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SERVICEMAN’S LOG Ion with the wind Dave Thompson Servicing can be a strange industry. These days, much of what comes through the door is not designed to be repaired. You can imagine how that makes the job a bit of a challenge! I understand that companies want to protect their designs. Still, if someone wants to clone a product, unless it uses cutting-edge technology, they can do it without too much difficulty. Making devices unrepairable usually has the most significant impact on the customer – someone that the company making the goods probably should want to keep happy! Someone, somewhere, always has the wherewithal, resources and ability to ‘deconstruct’ or ‘reverse engineer’ something to find out how it works. If the mood or the promise of commercial gain takes them, they will replicate it and sell it, likely at a lower price. Many countries’ economies are seemingly reliant on copying the ‘intellectual property’ of others. Some of these ‘clone jobs’ are so shameless that they replicate the external appearance of the original product, down to the shape, the colours and even the font. They just replace the original company’s name with their own and sell it for a fraction of the price! I think this is a basic human instinct, illustrated by the fact that I (like many others who would be reading this column) pulled many things apart when I was a wee fella to see what made them tick. Dad had to put most of them back together – that is, until I could do it myself. My first guitar builds were attempts at making copies of existing models as I tried to make an instrument I could afford, hopefully as good (if not better) than those available for what were, to me at the time, vast amounts of money. Whatever the motivation behind copying others’ work, it still happens a lot today. That said, finding an epoxy resin-potted ‘module’ in a commercial unit may have another more practical explanation than obfuscation. Ionisers are positively great Recently, a client brought in a device I’ve not seen for many years; a commercially-produced air purifier/ioniser. These devices were all the rage as far back as the 60s and 70s, in a jet-age, sci-fi sort of way, and were the ‘go-to’ gadget for a while. They were also popular as a project in magazines back then. It got me, too; the subject of purifying air using electronics fascinated me. The result was that I built many negative ion generators over the years, with varying success. However, that didn’t mean all was well in the state of negative ion generators. There have been hundreds of studies showing that negative ions have no real benefit to people or pets, while a similar number of studies have proven that they are beneficial. 92 Silicon Chip Some took them so seriously that hospitals utilised them as part of their air-conditioning systems to minimise or neutralise airborne infections. The recent pandemics (SARS, COVID etc) have resulted in a considerable boost in air ioniser sales. As is typical these days, ‘mileage’ varies with any ‘health’ product. If using one makes one feel better, why not use it? Regardless of the health and well-being implications, making and setting them up is fun and educational. That (for me) makes up for any of the controversies. Many commercial variants are still sold today for use in the health and horticulture industries. The premise of these devices is simple: apply a high voltage to an array of sharp metal “emitters”, and a corona or ion wind will stream from those points. Many airborne pollutants are electrostatically charged by this wind and are attracted to a nearby ground. So the theory of air purification by negative ions is sound. I have seen this for myself; I built several ionisers in the early 1980s for a friend who had a small greenhouse/ hydroponic setup for producing cabbages and cauliflowers. This guy wanted to improve the air quality in his setup, and when he heard me going on (as was my wont) about this new-fangled method I’d been reading about, he was keen to bankroll a couple to see how it worked for him. I scaled up a project from an American magazine and set them up in his greenhouse. They sat on a large baking-tray type metal plate that was Earthed through the mains, and sandwiched between that and the ioniser was a sheet of white paper. After just two days, that paper was turning grey, and when the ioniser was moved, there was a stark white outline where it had been sitting. That proof was good enough for me. Those ionisers ran for the next 15 years until the guy moved, and I was sold on the idea. The last one I built was for a person here who suffers from a seasonal complaint we call “Nor’ West Syndrome”. We get a very hot, dry, gusty wind during the spring and summer months, prevailing from the northwest. It is loaded with pollens and dust picked up by roaring over the nearby Canterbury Plains. As it blasts through Christchurch, it dumps that pollen in buildings, on the ground and anywhere the air reaches. It looks like yellow, granular dust and is sometimes everywhere. Those with hay fever or any sensitivity to pollen or dust can have serious health impacts due to this phenomenon. When this person complained to me about it, I suggested an ioniser might be the answer, especially if set up near Australia's electronics magazine siliconchip.com.au Items Covered This Month • • • Ion with the wind A nomadic TV antenna Repairing a microswitch in a washing machine 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 their bed. I initially built one ion generator for them, then another for their home office; they swear by their use now. Unrepairable but not unbreakable The one that came into the workshop recently is a commercial