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SERVICEMAN'S LOG A shockingly cute new companion Training pets, especially of the feline variety, can be difficult. However, as is common nowadays, there are likely close to a myriad of ways to help. One method is via a “pet training mat”, which emits a buzz and ‘small’ electric shock, with all the safety you would typically expect from cheap electronics sold online. We recently got a new cat (or, perhaps more accurately, the cat got some staff to look after it). This feline is as cute as a button and therefore impossible to discipline properly. While many cat owners allow their pets to walk all over the kitchen benches and scratch the furniture, we don’t. Footprints on work surfaces and shredded mattresses and armchairs may well be part of the ‘joy’ of cat ownership, but we have always deterred our furry housemates from this behaviour. We’ve used several training methods over the years, the most technological of which was a slightly modified version of the Silicon Chip “NickOff” Bad Cat Deterrent (October 2012; siliconchip.com.au/Article/502). We found this worked for our cats at the time. However, they eventually got wise to it and ended up blatantly ignoring it. They would jump onto the cooktop and bench, to either drink out of the sink (their expensive cascading water fountain is obviously not good enough!), or scavenge their share of the roast we’d just eaten for dinner. While we’d managed to train all our cats, past and present, not to do this with a combination of water squirting bottles, sticky tapes, deterrent sprays and electronics, the new addition did and went where it liked. When the older cat saw this, his old habits started creeping back in. I’d long-since repurposed the NickOff for another project. But while I was 70 Silicon Chip browsing for parts to build another one on AliExpress, I spotted a possible solution: electronic pet training mats. These seem to be a hot product these days, both on local and international shopping sites. I was aware of such devices, but in the past, I was put off them because the one I saw was not user-friendly and a bit too aggressive in operation. Admittedly, it was designed for a medium-sized dog, but even on the ‘low’ setting it still delivered what I considered a nasty shock, out of proportion to the ‘crime’ of the dog sitting on the owner’s favourite chair. The mat or sensor part of it was also rigid, prickly to handle due to embedded wires tracks and hard to clean. I’ve never been a fan of giving electric shocks on purpose, having suffered a few ‘good ones’ over the years. Because of this, I have some empathy and a natural aversion to deliberately shocking anyone (or anything). I especially despise those ‘joke’ shockpens and cigarette lighters that were all the rage at one point; I don’t think lighting someone up deliberately is funny at all. I can’t recall seeing anyone blitzed by one of those things rolling on the floor laughing. Mostly they just look annoyed… Anyway, I figured there must be some better training mat options available these days, so I went online to check. The modern versions are inexpensive and sized for different pets, with adjustable shock levels and more Australia’s electronics magazine Maggie Thompson Items Covered This Month • • • • The cat in the mat Hot water system repair Yamaha CR-1020 restoration Mitsubishi ABS pump repair *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz flexible, easier-to-manage sensor mats. I found similar products for sale at local pet shops, but at significantly higher prices. The pitfalls of buying online I’m not a cheapskate, but I do object to being gouged by local sellers. The typical reason thrown about for exorbitant mark-up on just about everything imported into New Zealand is “shipping costs”. That excuse may have washed fifty years ago, when nobody really knew the true cost of goods, but these days everyone knows that it doesn’t justify the prices many local sellers try to charge. So it is no wonder that buying from overseas vendors is increasingly popular! But there are challenges to ordering online. So many products look very different when they arrive from the often-doctored pictures on vendors’ sites. The benefits of buying locally are obvious; stores typically have what you want, have regular sizing and naming conventions throughout product ranges, and you can always take something back and (typically) get a refund or a replacement if necessary. Sending anything, especially something of relatively low value, back to an overseas vendor is usually neither practical nor financially feasible. In practice, I shop locally for some items and use overseas vendors only when this makes financial sense, or if siliconchip.com.au a job isn’t time-critical. I’ve made hundreds of online trades for all manner of goods, generally from China and the USA, and while