICAXE doorbell repair I submitted a circuit that appeared in the May 2004 issue’s Circuit Notebook section (siliconchip.au/Article/3525). It was my first attempt at producing a useful circuit utilising the then-new PICAXE 08M microcontroller. It simply monitored our outside staircase using a beam-break arrangement made from IR transmitters and receivers at the bottom and top of the stairs. When triggered during the day, it rang a doorbell; at night, the bell rang and it switched on outside lights via a solid-state relay (SSR). Coming down the stairs, there was a delay of 20 seconds for the bell, but the light would switch on straight away at night. Today, all this could be done with ready-made devices. After all this time, it works perfectly apart from one of the four bells/chimes having stopped working, and another having started sounding sick. We require four, as our house is large and we wish to hear someone approaching the front door, especially if we are in the backyard. I took the back cover off the mains-powered chime and, as expected, found a mains capacitive voltage dropper circuit regulated by a 5.1V zener diode. The components looked pristine, so after removing the 1.5μF 450V X2 capacitor, I was shocked to find it only read about 390nF. That value still allowed the zener voltage to be correct off-load, but it dropped significantly when commanded to operate the chime. The functioning doorbell with a 1.5μF capacitor at 50Hz will have a capacitive reactance of around 2.1kW, giving about 113mA of available current. Falling to 0.4μF, the reactance increases to about 8kW, only providing about 30mA. The second bell/chime had the same problem, but its capacitance was just below 1μF. Replacing both 1.5μF capacitors solved the problems. I have since read that this is not an unusual problem with metallised polypropylene capacitors. With transient voltage surges over time , the X2 capacitors ‘repair’ themselves, producing holes in the foil layers due to the self-healing process. This prevents short circuits, but the capacity diminishes each time. Eventually, the value is so far below the rated capacitance that the power supply no longer works. A multitude of devices are powered by simple capacitive dropper circuits like this. They include bathroom, bedroom and passageway low-wattage security lamps and standby power supplies for many home appliances. The list is large, and I wonder how many things have been thrown away because of an X2 capacitor that has lost its capacity. SC Paul Walsh, Montmorency, Vic. siliconchip.com.au Australia's electronics magazine January 2026  93