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SERVICEMAN'S LOG Samsunk – or the dishwasher that wouldn’t Dave Thompson I’ve owned many Samsung products over the years and no wonder; this South Korean manufacturer has their fingers in many pies. They’ve been around for years but more recently have become known as innovators and leaders in the field of consumer electronics, especially phones, tablets and TVs. Like many other companies, they’ve had the odd swing-and-a-miss, but in general, they make quality products. I was mindful of this when we renovated our house a few years ago and decided on some shiny new Samsung appliances for the kitchen. For the dishwasher, we chose a Samsung Waterwall over appliances made by more well-known brands that specialise in kitchen appliances. It certainly wasn’t the cheapest option, but it looks the part with its minimalist, brushed stainless-steel exterior and slick, futuristic blue multiLED display buried behind the door panel and peeking through tiny, patterned holes laser-cut into the facia. Very cool and just the thing for the modern kitchen. However, it is not without its problems. From day one, when the wash program was set and the door closed, the front display would often show all 8s instead of the time remaining. A light tap on the door beside the display usual- siliconchip.com.au ly got it back to normal. I suspected a loose connection or dry joint perhaps. We’d spent a long four months rebuilding and renovating the kitchen while cooking on a gas range, having dinner on crates and washing our dishes in a bucket. I wasn’t keen to tell the wife that mere weeks after installing the dishwasher, I’d have to pull it out again and either get it repaired under warranty or disassemble it and repair it myself. For the time being, we could live with such a minor fault; after all, its operation wasn’t adversely affected, and the display glitch only manifested itself roughly half the time anyway. I did log the fault with the relatively good online registration/warranty system and was advised by some virtual assistant to take the dishwasher to an accredited repair agent — advice that I ignored because, well, that’s what servicemen usually do when faults develop in their own gear. Besides, shoehorning a dishwasher into a 1997 MG to Australia’s electronics magazine transport it to an appliance-repair guy across town just isn’t feasible! The dirty water thickens That was two-and-a-half years ago, and aside from that small fault, the dishwasher performed flawlessly. However (there’s always a however!), a few months ago, I started noticing that the bottom rack of dishes (usually the most soiled in any dishwasher layout) were not being cleaned properly. This would happen once every ten or so washes, but over time it started happening more often, until almost every wash cycle ended up with dirty dishes in the bottom tray. I was actually becoming a bit annoyed. It’s a story all too familiar with modern appliances, conveniently failing just outside of the two-year warranty period. I messaged the virtual assistant on Samsung’s website and May 2019  61 Items Covered This Month • • • • The dishwasher that wouldn’t RF interference at the end of the rainbow Marantz 1120 amp repair Vacuum cleaner tripping RCD *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz received the same advice as before. I don’t know how they expect people to be dragging dishwashers all over town but we still don’t have the capacity to easily do that. The other option was to have a technician come out and have a look at it. Two things deterred me: one, the sheer cost of the callout (I knew I should’ve gone to appliance-repair school) and two, the guys I rang up and talked to had no experience with a Samsung Waterwall dishwasher. Perhaps these appliances were still a bit too new. Desperately seeking solutions My next stop was the good old interweb; somebody must have come across this problem before! And it seems they had; forums were ablaze with the flaming posts of disgruntled Samsung Waterwall owners. In fact, some posters were trying to scrape up support for a class-action type product recall, while others just bemoaned Samsung and everything connected with the company. Most stated they’d never buy Samsung again. Crikey! I wish we’d seen this before we bought the thing, but then again, these posts weren’t there at the time (note to self: must mend the time machine, then go back in time and choose a different dishwasher. Also maybe do something about that Hitler guy). It is worth noting that forums tend to disproportionately magnify any problems because they are being viewed through the lens of people whose first instinct is to get online and vent their 62 Silicon Chip spleen. It’s as if they are on some kind of modern-day crusade, using their collective rage to try to take Samsung down and thus salve their consumer remorse for making a poor purchasing decision. To put this into perspective, Samsung has sold hundreds of thousands of our model of dishwasher alone, yet 20 people grumbling about it in a forum can make it look like this