I have had mostly positive experiences, there have been some hiccups. I purchased several cameras from China only to be disappointed. One, a GoPro-style action camera, claimed to be able to record video at 4K resolution (3840x2160 pixels) and 60 frames per second (fps). This is ostensibly backed up by the words 4K emblazoned across the front of the case. But my attempts to record anything with it higher than 720p (1280 x 720 pixels) and 25fps resulted in unusable video. It’ll record at 4K, but only at around 1fps. If a local retailer advertised and sold such a product, their shop would be razed by a pitchforkand-torch-wielding mob. But online vendors will happily hawk this and similar products with the knowledge that there’s little we can or will do about it. Another much more expensive action camera I bought online last year (I was learning!) works much better, but still had problems. It will record at 4K and 60fps and has remote control via app, Bluetooth and WiFi, among others. But the battery went flat overnight, even when the camera was switched siliconchip.com.au off. Having to charge it for hours before every use was a royal pain in the lens cap. When I looked into this, other buyers had the same problem, and a firmware update was apparently the answer. I eventually found and downloaded the firmware. The update resolved that issue, but it was a lot of extra work when it really should have worked properly in the first place. As always, it comes down to “caveat emptor”– buyer beware – particularly with more significant purchases. Bringing the felines back in line Anyway, because of the relatively low price of these training mats, and with a lack of other ideas, we ended up buying two small pet training mats from AliExpress. When they arrived a few weeks later, the hazards of online shopping were once again apparent. While the mats were pretty much as advertised, their construction is what one would expect from such a cheap product. Only one of them arrived in working condition. The mats are powered by three AA cells; I hope they do not chew through them too quickly, as that could get expensive. If push comes to shove, I’ll modify them to run on one of the dozens of spare plugpack power supplies I have taking up drawer space in my workshop. But before fretting about that too much, I needed to fix the broken one. The mat’s controller is a sausageshaped plastic housing with a flattened bottom that sits along one short edge of the rectangular mat. It has a threecell battery holder with a removable lid, and a single button on the top to switch the power on and off when held down. Short presses cycle through the Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column? If so, why not send those stories in to us? We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. Australia’s electronics magazine October 2019  71 three shock settings: low, medium and mad scientist. This is indicated by three small LEDs. There is also a built-in piezo buzzer that chirps when the button is pressed and quickly sounds multiple times if the sensor pad detects anything. The pad resembles a large, flexible-plastic thin-film PCB with closely-interlocking printed silver tracks. Briefly bridging the tracks results in a warning alarm, but no shock; if contact is maintained for more than a few seconds, a shock is delivered through the tracks at the level selected. I’m too chicken to put my hand on it, but I did bridge the tracks with a short length of hook-up wire and there was a frankly unnerving amount of crackling and popping at the connections, even on the lowest setting. There also appeared to be an undocumented feature; a vibration sensor in the controller triggers the warning beeps (but not the shock) when movement is detected. Even lightly bumping the bench sets it off. the bottom of the controller. The two moulded halves then came apart. The electronics look surprisingly comprehensive and well-made, with a host of SMDs and a couple of those blob-style COB (chip-on-board) ICs on the board. Cloth insulating tape covered some of the components on the ‘hot’ end of the board, and initially, I left that in place. The circuitry was more complex than I expected to find, and with PCB component soldering looking good, my expectations of an easy fix might have been misplaced. I found that the two HV output connections between the mat and the PCB were just stripped-bare hook-up wires, flattened out at the ends and clamped onto ‘terminals’ on the mat between the two halves of the case. A screw through the centre of each terminal ensured a solid connection. I don’t consider this to be a particularly elegant solution, but it’s probably effective as long as the contacts are not disturbed too many times by repeated disassembly. I wasn’t sure how rugged the sensor tracks were. They appear to be made from conductive silver paint, screenprinted onto