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SERVICEMAN’S LOG This time, it's personal! Dave Thompson If I were living up to my increasingly curmudgeonly ‘old man’ persona, I would complain about the fact that nothing is made to last these days. I know that I’m just a grumpy old sod, but in my defence, things just really aren’t made the way they used to be. We’ve all read the servicing stories here detailing how people needed to swap the motor out on a 40-year-old washing machine or kitchen stand mixer because they finally wore out after all those years of faithful service. However, nowadays, we all too often hear tales of a 'smart' TV that lasts less than two years or an expensive kitchen appliance that fails after just over a year (sometimes sooner!). Most of us have experienced this. My wife has had several of those trendy fitness watches that are all the rage now. She has had two in the past few years, and both failed either physically (the flimsy straps or case breaking) or electronically (the screen failing). Those things are not cheap to buy, yet they are cheaply manufactured. There are no spares for them other than third-party products from sites like AliExpress, so essentially, they are throwaway items. Being old-school, I’ve been wearing my Tag Heuer Professional watch every day for 30 years now, and it still looks like the day I bought it. It is definitely not a throwaway item, and while it has been regularly serviced, spare parts are still available from the maker if need be (the bezel detent spring has been replaced twice). My wife now has a Garmin smartwatch, which seems to do what it says on the tin. It also appears very well-made and is as robust as those devices need to be. So, companies can do it if they want to. I feel that because 98 Silicon Chip so much of technology is here today, gone tomorrow, the manufacturers just don’t expect anything they produce to last long enough before it is essentially redundant, so they don’t care that much about repairability or even providing spare parts. In my bread-and-butter trade, computer service and repair, a particular computer brand (that always reminds me of brown sauce) became a joke for its high failure rates. So much so that my customers commented, on many occasions, that the company must have built a timer into the machines because they always seemed to fail just outside their warranty period. I’m not claiming that this company was the only one whose computers failed – that happened across the board. Honestly, their failure rates were more likely tied to mechanical hard drive reliability (or lack thereof) than a secret motherboard timer, but I’m not entirely discounting that conspiracy theory! Of course, we all know nothing is made to last these days. Everything has become consumable because technology marches on at an alarming rate. Last year’s $10,000 OLED TV is today’s $1500 bargain bin special, replaced by some new QDLED, 4XLED or ZZYZXLED models (I might have made some of those up). Moore’s Law (the idea that the number of transistors on a chip doubles roughly every 18 months) might seem naïve now, but as a product of his time, it is still valid. The increasing complexity and reduced cost of integrated circuits have greatly impacted how and what we buy and what is being created in those massive factories overseas. Despite the bad things that come from it, the beauty of all this technology and manufacturing is that relatively inexpensive consumer electronics are widely available for anyone in all but the farthest-flung reaches of the planet, even New Zealand! One of the first truly ‘consumable’ items many of us experienced was the venerable computer printer. Early printers were made like old English cars. Solid, heavy, noisy and mostly reliable. Later printers were flimsy, but at least they produced good-quality prints when they worked. However, the printer companies eventually realised they could sell the printers for less, often below cost, and make up for it by charging a King’s ransom for the ink (and sometimes other consumables). I once worked out that for a typical $100 printer, an average customer would shell out $2000 for ink over its lifetime. No wonder all those ‘refill your own ink’ businesses Australia's electronics magazine siliconchip.com.au Items Covered This Month • • • • • • A device with one foot in the grave A quick fix for a failed start capacitor Cleaning a dirty preamplifier Fixing a muffled woofer The old days of TV antennas Simple troubleshooting 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 flourished under that business model. At one point, printer ink was the most valuable product on earth by weight! Many people would buy a new printer rather than shell out for expensive cartridges. Because consumers who wanted decent colour printers had few options at the time other than ink-jet or bubble-jet printers, we all printed millions of pages with them and fed several booming industries. The problem with them is that when a 50¢ plastic piece of hardware fails, we can’t buy spare parts to repair it. Manufacturers