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SERVICEMAN’S LOG I got the power Dave Thompson The other day, something relatively unusual happened around here, which revealed a flaw in our system. For the first time in a very long time, we experienced a power cut. It wasn’t just one of those ‘oh, the power has gone off and has come back on in minutes’ cuts – it was off for many hours. I assumed some contractor somewhere had dug a little too deeply, or perhaps in the wrong place, and had put the bucket through the cable to our part of town. I fully expected things to come back online pretty quickly. After 15 minutes, I leaned across the fence to my neighbours and asked if they’d also lost power, just in case it was something in our household that had given way. Fortunately, they’d lost power too. Oh wait, that came out wrong; I mean that it wasn’t a fault specific to me that I would have to get someone to fix. Perhaps it was one of those substation explosions you hear about. I could imagine the control room at the power station, with a map of the city and bits of it going dark in sequence as the system fails. Sadly, I think that’s just movie mayhem. Either way, something had obviously happened to our supply and we could do nothing but ride it out and wait. This obviously left us dead in the water regarding our computers, my workshop, our local area network internet connectivity – pretty well everything. Fortunately, we have mobile phones, so we could at least maintain some kind of connectivity. siliconchip.com.au After 30 minutes, I bit the bullet and called our power supplier. I soon discovered that I was gazillionth in the queue for fault reporting and support, so I wasn’t going to waste much time on that. It was obviously being reported already; my whinging about it wouldn’t make much difference in the bigger picture. I also didn’t want to burn up the remaining charge in my phone battery, even though since the quakes here, I have maintained several different USB battery packs so we can charge phones. I was really caught short when the quakes hit in 2011 and we lost power for a week. Back then, my phone had only 24% charge to begin with. With no way of charging it, it soon went flat. The bad old days Not that it was much good in the early days anyway, because all the cell towers lost mains power and the backup batteries only lasted two hours. Plus, they were so overloaded that the whole system crashed. If we were lucky, the odd text might go through, but voice calls were mostly impossible. Australia's electronics magazine October 2024  89 Items Covered This Month • Unlit ruminations • Workzone MIG (metal inert gas) welder repair • Bando Technic 5D transceiver repair 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 Of course, nothing worked once the towers’ backup batteries went flat. Landlines had been severed, and while some users in some suburbs had communications, the rest of us did not. I vowed never to be caught out again. I have at least a week’s worth of battery power here now for charging phones or any other tech. As a bonus, and again, as a result of the quakes, we have gas heating and cooking, so at least we could make a cup of tea while we watch the house fall apart in the aftershocks. However, our newest gas fire, installed recently, requires electric power to run. Given that this recent power cut happened in the middle of winter, my concern was that we’d soon get very cold. We also have several heat pumps around the house to provide basic warmth in the winter and cooling in the summer but, of course, they were offline as well due to the outage. Yes, I know this is a very first-world problem and that many people, including those in so-called first-world countries, experience power loss regularly for various reasons. However, it brought back a lot of bad memories for me, to those times when we and others had no power for weeks on end, in the darkest days of our post-quakes, semi-­dystopian society where, let’s not forget, almost 300 people died. No traffic lights, no streetlights, no mobile phones, no landlines. It was a strange time. The problem was that the earth under everything in many parts of the city turned to a liquid-like quicksand (a phenomenon known as liquefaction). All the pipes and conduits and anything else under the tarmac on the roads just floated to the surface of the street. The earthquake’s strength was such that it just lifted the asphalt, circuit junctions and access covers and ruined the roads. That’s aside from breaking all the pipes, cables and whatever else was nestled inside those conduits. This, of course, plunged entire suburbs into darkness. Luckily – if there was a lucky side to it – it was February and summer, so we didn’t really have to worry about heating. But, with all the sewers broken, there