the clear plastic mat; scratching through a track at any point would break its continuity. While one of the PCB wire-to-pad connections might have been where things had failed, my gut feeling was that while basic, the contacts should be OK. To take the PCB out, I had to remove a couple of small hold-down screws. I also needed to release the positive battery terminal, which clips Fixing the obvious fault Disassembly of the faulty mat was easy. Thankfully, there were no dumb anti-tamper fasteners; just eight small, cross-head PK screws to remove from 72 Silicon Chip Australia’s electronics magazine siliconchip.com.au into a moulding in the top half of the controller and has a metal tongue that extends down into the PCB cavity below, where it attaches to a solder pad on the ‘input’ end of the board. After removing the PCB screws, I turned the unit over to see how that positive battery terminal should be removed, and the PCB fell out onto the workbench. I was reasonably sure the battery terminal should be soldered in, but a look under the magnifier revealed no solder on it at all. There was a corresponding blob of solder on the PCB though, with the shape of the tongue embedded in it. It looked like it had been pushed into hot solder but had never been physically connected. Thinking that it might be designed as a push-fit, for ease of assembly, I opened the other working mat to check. That mat’s positive terminal was properly soldered in. I sat the PCB back in the dead one, cleaned the blobbed solder from the pad and tinned and re-soldered the tongue. A quick (and very careful!) check with batteries fitted showed this resolved the problem. Reassembly was just as easy, though I took care around those fragile-looking contacts. How the mat passed QA checks (if any) is anyone’s guess, but it’s a good example of why buying online can be problematic. Someone who isn’t afflicted with the Serviceman’s Curse would have probably just binned the mat and taken the hit. You’ll be pleased to know the cats have come to no harm but very quickly learned not to walk on the bench. They now run off in every direction at the mere sound of those warning beeps! Hot water system repair A. K., of Armidale, NSW, had a solar hot water system installed in 2010. It worked well for years but recently went on the fritz and he had to fix it... Periodically, I check the various temperature readings on the Solastat controller, more out of interest than any other reason. One sweltering day last summer, I noticed that the solar hot water controller was displaying the fault code “SSd” instead of the roof sensor temperature. I checked the manual and “SSd” stands for “Smart Shut Down”, where the system idles in case of a shorted or open sensor or cable wire. This fault can also be displayed when the temsiliconchip.com.au The Solastat temperature sensor, shown above, was repaired by replacing a single NTC thermistor within it. perature sensor is outside the specified temperature range of -40°C to +150°C. Upon further inspection, I found the roof sensor or cable was open circuit. Luckily for me, it was late afternoon so the corrugated iron roof had time to cool down from its peak temperature on that 33°C day. I went up onto the roof to remove the sensor from its housing and noticed that very little sealing compound had been used. I decided to cut the sensor from the cable, leaving 10mm exiting the sensor. I probed these wire stubs with my multimeter and found that the sensor was open circuit. The temperature sensor was potted in a small steel case. I picked away at the filling until I reached the sensor, a small beaded glass device with no visible markings. The user’s manual didn’t give any information as to its type. I went onto the web and fortunately, Senztek (makers of Solastat controllers) have various manuals available for download from the website. I found an installation guide with a table of NTC sensor resistance readings at various temperatures. It specified a value of 10kW at 25°C. Further web searches revealed an Australian site selling replacement 10m cable with roof sensor to suit Solatstat controllers, including free thermal paste and joiners. Tempting! But fortunately, I already had some 10kW NTC thermistors which followed the temperature curve of the original sensor quite closely. The next day, I removed all the filling from the old sensor housing and replaced it with my new NTC thermistor. I used hightemperature epoxy putty to hold it in place and then re-soldered the sensor to the controller cable, adding two layers of heatshrink tubing for weatherproofing. Where the sensor cable exited the corrugated iron roof was utterly devoid of any sealant and as it was another hot day, I decided to fix that later, in the cool of the evening. So I dropped down to my local electrical distributor and purchased a cable gland. Australia’s electronics magazine