unit, made in China, and is quite small compared to others I’ve encountered. It runs from a 9V battery and is designed to sit on a bedside table or similar. After determining the battery was good, the only real option was to pull it apart and have a look. There were no screws; it was clipped together, so I got the client’s permission to (literally) crack it open. Inside was a solid mass of black potting compound. There was absolutely nothing I could do with it repairwise. Many such devices are potted like this inside, not to mask the circuitry (although that might be a useful byproduct) but more likely to prevent corona bleeding or arcing between all the components that are in very close proximity. Most of these devices work the same way, though there are different lines of thought regarding the power input. Some apply a relatively low DC voltage (usually from a plugpack supply), via a simple switching circuit, to the primary of a transformer. The stepped-up transformer output then goes through a voltage multiplier circuit. The resulting HV output terminates at the pin array, though sometimes it can just be a single-pointed electrode/antenna. The other method is to use mains power directly into the multiplier circuit, sans transformer (although some use a 1:1 transformer for isolation). But I doubt that is legal here; the whole circuit would run at mains potential; perhaps another good reason to pot everything solid! The output voltage (around -3kV to -10kV depending on the circuit) is safe for anyone touching it (the output pins may be accessible through holes in the case), yet it’s high enough to cause an ion wind to stream from the points. This wind can usually be felt by placing a (wet) finger close to the emitter array, but note that some ionisers employ a fan to fudge/boost the ion output. You might think getting too close to the pins could be dangerous; sometimes, a tiny, weak arc to a fingertip may be visible in very low light. But a line of high-value resistors in series with the HV feed to the pin array limits the available current to a safe level. The idea is that the negative ions from the emitter pins charge any muck in the air, and this finds its way to the nearest ground. Most commercial units don’t come with a ground plane to sit on, or a handy connection to add one, siliconchip.com.au so we can only assume the particles find something else grounded enough to be attracted to. Also, some of these commercial devices are tiny, about the size of a small mobile phone, so it is hard to see how they can be as effective as those boasting a decent-sized pin array. Either way, this device wasn’t running, and there was nothing I could do. They are pretty cheap to purchase off the internet, so I wasn’t sure this would be a feasible job anyway. I talked to the client about it (good communication is essential to a serviceman). In the end, they commissioned me to make one of the models I’d produced before (and likely harped on a bit too much about!). Do it yourself! While not overly complex in the models I build, the actual electronics involved are pretty interesting from a theoretical point of view and are good fodder for the home experimenter. Anyone who likes watching big arcs and making circuits with the potential (!) for lots of high-voltage experimentation can use a very similar layout to power up the likes of Tesla coils and Jacob’s Ladders. The main difference with this circuit is that we want to keep arcs out of the equation as much as we can and feed all that juicy HV energy to the pin array. If we get a flashover at any of the connections on the multiplier, not only do we create a fire and shock hazard, we lose any semblance of decent ion emission at the output. The circuit I use consists of three sections: a driver/ oscillator section, a multiplier/output section and the pin array. Each section has its own circuit board. Anyone familiar with such things would recognise a Cockroft-Walton arrangement of high-voltage capacitors and diodes in a characteristic criss-cross ladder outlay. This is actually a line of half-wave rectifiers connected in series, with each stage boosting the previous stage’s output ever higher. Theoretically, you can just keep adding stages. As long as your components can handle the resulting voltage (and the spacing between components and stages is enough to prevent arcing between them), Australia's electronics magazine June 2022  93 you can get some seriously high voltages out of such a setup. Practically though, it’s a different story. One significant consideration is what to assemble these components on. I could use veroboard or perf-board, but I’d spend most of my time stripping tracks and arc-­proofing it. A better option is to use a printed circuit board with the correct spacing already worked out. Fortunately, because I throw nothing away, I have a spare set of boards from the run of ionisers I made back in the day. These are very much home-made, meat and potatoes PCBs, not like the multi-layer works of art we see today, but they still look good and do the job, which is all I want from them. The driver board boasts a board-mounted barrel jack for DC input (typically from a 9-15V plugpack) powering a 555 timer configured to run as an astable multivibrator that, in turn, drives two NPN power transistors in a pushpull configuration. The relatively square-wave output from the transistors switches current through the primary of a custom-wound transformer. A few other ancillary components ensure everything runs as it should. The secondary of the transformer runs off to the multiplier board. If this sounds familiar to some readers, that is because the April 1981 issue of Electronics Today International (ETI) (which we offer scans for