machine is the worst thing ever made. Like I’ve always said: the best thing about the internet is that it gives people a voice; the worst thing about the internet is that it gives people a voice. I did my usual research on the web, first looking for similar problems and solutions for my model of dishwasher. When I found nothing but other people griping without offering any clues to the cause (or better still a fix), I cast my net wider into other models, and used broader and broader search terms, in a quest for anything relevant. Frustratingly, I found nothing constructive. I assumed at the time that this was because of the relatively new technology being used and the lack of repair reports filtering through to endusers via the internet. I couldn’t find any service manuals online, either. While there were plenty of user manuals available for download, they offered nothing but the usual operating advice and a basic (ie, useless) troubleshooting guide. What I needed was a full service manual. While I discovered a site advertising one for sale, it was too expensive. Given time, free service manuals must eventually appear online. In the meantime, I played around with the dishwasher’s settings and enabled some zone ‘turbo’ settings, and this, in conjunction with pre-rinsing the dishes and trying different powders and pellets, helped clean the bottom rack a bit better. Still, it rankled that I had to wash the dishes before I put them in the dishwasher. After all, it was supposed to be washing dishes for me — not the other way around (you had one job, dishwasher)! An actual fix or explanation of the cause of this problem would be nice to have. Now the dishwasher is complaining too So, that was the situation until a new fault appeared just a few weeks ago. This manifested as a grumbling noise just after starting the wash cycle; usually. I noticed this immediately since its operation is normally extremely quiet. My first thought was perhaps a pump bearing had failed, but I was just guessing; I’d need more information on how it worked to be even in the troubleshooting ballpark. But the faults were likely related. I went back to the web and once again waded through the familiar wasteland of the forums, though this time, I started seeing a link to a YouTube video purporting to show a relatively simple fix for this very problem. There was also more incidental information, so it appeared that between now and when I first started looking, a lot more people had experienced similar problems and some valid repair information was finally starting to appear. I also found a link to a free service manual, which I immediately downloaded. It was then off to YouTube to check out this ‘fix’ video. The guy in the video, who appeared to be American, described the exact problem I was having and on a very similar model. This was fortuitous because there are dozens of different models in the Waterwall range (which is typical given the different regional markets) so it was a pleasant surprise that this repair video appeared to apply to my model as well. Reinventing the (water)wheel To explain the problem properly, I have to also explain how this new-fangled Waterwall system works. In a typical dishwasher, rotating, freewheeling booms with angled spray jets in the top side are driven by water pressure Australia’s electronics magazine siliconchip.com.au and these spin beneath the dish racks and the blasting, hot and soapy water cleans then rinses the dishes. There are usually two of these rotating arms, one for the bottom rack and one for the top. It is a simple system, and while there is obviously other stuff going on (water heating, pumping, soap tray opening and drying cycles), that isn’t relevant here. In the Waterwall system, there are two horizontally-mounted ‘vanes’ sitting at opposite ends and spanning the bottom of the washing chamber; one is fixed at the far end, while the front one is mobile and driven backwards and forwards by a stepper motor. The front vane is clipped to and travels along a polished metal beam running down the middle of the chamber floor, and has a sharp curve on the edge, facing the rear vane. The fixed back vane has a series of high-pressure water outlets equally-spaced along its length, pointing parallel to the floor and aiming at the front vane’s curved surface. The idea is that water is blasted from the rear vane into the front vane, which creates the titular “water wall” as that vane traverses the chamber and this is what mainly cleans the bottom rack of dishes. There is now a video on YouTube showing this operation using three different cameras mounted in the dishwasher, which explains the process better than I can. There are two other racks in the dishwasher; one middle rack for cups and glasses and a cutlery tray at the very top, each with their own standard rotating water jet just like you’d see on any other siliconchip.com.au dishwasher. These traditional jets in my dishwasher clean those upper trays just fine; it is just the Waterwall system that is failing to clean the bottom tray properly. From my research, I discovered