Back on the roof that evening, I Installed the cable gland in the roof, through which the sensor cable now ran. I smothered the sensor’s metal case with silicone-based thermal paste and then slid the refurbished sensor unit into place. Finally, I used some neutral cure silicone sealant to secure the unit into the solar heater housing and prevent moisture ingress. It has been nine months now since the repair and my new sensor has not missed a beat. The replacement NTC thermistor sensor I used cost me $3 while a replacement cable with sensor would have cost $65 and that’s not including labour. I figure it was a job well done. Yamaha CR-1020 receiver repair/ restoration R. A., of Melbourne, Vic, decided to restore a retro amplifier to its former glory by fixing a few small faults which had developed over its many years of use. This is how he did it… The Yamaha CR-1020 is a chunky receiver from the late 70s. It’s powerful for its day at 80W per channel with 0.05% THD, both channels driven. It incorporates an excellent FM tuner. It originally cost $895, at a time when a base Holden HZ sedan started at $2150. I snapped up this mint-condition receiver in 2014 for $400. It has given good service ever since. These now sell in the USA for well over $1,000, which prompted me to get to work fixing mine. It had a few minor niggles: none of the lamps behind the fascia worked and the back panel switch that couples the preamp/tuner to the power amplifiers was scratchy. Working the switch a few times helped, but I prefer a permanent cure. Its timber case was also damaged in transit, on a lower front corner. Opening it up, I found all five fascia lamps open-circuit. These “grain of wheat” lamps are nominally 12V/60mA. Four are located behind the three meters, connected in series/ October 2019  73 parallel and powered from a 19.23V DC rail. The fifth is mounted on the tuning dial pointer and runs from a 9.68V supply. The reduced rail voltages were intended to prolong the life of the lamps. The subtle glow also imparts an air of sophistication to the unit. Googling revealed that it is common for these lamps to all fail, and that plenty of replacements are available, both LEDs and incandescent. Oddly, all four lamps in a series-parallel circuit can fail; if one goes opencircuit, you would expect its parallel lamp to then fail, disconnecting the other two from the supply. But somehow, this does not happen. I ordered some replacement incandescent lamps and then checked the supply voltages. The 19.23V rail (shown as 19.6V elsewhere in the circuit diagram), which also drives the speaker protection relay, measured just 13.5V. I suspected a dud filter capacitor. My DSO showed significant ripple on this rail. Clipping two 100µF caps across it drove the reading up to 17.5V (with a low mains voltage of 227V), while a 2200µF cap increased it to 19.2V. So I was pretty sure that the original filter capacitor had failed. While doing this testing, I also noticed that the speaker relay was pulling in with a very soft click, but with the larger capacitor added, the click was restored to its normal, strong sound. The replacement lamps arrived and fitting the new meter lamps was fairly straightforward. But the dial lamp was more tricky. It uses a Heath Robinson arrangement of articulated nylon arms which keep the wiring from the dial lamp out of the way as the pointer tracks across the dial. I undid the two Philips-head screws that held the sliding assembly together, gently pulled it half way open without disturbing the dial cord, pulled out the old lamp, inserted the new one and put everything back together. With a temporary capacitor in place in the power supply, I powered the unit up. The four meter lamps looked good, but the dial lamp only glowed dimly. It was only getting 4.3V due to the higher current rating of the new lamps (12V/70mA). The dial lamp has a 180W dropping resistor in series, while the four meter lamps are fed from a low-impedance source. I found that adding a 560W 1W resistor across the 180W resistor gave about 10V across the dial lamp and an acceptable level of brightness. I then turned my attention to the low 19.23V/19.6V rail. There is an apparent oddity in the circuit diagram, The internals of the Yamaha CR-1020 amplifier, with the power supply circuit diagram shown mispelled above. You can find more details on this amp at http://www.mcqart.com/cr1020/ and http://sportsbil.com/yamaha/cr-1020-om.pdf 74 Silicon Chip Australia’s electronics magazine siliconchip.com.au in that this rail feeds into diode D1, and you get 20.8V at its cathode. How does this work? It’s because there is so much ripple on the 19.6V rail that its average voltage is much lower than its peak voltage. A 1000µF capacitor at D1’s cathode means that the voltage on that side is much smoother and closer to the peak voltage. This was done on purpose, so that the speaker