siliconchip.com.au/ Shop/17) featured a very similar circuit. This circuit is also quite close to most oscillator-based ioniser circuits from around that time and even some I see on the web today. I changed it slightly to upgrade the transistors, included heatsinking and added two extra stages to the multiplier, altering the PCB artwork to suit. The rest of the build involved making the transformer and the pin array, both tasks which can put constructors off. But while they both seem to be quite tricky to make, neither is overly difficult. The transformer uses a standard ferrite pot core and bobbin, and it is just a matter of winding the coils carefully and 94 Silicon Chip neatly, insulating well between each layer. I made a jig years ago for such things and keep it handy, just in case. While the wire is still wound by hand, holding the assembly is much easier, and the resulting windings are much neater. This component is the most critical, especially when adding extra stages to the multiplier because the transformer will break down internally – usually before anything else – should the HV output go too high. The pin array is a little trickier, but I used a 0.5mm PCB drill bit and a small manual hand drill to carefully bore the holes for modified (head cut off) dress pins through a 120mm length of 4mm brass tube. Getting them all in line is probably the worst part of it. Still, given that they can be easily bent into shape if they are off-angle a little, it isn’t too onerous. Soldering the pins in is also a bit of a challenge, but I use liquid flux and lots of solder, and it seems to stick them in OK. I also fill the ends of the tube with solder and sand that and each pin end smooth to ensure there are no sharp edges – ions will ‘leak’ from anything sharp. This is also why the capacitors and diodes in the multiplier must be soldered to the PCB with their leads cut very close and what I would usually consider too much solder; a nice round blob will be less likely to arc to another nearby joint or bleed ions. We want all the ions coming from the sharpest parts – the pins. Once it is up and running and mounted in a nice case, the question is how to know it is working. Other than sticking your hand in front of it and hoping to feel the corona wind (no, not that kind of corona!), the ion output can be measured using a simple detector. That ETI version I mentioned included a tester that supposedly lit up when ions were present, but I could never get it to work. That could be because the PCB I made for it wasn’t good enough, the components were not quite right, or perhaps the ioniser I built at the time didn’t work well enough to trigger it. Regardless, I ended up making a little hand-held meter with a couple of transistors and a whip antenna that picked up negative ion emissions quite well. I use that now – not that I build many of these things – but when I do, it’s nice to have the test gear to show they are working. Australia's electronics magazine siliconchip.com.au The client was happy and claimed my version worked way better than their original ever did. That’s always gratifying to hear, especially with something as ‘controversial’ regarding health benefits as air ionisers. The nomadic TV antenna reception G. C., of The Gap, Qld had a lot of trouble with TV reception in his caravan on a trip to Far North Queensland. He traced it to a rather apparent electronic fault... On the first night at Tewantin, we could not receive a single television channel. This was somewhat unexpected as our caravan had been in storage for several months. Before that, we had received television stations without difficulty from the Mt Tinbeerwah transmitters near Tewantin. These UHF transmitters broadcast with vertical polarisation. Most modern caravans use fractal antennas that can receive both horizontally and vertically polarised signals, but our 16-year-old caravan does not have such luxuries. It has a simple Winegard antenna (sometimes called a batwing) with folded dipoles for VHF and UHF signals. It can be raised off the caravan’s roof and rotated in the direction of transmission by a mechanism on the ceiling. Inside the antenna radome is a masthead amplifier that is power-fed through the coaxial cable. The two struts that hold and control the position of the antenna head are in a parallelogram configuration. This enables a simple modification to be carried out that involves raising one of the struts, causing the antenna head to rotate to the vertical position, which is needed at Tewantin. Bypassing the PVR (personal video recorder) and connecting the antenna fly-lead directly to the TV did not fix the problem. Neither did changing the fly-lead or connecting it to the second antenna socket in the van. I checked that there was 12V at the “F” connector at the antenna, and it was fine. As a last resort, I removed the 694MHz filter (to block mobile phone signals) on the drop-side of the power-feed module and, surprisingly, I could then tune in all the channels. It seemed unlikely that a passive device had failed, and I wondered at the time whether its insertion loss was the straw that broke the camel’s back. All went well until we arrived at Rolleston, where the caravan park had a community antenna with coax distribution. Usually, we connect the audio output of the television set to the auxiliary input of the caravan’s CD/radio stereo system. However, with the external coax feed connected to the van, mains hum from an apparent ground loop made listening to the TV virtually impossible. When we reverted to using the television speakers, there was absolutely no sound. We had that problem on a previous trip, and we fixed it by doing a master reset on the TV. But that did not do anything this