that if I’d gone down the more well-trodden route of having a technician come out, he would likely have gone through the Samsung-recommended protocols of swapping out a couple of pump motors, a stepper motor and gearbox, a sensor array and finally the main PCB, all at our considerable cost. This unsuccessful repair scenario was a much-repeated story posted in the various forums, and I have no doubt this would have been the case with us too. None of these ‘fixes’ would have resolved our problem. Finally figuring it out From the video, I learned that the noises I heard on cycle start were the front vane moving along its usual travel path to check nothing was impeding it before the wash cycle started. Indeed, one of Samsung’s helpful suggestions in their troubleshooting guide is to ensure that nothing is protruding through the bottom of the lower rack, as this can stop the vane moving and cause possible damage. The front vane on my dishwasher was moving OK; it just didn’t know when it hit the other end, so the poor old motor kept spinning and the gears kept slipping, causing the noise. The vane eventually gives up trying to move and just stops where it sits, explaining the noise and the lack of cleaning. So, what tells the vane to stop when it gets to the end of its travel? Simple: a magnet mounted on the vane hits a sensor mounted beneath the floor of the chamber, and this tells the motor to reverse and send the vane back to the start position. I proved this wasn’t happening by opening and closing the door just after and during the start cycle, to check on the progress of the vane. Sure enough, it hit the end and the motor kept on going if I shut the door again. Obviously, this wasn’t doing the motor or gearbox any good, so a fix had to be implemented before we could continue using the dishwasher. All the sharp troubleshooters out there will have already deduced that there are two possible causes of this fault, the magnet and the sensor. Australia’s electronics magazine Fortunately, by this time I’d found the service manual and could test the sensor (and many other parts for the system) by using codes from the book to run the different components individually, without having to waste a lot of time waiting for a cycle to complete. Having this information was well worth the hassle of finding the service manual. By holding down certain buttons and pressing others, I could initiate the vane travel test, and by placing a magnet near where the vane’s magnet would sit, I could stop it from moving any further. This proved the sensor was working, and that the magnet is the problem; however, I already knew this because of the YouTube video. The guy in that video explained that the plastic-coated iron magnet attached to the vane gradually loses its strength due to the constant heating and cooling cycles. His fix was to replace the magnet with a much stronger rare-earth or neodymium type. He simply took out the old magnet, which is mounted in a removable plastic housing, and glued a whopping great rare earth one in its place. His dishwasher then cycled perfectly, and he sat back and basked in the adoration of a grateful public. In the end, a simple repair I didn’t have a rare-earth magnet of that size in stock, so I tried various solutions, such as removing some from an old hard drive and cutting them down to suit, but wasn’t overly successful. I discovered that cutting these magnets with anything severely diminishes their strength. Putting two smaller neodymium magnets together side by side also didn’t work well, so I went looking for alternatives. Jaycar has some in various sizes, but those few with magnetic strength mentioned were only rated at most N35, which is probably not strong enough. I hit my usual go-to hardware-stores’ websites and found that both places I frequent had various magnets listed at a reasonable cost. I ended up with a packaged pair of N42-rated ‘door’ magnets, just the right size at 25 x 7mm and for the princely sum of just $25. I figured I could use one and have a spare for when the problem inevitably returns. Unlike the guy in the video, I kept the original magnet holder and simply shaped it a little to accommodate May 2019  63 the bigger magnet. I firmly tacked it in place using some of the food-grade silicone sealant that I had left over from the kitchen reno and gave it a good 24 hours before re-assembling the holder to the vane and the vane to the dishwasher. After completely resetting the dishwasher by powering it off at the breaker and powering it up again, I ran a test cycle using the magic codes. It worked perfectly, without any nasty noises and the bottom rack of dishes are now cleaning correctly. The display still glitches now and then, but $25 is an excellent repair bill, given it could have been much, much higher. Of course, the display is still a bit flakey as that is an unrelated problem. But I’m so relieved to have clean dishes again that I’m leaving that fix for another time... RF interference at the end of the rainbow D. P., of Faulconbridge, NSW went on a bit of a wild goose chase to try to track down the