were no toilets, no water, no power, no phone lines. We were cut off. I realise that many other countries had things worse. At around the same time, Haiti experienced a huge quake, which killed thousands, as did Japan, with wider-­reaching consequences. Not having power back then was a real problem. Everything in our home relied on power. My serviceman’s mind sprung into action and, as soon as the shops were open, I vowed to buy a generator. In the meantime, I had an old gas cooker and an old gas heater that used the ubiquitous 9kg bottle of LPG. One company was giving away gas (many companies did this in an effort to help, whether it was free milk, bread 90 Silicon Chip or gas), and I took my old bottle down to have it filled. Of course, it was out of date, so they wouldn’t touch it, let alone fill it. I bought two new ones from a nearby big box store and had them filled for free. I did have to queue for hours at each place, as milk, bread, petrol and gas were being strictly rationed. It really was an eye-opener as to how people behaved under duress. At least our stove and (if we needed it) heating would work. Anyway, back to our recent power outage. As I mentioned, power outages are rare here. The last one we had was seven years ago, when we moved into this place. We’d had the power off as we renovated the house, and when we put it back on, it suddenly failed. Thinking it was something we’d done, I did as much troubleshooting as possible. I could tell power was coming in from the wires, but it died at the old ceramic pole fuse mounted on the house’s bargeboards. I had to call the power company, and the guy climbed the ladder and touched the wire and it simply fell off. Easy job, I thought. But no, new pole fuses actually have to go on poles. But the pole on our back section was apparently an old pole (60 years) and not high enough. So, the pole had to be replaced and the new fuse put on top of it. Red tape holds the nation together, or so they say. It was a completely ridiculous chain of events. Anyway, that’s the last time the power went out, so it’s a rare occurrence, which is why I thought some contractor must have dug up the cable or a substation had failed somewhere. Time for the generator to shine Whatever the cause, our house was dark and dead in the water in the middle of winter. After three, I decided it was time to dig out the generator I had queued to buy 13 years ago, and fire it up. If the power was not going to be back on for hours, we’d need to get something sorted. I knew we had hours before the freezers started thawing, but I wanted to hedge my bets. Even with the generator, we’d have to be pretty careful what we plugged in; it isn’t one of those huge Detroit diesel powered ones I worked on at the airline back in the day. Two of those could power a city! Australia's electronics magazine siliconchip.com.au This one might do some phone chargers, the fridge/ freezer and maybe the TV, at a stretch. The first challenge was getting the thing out of storage in my garage. You’d think a ‘prepper’ like me would have it set up and ready to go in a purpose-­built enclosure next to the house, but no. And it is such an awkward thing to move. It isn’t overly heavy, but it is a two-person lift because there’s nowhere one person can pick it up and carry it from. It has a frame around it, but no finger or hand holds. You also cannot get a sack-barrow underneath it because it seems like something would get bent or damaged if I tried. So, it needs two people. I could drag it from under all the rubbish I’d piled on it to the garage door, but from there to the house is quite a way, so I had to involve my wife. That, of course, is a whole other column. We managed to get it onto the porch, where we could run it out of the weather and add a cable through a cracked window to power what we needed. The next challenge was firing it up. In the interest of being prepared, I have started it periodically over the years, ensuring I had enough petrol in it and even a spare can next to it should the you-knowwhat hit the fan again. The problem is, of course, that petrol loses its punch over time and this lot had been in there for a while now. I didn’t want to just tip it out, but as the tank in the generator seems to have allowed what was in there to evaporate, even with the fuel tap off and the cap tightly applied, I had to refill it with the can I had. With the tank full, it should be good for about seven hours if my calculations are correct. Mind you, I failed maths so many times at school I can’t even count! All joking aside, I was hoping this thing would start. It has a 7HP (5.2kW) motor and electronic ignition, according to the label, so I was expecting it to fire up easily. It didn’t. In the usual design stupidity that many machines seem to have these