soon decided they didn’t want capital tied up with spare parts sitting on shelves, and they’d rather us buy a whole new printer. That’s what the consumable business model became. The printer itself became the consumable and that is still the case today. It was a boon for the manufacturers, but making printers a throwaway item sure created a lot of waste! Now it is also the same with mobile phones, tablets, laptops, fridges; anything with a shelf life of less than a couple of years. Even if made available, parts are expensive and often impractical to source. It is great that the Right To Repair movement exists, but they have only made a small dent in the problem so far. If the parts aren’t readily available, we still have to take the hit and chuck the item away. There is certainly a wealth of gadgets and tools out there designed to keep us buying more. One such device is a foot sander. I don’t know the actual name of it, but you’ve likely seen these things for sale at pharmacies and big box stores. They are designed to remove dead skin from feet and prevent corns and other maladies. A motor and gearbox assembly spin the replaceable abrasive roller, and it’s used very much like a palm sander, except for feet. They are usually battery-powered and come with a charger and rechargeable batteries hard-wired inside. Some are marketed under brand names, but many are just generic and sold cheaply. Again, they have consumables to keep the cash rolling in, in the form of abrasive sanding rollers that wear out all too quickly. A cynic might think these could be made of sterner stuff and last a lifetime, but where’s the profit in that? My wife has one, of course, and it has done some work. We found a Chinese source for the rollers, so we didn’t have to pay the exorbitant prices at the local outlets. These replacements might not be quite as high quality, but considering their low cost, they work well. She went to use it the other day and had it charging as siliconchip.com.au usual. When she picked it up, it was smoking hot! She called me in, and she was right; the thing was almost too hot to hold. Not only that, it also wouldn’t turn on. Flick the switch, nada. Something was evidently wrong inside there, which meant I was duty-bound as a Serviceman to open it up and have a look as soon as possible. This is a simple device, but was it simple to open? No, it was not! Only three small PK screws held it together, but it seemed to be like one of those puzzles where nothing will come apart until some magic happens. I could separate the case slightly and see the batteries inside, but pulling the abrasive wheel end apart seemed impossible. The roller itself just popped out, but the rest of it seemed to be either glued or clipped together in a way I couldn’t figure out. A central piece needed to be removed, but it appeared to be nailed in there; I couldn’t move it at all. There were no hidden screws under a sticker or anything like that. In situations like this, the urge is to use more salt and pepper and make something move, but I thought I would break something if I did that. It seemed impossible, so I did what anyone would do and walked away to ponder the problem. A fresh set of eyes might be the answer. I returned the next day, and fresh eyes didn’t help; I was just as perplexed. I poked and prodded to no avail and, in the end, just decided to use brute force where I thought it should come apart. I figured that if it broke, I’d repair it or just get a new one; this ‘simple little job’ had turned into a real mission. Thankfully, it did come apart in the way I thought it would, and it appeared to have been made purposely that way due to the clips inside it. I was fortunate not to break any off, and I got it apart without damage. It took a lot of blue language and struggling, though; this is the curse of The Serviceman! I wonder why someone would design something like that – after all, it isn’t like they were trying to prevent me from repairing it. Or were they? Australia's electronics magazine March 2024  99 Either way, I could see the problem right away. One of the internal AA cells had vented and dumped a gloopy mess all over the PCB. I could deal with that. I had a couple of commercial, high-quality NiCad cells that I could use to replace both. The heat appeared to have been generated by a half-watt resistor in the charging circuit. It had been mounted standing clear of the board, so this was obviously by design. The board was a little scorched underneath, but I desoldered and pulled one leg and used my LCR meter to measure it, and it was still within 5% of its marked value, so I just resoldered it back in and left it. The batteries were a different story. The blown one measured about 0.1V, while the other was 1.1V. That was understandable as it hadn’t been charged, but I was going to replace them both anyway. They were connected to the PCB by the usual nickel straps many batteries come with these days. These are typically spot-welded on and are rolled to form a solderable connector. Desoldering them from the board is easy; getting