source of some strong radio frequency interference. It took some time but not only did he figure out where it was coming from, he also managed to shut the source down. Here is how… The Amateur Radio fraternity maintains repeaters on various bands 64 Silicon Chip (mainly VHF and UHF). These repeaters are usually set up and maintained by local amateur radio clubs and are for the use of all licensed amateurs. The idea is that one can get good communications from low-lying or other difficult locations by virtue of the prime (radio) location of the repeater. The repeaters have different input and output frequencies and are located on the best high point that the club can organise. For the higher bands, a single antenna usually serves for both the receive and transmit signals. You may wonder how that is possible. The received signal is typically tenths of a microwatt, while the transmitter output is usually 50W or more, and the frequency separation between the receive and transmit frequencies is relatively small (600kHz, in the case of VHF repeaters). The secret is cavity resonators. They have a very narrow passband, with extremely high attenuation outside of it. They can be connected in series for even better filtering. Most VHF repeaters have three or more cavities, providing a high degree of isolation between the transmitter and receiver. Other devices such as hybrid rings are sometimes also used to enhance the effect of the cavities. A few years ago, I joined the repeater committee of my local club in the Australia’s electronics magazine Blue Mountains, west of Sydney. For some time, the club’s VHF repeater had been plagued by interference. The origin of the interference was unknown, although it had been positively established that it was coming in on the antenna, and that nothing in the building was causing it. This had been established partly by monitoring the repeater input frequency with various receivers at different locations. The interference could be heard well away from the repeater. The interference consisted of bursts of a nasty rasping noise and made the repeater pretty much useless. The interfering signal was strong enough to open the receiver squelch at regular intervals, triggering the repeater, retransmitting the horrible noise. The constant bursts of noise were so annoying that few people monitored the repeater any more. One of our club members had a job as an engineer in one of the telecommunication companies. He became interested in the interference problem and connected a VHF antenna to a spectrum analyser at work. The interfering signal was plainly visible, and one of our member’s colleagues said he thought it was a pager signal, albeit grossly distorted and “chopped up”. Strangely, though, it was not on any established pager frequency; it was definitely in the VHF Amateur band. Actually, it was centred adjacent to our repeater input frequency with its sidebands regularly intruding into our repeater input passband. It was at these times that the interference occurred. I tried listening to the pager frequencies on a separate receiver while monitoring the repeater output but I was initially confused because sometimes the pager data seemed to be triggering the repeater, sometimes not. Telstra used three pager frequencies at the time. These same frequencies were transmitted simultaneously from stations dotted around the country. Signals on one of these frequencies were definitely unrelated to the interference, but the other two seemed to both be contributing to it. Eventually, by using two receivers, we discovered that it was when both of these frequencies were active simultaneously that the interference occurred. So it seemed to be some kind of intermodulation effect, but where was it occurring? It was not in our repeater, since we had established that the insiliconchip.com.au siliconchip.com.au Australia’s electronics magazine May 2019  65 terfering signal could be heard many kilometres from the repeater. I started monitoring the repeater input frequency in my car as I went about my normal activities, to try to get an idea of where the signal was strongest. The interference could be heard all over the place with varying strength with no discernible pattern, although I had the impression that elevation could have been a factor. I obtained a list of pager station locations and tried approaching several of these, however, the signal strength of the transmitters up close was so high that it swamped my receiver input and made it impossible to make any meaningful observations. I solved that problem by connecting several spare cavities between my antenna and the receiver input, carefully tuned to the repeater frequency. I could now get right next to a pager station and maintain normal sensitivity of my receiver. This approach eventually bore fruit as I was confident that I was hearing only the interfering signal, even when close to a pager station. One day, my travels took me further east than usual, and I began to receive much stronger signals than before as I moved towards the coast. Eventually, as I topped a rise to