days, the pull cord has to be pulled at a weird angle off-centre from the pull starter, adding drag on the line and making it harder to start. Whoever designed these things must have been part of the company Bastards Inc. from that TV show, “The Fall and Rise of Reginald Perrin”. Saltshakers with no holes in them, gloves with just three fingers. Surely they’d look at it and think, how can we make this work better? But it appears not. I pulled on the cord a dozen times but nothing happened. With lots of blue language and gnashing of teeth, I realised I hadn’t turned the fuel tap on. I know, I know. It’s the little things that get to you. Anyway, once I opened that, with a few pulls on the cord, it sputtered into life. Boy, these things are loud! It was now sitting right outside the window, and I was rueing the fact I hadn’t built a soundproofed box for it elsewhere and ran some cabling. We might have power now, but the price to pay was the noise. A comedy of errors I still had to connect it up, which meant breaking out the extension cords. Fortunately, I know how to roll these up properly, given my years on the road in the music business. Unfortunately, the last time I used the longest of my siliconchip.com.au cables, which of course was the one I needed now, I was lazy and just gathered it up and chucked it on the garage floor. Now it was a rat’s nest, caught in everything possible on the concrete. Great, there’s 30 minutes of my life I’ll never get back. Note to self: roll the cables properly next time! I plugged everything in and fired the generator again, this time hitting the ‘power on’ button, a standard-­looking panel switch like you see on lots of equipment, similar to those on the rear of a computer power supply. This should liven up the two mains sockets provided. However, I got nothing. No power output. Hrmm, I must be doing something wrong. It’s not unusual (Tom Jones Syndrome). I haven’t used this generator other than to test it in the past, and I might need to (shock, horror) read the instruction manual. Though quite where that manual is, I don’t know. I could always hit the internet to find it. Oh, wait... The control panel has two olde-worlde moving coil meters that showed I should have 230V available from the mains socket and 12V DC from the red and black banana sockets beneath them. So the generator itself appeared to be generating. I broke out my multimeter and tested both; I got no reading from either socket. Great; I’m glad this wasn’t a dire emergency because I was really behind the eight ball here. There must be another switch or something I was overlooking. I just couldn’t see one on the fascia, so I had to go down on my hands and knees, in the noise and smoke, to try to see what was going on. Finally, I found a circuit breaker, stuck around the back, on the motor assembly. I threw caution to the wind and pressed it, and was rewarded with beeps and lights through the open window. The governor on the genny kicked in too, so it sensed there was some load on it. Why they didn’t put that breaker on the front panel is Australia's electronics magazine October 2024  91 another one of the design ‘features’ that people who never have to use these things come up with. At least I know it is there now. So we sat down and thought: what was most important? My wife works remotely and so getting our computers and internet up and running was most pressing. The fridge and freezer would stay cold for a while at least, so we decided to prioritise getting our network up and the internet back online. That wasn’t much load for the generator; it was revving like mad right outside our office window. On reflection, that was not the wisest place to put it. Just as I was reconfiguring the plugs to get everything up and running, the office light came on. I’d switched it on so I’d know when the power came back. Excellent! All that mucking around for nothing. At least I’d wrung out the generator and had shown up some flaws in my systems. Next time, hopefully I won’t be caught as short! 92 Silicon Chip Editor’s note: I wrote an article in the January 2020 issue titled “What to do before the lights go out” about preparing for blackouts and emergencies. Since then, I have purchased another inverter, a generator, extension cords, power meters, jerry cans, propane cylinders and numerous battery-­powered lights and torches. While I haven’t needed them much yet, as Dave implies, it pays to be prepared. Always put fuel stabiliser in the petrol you’re keeping for emergencies. After a year, pour it into your car’s tank and refill the can with fresh petrol (not E10; it’s hygroscopic and corrosive). If testing a generator, switch the fuel supply off and let it die so you don’t have old fuel sitting around in it for years. Workzone Inverter MIG Welder repair Several years