them off the board was a different story! I don’t know what the military-spec construction adhesive they’d glued these cells to the board with was, but it was as hard as nails, and I feared I would have to cut the batteries off with a Dremel or similar rotary cutting tool. The board itself was single-sided, so nothing special, but it was only half a millimetre thick and very flimsy. That seems to be the modern way. This meant that if I went Arnold Schwarzenegger on the batteries with a pry bar (screwdriver), the board would break beneath it. I loaded a new blade into one of my hobby knives and set about trying to cut the dead batteries off the board. This is the sort of job horror stories are made of; super-tough glue, 100 Silicon Chip poor access and a hyper-sharp blade are a recipe for disaster. As a long-time aeromodeller, I have been using these knives since I was a boy and have many of the distinctive straight-line scars on my fingers and hands to prove it! Luckily, this time, with decades of cautionary experience, I was OK. Still, one has to be constantly careful with tools like this. A moment’s lapse in concentration can really ruin someone’s day! The batteries did have a shrink-wrapped coating on them, so I was able to cut the cells free from that and at least get the bulk of them out of the way. But that left the cement and the jackets still stuck on the board. I trimmed what I could of the leftovers and tried sitting the new cells in the same position. That worked, but it wasn’t ideal. There was no way I could remove that glue from the board without damaging anything, so I just mounted the new cells on the remains of the old glue and used a spot of gel cyanoacrylate adhesive to hold them in place. I have a small spot-welder for this type of battery work and used that and nickel strips to connect the new NiCads together. These batteries have a much higher capacity than the old, dead ones. While the charging circuit might not be optimal for them, they would trickle charge without too much bother. Also, the runtime of the repaired unit would be about twice as long as before. Now all I had to do was reassemble it and I’d be finished. Well, that was easier said than done. Trying to manipulate the three main parts back together was like trying to herd cats into a bath. I know how it came apart, but using brute force doesn’t work as well when trying to get it back together as it did when getting it apart. It felt as if doing the same thing in reverse was definitely going to break something. The designer of this thing must have worked for Reginald Perrin’s company, Bastards Inc! I spent a good while sweating and coercing it back together. I can’t imagine how those poor sweat-shop workers making these things cope with it. I suppose they have their tricks and methods (perhaps even a jig), but this was such a frustrating gadget to work on. Given its relatively low price and throwaway vibe, it seemed increasingly ridiculous for me to even bother with it in the first place. Still, that’s what a good Serviceman does. If it can be fixed, it should be fixed. I wonder if, in the future, there will be any servicemen (or women) left who will even attempt to make things right when they see something broken. I’d like to think there will be, but time will tell. I managed to coerce the parts back together and screwed the PKs back in. After inserting the replaceable abrasive wheel, I switched it on and was rewarded with a fast-­ spinning roller. I would be very careful about getting this thing anywhere near my skin, but I guess that’s the beauty industry for you! My wife was grateful to have it back, and after a few months, it is performing well and charging correctly. While this was a ‘throwaway’ item, I feel that we should be repairing as many of these types of gadgets as possible because the e-waste we humankind are generating is appalling. I would be all in favour of making things to last again, or at least making them repairable, with traditional spare parts business models returning. I don’t think much good can come of just making things to throw away, especially with toxic electronics and batteries onboard. Australia's electronics magazine siliconchip.com.au A quick dryer repair G. D., of Mill Park, Vic fixed a machine with a common fault, but the exact way it failed was a bit surprising... A few weeks ago, my daughter called to say her clothes dryer would not start. She had just finished one load, and the machine just made a humming noise when she tried to start the second. I called in the next day and sure enough, a humming noise was all it would do, so off came the back cover. The problem was immediately very obvious. It was a failed start capacitor, but the failure mode was something that I had not seen before (photo below) – it looked like it had grown a tumour! A trip to a local supplier provided a replacement, although not in the same package format. Once installed, the machine worked as it should. rest of the PCB looked acceptable, evidently having been made on a different assembly line. Not being able to