Bilgola Plateau, a flat area right near the coast, the interference came roaring in at S9+. At first, I thought something had gone wrong with my gear, but it all checked out. Maybe I was seeing the actual interference! By inserting an attenuator into the receiver input and driving around a bit, I was able to establish that the signal was coming from a tower on the edge of a public park on the Plateau. There was a hut next to the tower, and the door was open. People were working in there, so I approached them, introduced myself, explained what I was doing, and asked if they could tell me anything about the pagers. They said no, they did mobile phones, but they could give me a number for “the pager blokes”. I asked them if I could have a look at the pager gear. They showed me some very impressive rack-mounted transmitters with large heatsinks. Apparently, they were quite high-powered units. Connected to the transmitter outputs were, guess what, cavity resonators! These were not the home-brew, copper-pipe devices I was used to see66 Silicon Chip ing, but were nicely finished commercial units. I called the number the mobile phone guys had given me and spoke to a very helpful technical officer who listened patiently to my tale of woe. He said he would send a technician out to investigate the problem. When I suggested that the technician visit the repeater site to see the problem for himself, he agreed, and we arranged a time. In due course, several members of the repeater committee met the Telstra technician, complete with his spectrum analyser, on site. After a coffee break to help our new friend recover from his long drive, we connected his spectrum analyser in line with the repeater and antenna via a T-piece, after assuring him that we had disabled the transmitter! Monitoring the repeater’s receiver audio while watching the spectrum analyser screen we could plainly see and hear the interference. Our new friend agreed that it was a pager signal, and that it probably was an intermodulation product of two networks. He said he would investigate the problem. By the next morning, we were delighted to find that the interference had gone; but it returned at a lower level that afternoon. Our friend phoned to explain what he had discovered. He had found a faulty cavity at the Bilgola site and having no spares at that time, had swapped it for a good one from the Parramatta site. His thinking was that Parramatta would cause us less interference since it was shadowed from our repeater by the mountains to some degree. He had ordered a new cavity. He was right, the interference level was lower, and by setting the repeater’s squelch level higher, we were able to stop it from triggering the repeater. This was not ideal because it effectively reduced the sensitivity of the repeater, but at least we didn’t have to listen to the repeater triggering constantly. It would do until the new cavity arrived. I was curious as to why the pager units, which were transmit-only devices, should have cavities connected to them. Our friend explained that when several transmitters on similar frequencies are feeding antennas nearby, the transmitted signals from each antenna are induced into the adjacent antennas. With no cavity resonators, there Australia’s electronics magazine would be nothing to stop these induced signals being fed back into the power amplification (PA) stages of the other transmitters. These PA stages are highly non-linear (Class C), and when the transmitter is triggered, a whole spectrum of frequencies would be produced from the mixing of the transmitter output with the extra signals picked up by its antenna. This whole mess would then be amplified and anything that could get through the PA stage’s output circuit would be transmitted. These ‘dirty’ signals would be induced into the adjacent antennas as before, in turn generating a mind-boggling array of new modulation products. The cavity on each transmitter prevents this by blocking the induced signals from reaching its transmitter and rejecting any spurious outputs from its transmitter. A few weeks later, I received a call from our Telstra friend to say that he had installed the new cavity. I was able to report to him that there was now absolutely no interference, and to thank him profusely for his diligent attention to our problem. Full marks to Telstra and their staff! Since then, a tone squelch system has been installed in the repeater. A sub-audible tone imposed on the user’s audio is required to open the squelch, Preventing the repeater from being triggered by rogue signals. However, this does not prevent legitimate traffic from being subject to interference while the repeater is being used. 1970s Marantz 1120 amp repair J. W., of Hillarys, WA did a mate a favour a few years ago and fixed a fault in his trusty Marantz amplifier. Now something else has gone wrong and so it’s back on the workbench for some more surgery... A few years ago, I repaired a friend’s Marantz 1120 stereo amplifier (circa 1968). He rang last week to report another fault in the amplifier. I made a house call to check it out and