ago, I purchased a Workzone gasless MIG welder from ALDI Special Buys. I’ve done a lot of work with this welder, which was reliable until recently. I was building a bike rack for our bikes and all was going well until I got to a particular section. The welder started running erratically, making it difficult to make a decent weld. It was a hot day, so I thought it might be overheating. However, the welder worked well again when I turned the job over. I went on to the next section of the project. It was fine as I was welding one end, but it would not weld at all when I went to the other end. I went back to the initial end, and it worked fine there, but once again, when I went to the other end, it did not weld. Then it stopped welding completely. I no longer thought it was overheating as the overheat light was not on and the welder felt cool. I hadn’t done much continuous welding on this job; had I pushed the welder much harder on other jobs, so it should have been all right. Returning from lunch, I found that the welder still did not work. It did nothing when I pressed the trigger, even though the welder was obviously running, as I could hear the fan and the power light was on. I started troubleshooting it by dismantling the handpiece. This is easy to do as there is a nut on each end. I got my multimeter and tested the microswitch and found it was working. So it was time to take the lid off and look further. The front panel is held on with three screws, one on top and two underneath. Another seven screws hold the cover on. With the cover removed, I found where the thin cable from the microswitch connects to the control board behind the front panel. I pulled the plug out, connected my multimeter to it (on continuity mode) and pressed the trigger again. Nothing happened, indicating a break in the cable between the handpiece and the welder. I then shorted the two pins on the control board and the wire feed motor ran. I laid that wire on the ground clamp, shorted the pins again, and the welder sprang to life. To replace the cable, I had to remove the clamp that holds the outer welding cable to the welder and disconnect the ground cable from the circuit board. I removed the screws from one end of the board and loosened the screws at the other end so I could raise the board to access the nut underneath it. I found some heavier twin-flex, soldered it to the end of the original cable and pulled it through the outer cable. I reconnected both ends by splicing and soldering, then Australia's electronics magazine siliconchip.com.au applied heat-shrink tubing insulation. I reassembled the welder and got back to the job at hand. B. P., Dundathu, Qld Bando Technic 5D repair I may also suffer from Dave Thompson’s “Serviceman’s Curse”. Sometimes repair jobs take far more time than was bargained for or is reasonable. I recently bought a non-working HF amateur band transceiver, as it looked worthy of restoration. It’s a brand I had never heard of, Bando from South Korea, dating to the late 1980s. I found the service manual, all in Korean, but fortunately, the schematics were all readable. As with most transceivers of that era, valves produce the output, in this case, two 6146Bs driven by a 12BY7. The remainder is all solid state. As the final valves operate with an 800V plate supply, any service work must be done carefully. This high voltage is derived from an iron core transformer via a bridge rectifier and filtered by two series 47µF/450V capacitors with 470kW balancing resistors. On inspection, one capacitor was a dead short, which put the entire 800V on the other, which had obviously blown! I decided to concentrate on the receiver side first. After removing the capacitors, I temporarily disconnected and insulated the high-voltage winding from the transformer to the rectifier. Some cosmetic problems needed to be fixed first. A power connector on the back panel was missing, and an ugly heavy power cable passed through the rectangular siliconchip.com.au hole with a home-made cable clamp. In addition, a large toggle switch had been added, which I found was used to turn off the filament supply to the 6146s. In addition, the wires to the microphone gain control were damaged. I removed the switch and associated wiring and drilled out the hole to take a proper cable clamp with a new power cable. I covered the rectangular hole with a small plate. The top and bottom covers needed a good clean-up; a repaint may be a good idea at some stage. A couple of knobs were not original, but a friend reckons he could make some to match using a 3D printer. Now I could safely turn it on to check the receiver operation. The display came up, and the tuning knob changed the frequency correctly on all bands. Connecting a signal generator, some bands appeared to work, but several were completely