identify the unit meant I didn’t have a circuit diagram. Still, it appeared to be a straightforward audio preamp with RIAA correction circuitry switched in or out. I cleaned and tinned the switch terminals, checked the switch, replaced the missing tracks with wires and reassembled it all to give it a try. Success! Everything was working as expected. In the end, an easy fix for a bad job. Fixing the muffled woofer T. T., of Bribie Island, Qld, had a friend ask him to look at his audio preamplifier, which he said was crackling and sometimes wouldn’t work at all... I agreed, and when I received the preamp, I found that it was housed in a small plastic enclosure with RCA sockets marked “Aux”, “Phono” and “Output” on the back. On the front was a switch for selecting “Aux” or “Phono”. There was no brand name or model number visible anywhere, which made me suspicious, but he assured me that although he had bought it many years ago, it had been from a reputable shop in Sydney, and it had worked fine when he bought it. Opening the case revealed a PCB supported only by being soldered to the switch terminals. When I say soldered, that was a stretch of the imagination! It looked as if coffee or some sticky, brown cold drink had been spilled onto the PCB while the factory worker attempted to do the soldering (see the photo at lower right). Three of the six switch terminals had only vestiges of solder on them, and the copper of the corresponding PCB tracks and pads was badly corroded and lifting from the board. The copper pads were just touching the switch terminals here and there. Quality control in that factory must have been on holiday that day! I had to scrub the dried residue from the board, which did away with the lifted and corroded copper tracks. The P. M., of Christchurch, New Zealand recently came across some bouncing speakers. That is, after he fixed them and they were put back into service, they came back again... A local music venue has two powered speakers for its main PA system. One failed and was delivered to my door. The problem was that the woofer was no longer woofing. I am familiar with these units, so I dismantled the amplifier module after confirming that the problem was with the amplifier and not the speaker driver. This module is not dissimilar to the one used in the 500W Class-D Mono Amplifier (April 2023; siliconchip. au/Article/15730). It uses two IRF4227 Mosfets driven by an IRS20957 driver IC to deliver approximately 500W. A common problem with these units is the output inductor that filters the switching frequency from the output. This component works hard, as all the output current flows through it. The manufacturer has supplied an uprated coil to be used as a replacement. I fitted a new inductor and tested the amplifier, and all was well. After reassembly, the speaker was returned to the customer. A few weeks later, the other speaker from the venue turned up at my door. This time, the woofer was cutting out intermittently. After a few checks, I replaced the output inductor and could not get the fault to occur again. The speaker was returned, but a few days later, it boomeranged. Once again, I could not get it to fault, but I had an idea. I had a dead module from a previous repair of another unit. At that time, I could get a replacement module from the supplier, but this time, when I checked, they didn’t have any more. So I would repair my dead module and swap it for the troublesome one. The very obviously failed start capacitor from a clothes dryer. This PCB from a preamplifier had little to no solder left on the terminals of one of its switches. The case of the sticky preamp siliconchip.com.au Australia's electronics magazine March 2024  101 I figured the older one had died because of the output inductor, so I first replaced that and then the shorted Mosfets, and to be sure, the driver IC as well. But when I fitted it to the speaker, it refused to work. I was running out of ideas, so I asked the supplier if I could send my module to him to see if he could repair it. He agreed but reported that it worked perfectly when it got to him. Like the speaker, I was baffled, and asked if he had any suggestions. He asked if I had checked the low-side bias supply that comes from the separate power supply board. This supply is roughly 12V, sitting on top of the main negative rail, and is used to switch the low-side Mosfet. It comes from a separate winding on the switch-mode transformer and is regulated by a 7812. Apparently, it is not uncommon for the legs of the regulator to fracture due to vibration from the speaker. I checked the regulator and found it was solid, but the pins on the transformer had fractured solder joints. A quick touch-up and the speaker was back in business. A couple of months later, one of the speakers was back, this time with a different fault. After running for a while, it would start to make a fizzing noise from the high-­frequency horn. These speakers are bi-amped, so they have a separate amplifier driving the horn. I only heard the fault a couple of times, but it disappeared each