time, and it wasn’t until a couple of days later in Charters Towers that I had time to dismantle the TV. I was surprised to find that the voice-coils of both speakers were open-circuit. I couldn’t replace them at the time, and when I later got home, I discovered that Sharp no longer sells replacement parts for this set. Eventually, we arrived at Georgetown for a few days exploring. Once again, we could not pick up the single-­ channel broadcast from the transmitter just over 1km away. This ABC transmitter was in the VHF band and transmitted at 4W. Even manually tuning the PVR and TV, I could not find the ABC signal. siliconchip.com.au I decided it was time to check the amplifier in the antenna. It was not easy to get to, as we did not bring a ladder. But by lowering the antenna quite a bit, it was possible to access the F-connector and pins securing the antenna to the struts by sticking my head out of a hatch. These antennas do not appear to be designed to be repaired; umpteen diabolical plastic clips held the two sides of the radome together, plus several plastic dowels from one side to the other, which were ultrasonically welded. When I finally got to the printed circuit board, it was obvious why it was so temperamental – it was severely corroded, presumably due to moisture ingress. I would generally clean a board in this state with isopropyl alcohol, but the best I had on board was plain old methylated spirits. After cleaning it up, there were open-­ circuit tracks that needed replacement. After re-assembling the antenna and re-installing it, it was happy days again when we could receive the ABC. But our joy was short-lived, as after about 90 minutes, there was a complete signal blackout again. The next day, I risked life and limb to again remove the antenna to access the PCB. I checked every plated-through hole with a multimeter and replaced another corroded link. Again, there was apparent success, and the missus could watch her BBC programs. All was well. At Atherton, we could pick up the VHF broadcasts from the powerful Mt Bellenden Ker transmitters but not the UHF The masthead amplifier PCB and components were badly corroded. Australia's electronics magazine June 2022  95 signals from the nearby transmitters at Hallorans Hill. On passing through Mareeba, I was pleased to be able to buy PCB lacquer at an electronics parts reseller and, when I applied it, the board looked much better. But in hindsight, it may have been better to have waited a bit. At Redlynch, Cairns, there is a local broadcast site with all channels in the UHF band, but we couldn’t pick them up. When we arrived at Wongaling Beach just south of Mission Beach, my suspicions that the antenna amp had failed again were confirmed when we could not pick up any UHF channels from the broadcast site on Dunk Island. It was just 8km away, and we could see it clearly. When I again removed the antenna and accessed the PCB, I had a close look at the circuit. The signal split into two paths from the balun: a VHF amplifier with one transistor and a UHF amplifier with two transistors. I quickly sketched out the circuit of the UHF section. At this stage, I got on to the internet to see if there was any information about fixing these boards. There was information about replacing corroded PCB tracks and plated-­ through holes, but someone had figured out that the UHF transistors were BFR93A types. I connected a 9V battery to the output coax connections on the board so that I could make DC voltage measurements. It soon became evident that the second UHF transistor was not conducting at all, even though the base bias voltage was correct. I removed this transistor, which wasn’t easy in a caravan without a fine-tipped soldering iron etc. The missus was the theatre nurse and held a magnifying glass and LED torch so I could see what I was doing, which definitely helped. No wonder we were having so many issues with the antenna – the collector of this transistor was missing! It had totally corroded away. Where do you buy a low-noise RF transistor at Mission Beach? All I could do was bridge the base track to the collector track and see how well the UHF amplifier would work with just one transistor. In practice, it worked surprisingly well, and for most localities, either the PVR or TV signal meter displayed a strength of around 70% and signal quality of 100%. There was only one place when the antenna was pointing at dense vegetation that the level of pixellation was so severe that watching the television was untenable. By the time we got home, an online retailer had delivered a few of the transistors as well as some SMD ceramic capacitors. After soldering in a new transistor, I replaced a filter capacitor that had a corroded end. I also strung an MKT capacitor across the power supply electrolytic. When re-assembling the radome, I siliconed both halves together except for segments to allow egress of any water entering when the antenna is in either the horizontal or vertical plane. The antenna is now working as well as it can, but the real question is: for how long? service manual and parts manual from the Fisher & Paykel website and printed them. Fisher & Paykel must be only one of the few companies left that gives out service manuals. The service manual shows how to enter diagnostic mode, which gives codes for the last eight cycle errors. It also has procedures on how to test the out-of-balance microswitch, the pump and the water valves. The error codes are displayed on the eight wash progress LEDs, with the right-most “spin” LED being the least significant bit and the left-most “long wash” LED being the most significant bit. The code that it came up with was 00101011 binary or 53 octal. The binary decoding table indicates that 