deaf. The band switch is of the wafer type; using contact cleaner, I managed to get all bands working except for the 28-30MHz ones. A 1µV input signal gave an excellent SNR on all but the top band in that range, which needed at least 20dB more. I ordered some replacement high-voltage electrolytics, but being impatient, I robbed three 350V capacitors from discarded computer power supplies and made up a capacitor that could handle 1050V, together with 270kW balancing resistors. That enabled me to get the transmitter working. I connected a 50W 100W dummy load to the antenna terminal and switched to Tune on the 7MHz band. Immediate success; I had a power output that I could peak with the two variable capacitors of the pi-coupler. There is also Australia's electronics magazine October 2024  93 a Drive control that tunes the plate circuit of the 12BY7, but it did absolutely nothing! The circuit diagram shows a section of a three-gang variable capacitor. The other two sections are used for peaking the receiver’s tuned circuits on either side of a low-noise dual-gate Mosfet preamplifier (Q1). The drive control operates the variable capacitor via a couple of plastic gears. On close inspection, the gears were moving, but the one attached to the capacitor shaft via a friction fit was not rotating the shaft. For some reason, it was jammed completely. It was purely fortuitous that it was stuck in a position that had the receiver working reasonably well. But to achieve maximum output power, it did have to operate. I tried all sorts of ways to move it, such as sliding the gear off and trying to rotate it with pliers, all to no avail. How about removing the capacitor and sorting out its problem? About three hours later, having used all my solder-­removing tools, including a hot air pencil, I had to admit defeat. There are many connections to the capacitor on the circuit board, and even though it is single-sided, it was tightly connected, mainly via the solid end plates. Any further attempts could have damaged the PCB, so I had to develop a Plan B. Looking at the circuit diagram, there is a 10nF capacitor (C60) from the plate of the 12BY7 to the variable capacitor. How about disconnecting it and adding an external capacitor? I had several suitable variable capacitors accumulated over the decades that I had fortunately never thrown away. Doing a quick lash-up of the connections, it looked workable, and sure enough, I could peak the drive voltage to the 6146 valves. I made a bracket from 1.6mm aluminium and bolted it to the top of the original variable capacitor which, by luck, had 2.5mm tapped holes on top. Adding a knob was a workaround solution but not a satisfactory one. It meant that the top of the transceiver had to be left off, exposing what turned out to be 170V peak-topeak at RF on the stator. That could cause a nasty RF burn! But how could I connect to the original drive shaft? One suggestion was to make up a 3D-printed gear to mesh with the one already there, but it just would not fit. Another alternative would be a couple of pulleys and a belt drive, which also looked impractical. Then, I came up with the idea of using two universal couplings. Looking at where they would fit and the angle between the shafts, it seemed a likely solution. Off to AliExpress, and not surprisingly, there are heaps of them from different suppliers for different shaft diameters. The ones in the transceiver are 6mm in diameter, so I ordered a couple for a grand total of $14. They arrived within two weeks, just after I also received a length of 6mm-diameter tubing. As you can see from the photo, it all came together quite easily. The only gotcha was having to carefully drill out one end of the 6mm coupling to 6.35mm (1/4in), as that was the shaft diameter of the 100pF variable capacitor. Tuning with the front knob is now quite smooth and the drive can be peaked accurately. Remember the two extra gangs on the capacitor? The receiver sensitivity and noise figure were quite good on all but the top band, so I decided just to peak the slugs on the coils slightly on either side of the middle of each usable band. For example, on the 40m band, I peaked L9 at 7.1MHz and L16 at 7.2MHz. That applied to all the other bands. I now have a workable transceiver with a clean 100W SSB output on all but the 10m band. After many hours of work, I decided to leave that for another day. Once the proper high-voltage electrolytics arrive, I will replace the temporary arrangement. Yes, it took a long time, but the satisfaction of getting it to work more than made up for it. SC C. K., Mooroolbark, Vic. Above: the Korean-made Bando transceiver and a close-up of its RF section. Left: the universal coupling (with the connectors unplugged). 94 Silicon Chip Australia's electronics magazine siliconchip.com.au