time I got near it. I decided that the only way to narrow down the problem was to get the other speaker and swap modules between them. The electronics in these include a preamp board and a DSP board, which handles the crossover and equalisation. I swapped both from one speaker to the other, but the fault remained with the original. I swapped the amplifier boards and let both run on test. Of course, neither of them faulted. I accidentally left them running all night; the next morning, one was not working at all. It was not the one that had the fault originally, so the failure was with the amplifier board. I swapped the board for my repaired one to save time, and all was well again. The HF amplifier on the board consists of a high-power 102 Silicon Chip The repaired amplifier module from the powered speakers. Class-D IC (TDA8954TH) mounted under the board in contact with the heatsink, plus a few other components. I suspect that IC was the cause of the noise, and it eventually failed completely. As it is an SMD device with 24 pins, I was in no hurry to replace it. Maybe next time. The old days of TV antennas S. G., of Bracknell, Tasmania was a bit shocked when he had to deal with a very messy TV installation... This happened many years ago, well before digital television; I guess it was around 1985. I was working as a contractor installing television antennas when SBS Melbourne was transferring from channel 0 to UHF channel 28. Work was coming in fast, and it was all techs ‘to the pump’ for the upgrade as many people still wanted to watch SBS. Many installations needed a total rewire, replacing the old 300W cable with newer 75W cable to all outlets due to 300W cable being very lossy at UHF (477MHz for channel 28). Some jobs were easy (one antenna to one television), while others needed much more work. Depending on the job, we would be there from an hour to maybe a whole day for bigger sites. This job was one where I thought I would be in and out real quick. How wrong I was! The customer was one of Melbourne’s big hotels/motels, with a basic MATV system that serviced the main bar, sports bar and ladies’ lounge, with another feed over to the motel part of their complex. Thankfully, the whole system was wired in what looked like good-quality coaxial cable. The problem was that none of the televisions around the hotel or the motel had much reception; what could be received was very poor quality, varying from channel to channel and television to television. It was a real mess. Where to start? First, I measured the signal at the main distribution amplifier (a KingRay DW40). This turned up trumps; I found very little signal. So, up on the roof (flat, thank goodness) to find the big VHF antenna. Looking Australia's electronics magazine siliconchip.com.au Refresh your workbench with our GREAT RANGE of essentials at the BEST VALUE. Here's just a small selection of our best selling workbench essentials to suit hobbyists and professionals alike. ALL THE REGULAR OSCILLOSCOPE FUNCTIONS IN A SMALL FORM FACTOR 2 CHANNELS SuperPro Gas Soldering Tool Kit DURABLE CASE WITH EXTRA TIP STORAGE SOLDER ANYTHING, ANYWHERE! 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Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. jaycar.com.au/workbench March 2024  103 1800 022 888 closely at it, I found the balun’s plastic cover was not installed properly and had become dislodged, sliding down the coaxial cable, allowing water into it. After a quick talk with the manager, it was decided to replace the antenna with a combination UHF/VHF antenna and replace the water-damaged coaxial cable as required. The antenna was mounted above the main office, with the coaxial cable running through the roof and down an internal wall. Having done that, I finally had a solid signal to feed into the distribution amplifier. Readjusting the gain and slope controls at the test point on the amplifier brought all of the televisions into working condition, with no crosstalk or inter-channel interference. I went around the hotel, checking the televisions as I went; the main bar still had reception problems. The Teletext wasn’t working very well; it was important as the public in the bar would want to see the sports results. The bar had sixteen 26-inch televisions, all tuned to different Teletext pages. They were all sitting on a heavyduty shelf behind the main bar. After a bit of cable tracing (wires were going everywhere, including PA and phone/ intercom cables), I found that all these TV sets were fed from one coax cable via a series of splitters. It looked like the system had grown over the years, but the splitters were all of the wrong types, and someone had used a couple of 300W four-way splitters and had made a real mess of the job. I had to rewire the lot with the correct 75W splitters. Some sets had the old-style tomb balun, with the coaxial cable direct to the screw terminals of the balun. All the televisions were fed from a single coaxial cable, which I traced back to the wall, expecting to find a wall outlet, but no! All I found was a 75W Belling-Lee line