3 octal selects the 4th column while 5 octal selects the 6th row down. This points to error code 43, which means that the fault is that the out-of-balance microswitch is permanently on or the harness to it is disconnected. Since I made my repair, the Fisher & Paykel website now has a service diagnostics manual that makes it easier to read the error codes. I activated the diagnostic mode to test the out-of-balance switch. On manually activating the out-of-balance lever under the top deck, the short wash LED did not turn on, which indicated that the microswitch was not working. To get to the microswitch, I removed two screws at the top of the back panel. I could then lift up the top section with the eight wash progress LEDs and remove a screw that holds the grey control module. I then lifted the control module to reveal the microswitch, an SPST-NC type. The normally open (NO) contact that would have made it an SPDT switch had been cut off. I guess that they used an SPST-NC switch to ensure that, during assembly, the quick connector could not be placed onto the wrong terminal. After disconnecting the quick connectors, I used a multimeter to measure the resistance of the normally-closed contacts. This showed that the contacts were open and that the microswitch was faulty. Opening the microswitch revealed that the contacts had become severely oxidised after many years of service in an environment with water and steam. I made a trip to our local electronics store to purchase an SPDT microswitch, and having installed that, the machine worked again. Some time later, after we moved to a new house, it failed with error code 43 again. I knew what to do, so I purchased Washing machine microswitch repair R. W., of Mount Eliza, Vic has discovered that sealed components are needed for harsh environments, including the inside of a washing machine. At least he’s had plenty of practice replacing the failing part. He can probably do it in his sleep by now... I repaired a Fisher & Paykel GW709AU washing machine that was around 17 years old. The symptom was that it would not start. I began by downloading copies of the 96 Silicon Chip An internal view of the GW709AU out-of-balance microswitch assembly. Replacement microswitches are not available from Fisher & Paykel. Australia's electronics magazine siliconchip.com.au another microswitch and installed it. Due to a busy lifestyle, I did not realise that it was only around two years since I had first replaced it. Well, two years on and the washing machine stopped during the spin cycle. This time, the “final spin” LED and “current spin speed” LED were both flashing. On restarting the washing cycle, it would start and run then stop with the same error code. Section 10.5 of the service manual indicated that the fault could be any one of eight causes, mostly related to the machine being out of balance. One of these mentioned, “Check that the switch operates correctly and the contacts measure less than 2 ohms”. I made the mistake of thinking that, as it was not that long ago that the microswitch was replaced, it was unlikely to be the problem. I also thought this because the washing machine would start and then run before stopping. I started a cycle and lifted up the lid a bit to see what was happening without activating the lid switch. I could see that the out-of-balance lever was not being activated, but the washing machine was still stopping. This indicated that out of the eight possible causes, it could only be the microswitch at fault. I measured the normally-closed contacts and got a reading of 8MW, not less than 2W as specified. It appears that the fault was intermittent. Sometimes the switch would be closed but then incorrectly open during a spin cycle. So the microswitch was faulty once again. Opening up the microswitch, it looked OK with no apparent oxidation. So what was wrong? An internet search did not reveal a data sheet for this device. I thought this type of switch might be OK when switching high-voltage, high-current loads but perhaps was no good at switching small currents in a wet and steamy environment. I started looking for a better microswitch. The Fisher & Paykel Parts Manual lists the microswitch part number as 436597 but they no longer sell that part. The replacement is the sealed OOB (out of balance) assembly, part number 420313. That includes a different switch, bracket, lever and two-wire connectors. At ~$70, this is considerably more expensive than just a microswitch. It looks as if the switch is now sealed and requires a different bracket and lever because it is a different size. Searching for the original part number on eBay showed two sellers with photos of their microswitch that had Omron part numbers D3V-6-2C24 and V-16-2C25 on them. The Omron data sheets indicate 30mW and 15mW contact resistance, respectively. The D3V-6-2C24 data sheet also shows a graph for the micro load D3V-01 series at currents as low as 0.16mA. I think that a D3V-01 series microswitch might be suitable in this environment. But at the moment, the washing machine is working with another generic microswitch from my local store, so we will wait to see how it goes first. Next time, the solution will be to use either that Omron device or the Fisher & Paykel replacement part if the OOB micro switch fails again. I now realise why a normally closed switch was used rather than normally open. If the contacts oxidise and the out-of-balance lever operates the switch, the circuit would not be closed, and the washing machine would not stop – it would be hopping and jumping around in the laundry. With an NC microswitch, the washing machine would just stop working with a faulty switch. SC siliconchip.com.au Australia's electronics magazine June 2022  97