protection relay drops out fast when mains power is removed. This avoids nasty speaker thumps as the amplifier rails decay after switchoff. Diode D1 isolates the larger cap from the 220µF unit and stops it from prolonging the relay holding time. I think that the high ripple current the 220µF capacitor is subjected to by this arrangement is the reason it failed. So I replaced it with a more robust 330µF/50V unit. Accessing the underside of the relevant PCB would have been a major undertaking, so I removed the dud capacitor and soldered the new one across the wire-wrap stakes which connect to the supply rail. Next, I decided to fix the coupler switch. Access to it proved basically impossible, so I simply gave it a good spray with isopropyl alcohol, which appeared to do the job. I fired the amp back up, and it all worked as expected. With 237V AC mains, the output of the diode bridge was 19.0V DC, which is about right (the original specs were for 240V mains). The speaker relay pulled in firmly after its three-second delay, with its subsequent release appearing to be simultaneous with mains power switch-off, and no thumps were heard from the speakers. siliconchip.com.au I then checked the quiescent current in the power amplifiers. Working carefully, as a slipped prod can cause mayhem, I compared the test point voltages against the specification of 10mV±1mV. Both channels rose to about 14mV, so I carefully adjusted the trimpots to get 10.0mV. With everything working well, I turned my attention to repairing the damaged veneered plywood sleeve. I dripped water onto it over more than a week, to get it to swell back out, then I sanded it and applied ‘plastic wood’. More sanding, then the application of a dark stain and finally coats of Gilly’s dark restoring polish produced a remarkably good result, as seen in the photo of the restored unit below. The quality and labour that went into this receiver is a tribute to its makers. The complicated electronics (with 109 transistors) has worked well for over 40 years, indicating a great design and execution. The cadmium-plated chassis still gleams like new. The newly-polished timber sleeve still looks great, and the sound is still excellent. Mitsubishi Lancer ABS pump motor repair R. H., of North Sydney, NSW had a frustrating experience where a professional repaired the ABS (anti-skid brake) unit from his car twice, and it quickly failed again both times. He had to open it up to fix it properly himself… On taking my Lancer for a service, the mechanic advised me that the ABS light was on and a scan revealed error code 116 (low voltage at the hydraulic pump). A better description might be “open circuit hydraulic pump motor”. Australia’s electronics magazine A new ABS unit would cost over $3000 plus fitting. I then found out about a business which fixed ABS units. All I had to do was take the unit out and then for $350, they would service it. After which, I had to re-install it and bleed the brakes. All went well after re-installation, with no ABS light showing. The trouble was, after about five months, the light switched on again. As the unit was still under warranty, I went through the same process again. But after re-installing it, the ABS light stayed on. A scan showed the same error code 116, and it could not be cleared, so I gave up for the time being. Shortly after that, I found a video on YouTube showing how to fix this ABS unit. It appears that quite a few ABS units in various vehicles have the same problem. This time, I decided to do the whole job myself. So out comes the ABS unit once again, and following the steps on YouTube, I managed to isolate the motor from the valve body. I then put an ohmmeter across the motor’s terminals and it showed an open-circuit reading. On taking the motor’s case off, I found a brush hung up in its cage. It had to be gently massaged with fine sandpaper to give clearance between the brush and cage, so that it could move up and down easily. I gave the same treatment to the other brush. On re-assembling the motor and applying power, the motor hummed away – good! Next, I had to re-assemble and re-install the ABS unit, then bleed the brakes. The ABS light remained off; wonderful! It has remained this way for a couple of years now, touch wood. I don’t understand how this problem arises. Was the retaining spring behind the brush too weak to keep it seated on the commutator? What caused the brush to lift off the commutator in the first place? Editor’s note: perhaps the car hit a big pothole which lifted it off briefly, and it got stuck. One person on a web forum reported that he hit his ABS unit with a hammer, with a block of wood between the hammer and the valve body. It sounds a bit Heath Robinson but in hindsight, having observed the problem firsthand, it may just work; the impact could re-seat the brush back onto the commutator. SC October 2019  75