plug and socket. I needed to pull it apart to measure the signal coming from the amplifier and adjust for the signal level. The next thing I remember was getting a strong electric shock through one arm, across my chest and through my other arm. It nearly knocked me off my ladder! Sitting down, I had a short break to think about what had happened, and that’s when the penny dropped. All 16 sets were of the same manufacturer and model and likely would have been powered from a switch-mode supply. The antenna input socket would have a couple of capacitors to isolate the input antenna socket from the chassis, which usually sat at around half the mains supply voltage. I had 16 in parallel, each putting a small current into the antenna cable. In total, it was enough to pack a wallop! After fixing and replacing the coaxial cable, installing proper splitters, an isolated wall outlet, and tidying up the cabling, I was greeted with a first-class signal, no more Teletext dropouts, and a happy manager. I also installed an AC/DC isolator at the head end, and to the main feed that went to the motel wing. I ran into a similar situation later, when I was working in Mildura for a local television repair centre around 15 years ago. A customer from one of the outlying cattle stations on the other side of Wentworth called me to say her television reception had failed. The next day, I loaded up the Songbird An easy-to-build project that is perfect as a gift. SC6633 ($30 plus $12 postage*): Songbird Kit * flat rate postage Australia-wide Choose from one of four colours for the PCB (purple, green, yellow or red). The kit includes nearly all parts, plus the piezo buzzer, 3D-printed piezo mount and switched battery box (base/stand not included). See the May 2023 issue for details: siliconchip.au/Article/15785 104 Silicon Chip Australia's electronics magazine siliconchip.com.au work van with what I thought I would need: new antennas, masthead amplifiers, cable, masts, guy wires and sundries. It took me just over an hour to get to the farm gate and a further 15 minutes to the farmhouse. The television reception was woeful. The customer had several televisions around the house (four in all). The main one was a little 20in Sanyo set that had stood the test of time. Turning the set on, I was greeted with a screen full of snow. I was about to check the aerial connection when I realised that the socket on the set had failed at some point, and the customer had removed it and spliced the cable from the antenna directly to the cable from the tuner. This set (like many others) has capacitors built into the antenna socket to isolate the chassis from the antenna system. Most televisions of the era had the chassis at half mains potential. I told the customer to wait to use the television until it was repaired; it was taken back to the workshop and fixed later. The rest of the antenna system checked out OK, and the reception was restored once the masthead amplifier had been replaced. Don’t overamplify troubleshooting J. N., of Mt Manganui, New Zealand reminds us that sometimes looking for faults in the most obvious places first is the best strategy... As I am known to take a challenge with regard to repairs, a friend asked me if I could look at his Fender AmpCan 15W guitar amplifier that kept cutting out intermittently. I said yes, but no guarantees. After he delivered it, I put it through its paces with my own guitar and, sure enough, it was annoyingly intermittent (the worst faults are when they are intermittently intermittent)! Firstly, I dismantled the unit and discovered that it had an internal 12V SLA battery and could also be powered from a suitable charger. The owner lost the charger and had been trying to run the amplifier from a 15V DC power supply. I found and downloaded a copy of its circuit, wiring diagram and user’s manual. They allowed me to discover that the charger could charge the battery and power the unit separately, but not both. The external power passed through an L7815CV 15V regulator and a diode to the battery, then onto an isolating main switch. I established that the battery positive terminal was the point where the power was being lost. I immediately suspected the L7815CV voltage regulator; however, on removing it and bench testing it, it proved good! So the following diode must be faulty. After isolating the diode, I found it was not so. Where to now? Re-soldering, of course! To identify any faulty solder joint, I resoldered each point separately. And there it was, the last spot after the diode output from the voltage regulator. It just goes to show that I could have saved a lot of time by applying the simplest remedy first! Luckily, the battery was still usable. I had a used 15V 2.1A battery charger that allowed battery operation. To ensure safety for the L7815CV, I relocated it onto the large heatsink for the amplifier, as the original charger rating was only 400mA. The owner is very happy with the repair, especially as he can now use the unit cordless. SC siliconchip.com.au Australia's electronics magazine March 2024  105