found everything was working except for the phono input. There was no sound from the right channel. I disconnected the myriad cables from the unit and took the amp back to my workshop to check it out. I connected the phono input to an iPod and wired up some speakers in my workshop and found the fault was still present – no output from the right siliconchip.com.au channel speaker. I dug around in my filing system and found the circuit diagram I used last time I fixed this amplifier, about six years ago. The amplifier is built like a brick outhouse with 2mm steel plate used for the whole chassis and covers; not a bit of plastic in sight. I removed the nine screws holding the top cover in place and opened it up. I then identified the phono/select board assembly which sits vertically and plugs into another PCB behind the front panel. I connected my CRO (cathode ray oscilloscope) to the two phono input channels and I could see both waveforms from my iPod. This was difficult as the vertical phono board has the input selector switch shaft running along the whole length. I then identified the output terminals from the phono preamplifier and connected up my CRO. The left channel was OK but nothing was coming out of the right section. The circuit showed 6.8µF coupling capacitors connecting the output transistors to the selector switch, so I hooked up scope up to the driven side of the capacitors and found a good signal on both channels. I then had to try to get the board free enough to replace the faulty capacitor; I did not want to remove it completely as this involved desoldering about 10 wires. After removing the aluminium front panel and another 10 screws, I was able to move the board enough to get to the capacitor. Replacing the right channel coupling cap resulted in audio from both speakers. I decided to replace the left channel’s coupling cap as well, to be on the safe side; after all, the amp is 50 years old! I wonder if a new amplifier purchased today would last that long. siliconchip.com.au My friend had also told me that the power-on indicator lamp was not working, so I checked that and found the globe (28V 40mA) was blown. I searched in my container of small globes and found a 6V 40 mA bulb that looked like it came out of a telecom switchboard or equipment rack. The amplifier circuit showed a 390W 2W resistor in series with the globe, so after doing a bit of maths, I determined that a 1kW 1.6W resistor should allow me to use the 6V globe instead. I found a 1kW 3W wirewound resistor about the same physical size as the original and mounted it on the opposite side of the power PCB, to allow more air flow. A bit of fiddling with the new globe had it mounted correctly and working. I left the amp running for a few hours and found no sign of the replacement resistor overheating. Since it was all working, I put it back together, took it to my friend’s house and connected everything back up. While I didn’t ask for any payment, I was promised a bottle of scotch for my efforts; that’s what you call a bonus! Ducted vacuum repair G. H., of Littlehampton, SA has had problems with two different vacuum systems and both of them involved Earth leakage faults. He managed to solve both... Our house is about 20 years old. It has a weatherproof double power point on the back wall of the garage for garden appliances. About a year ago, plugging in and switching on the garden vacuum via the right-hand socket caused it to trip the Earth leakage detector in our main circuit board. Oddly, after resetting the RCD, it worked fine. And I also found that using the left-hand socket never caused Australia’s electronics magazine the RCD to trip. The fault ended up being a mass of spider webs embedded in the back of the power point. I cleaned it out thoroughly and sealed the gap in the wall around the power point, to keep spiders out. We also have a ducted vacuum cleaner inside our house which has worked well for many years. The main unit is in the garage, so it produces very little noise and no smell of musk. Then, a few months ago, as my wife pushed the cleaning hose into the wall socket, all the power to our house went off. The pipe has a metal ring which connects two terminals inside the wall socket, turning the unit on automatically. The switching is all done at low voltage for safety. I unplugged the motor unit in the garage and checked the fuse box. The RCD had tripped again, presumably due to excessive Earth leakage. Resetting it restored power to the house. I plugged the motor unit in and carefully switched on the power. The hose must have been left in the wall socket, so it sprang to life. We continued to use it without any problem until the other day, when the RCD tripped again. This time, I restored the power but left the motor unit unplugged. I first measured the resistance from the low-voltage switching wires to Earth, Neutral and Active. I was pleased to see that all readings were open-circuit, so that part was safe. The low-voltage supply comes from a 12V transformer, which powers a relay to switch the Active conductor. But the resistance between the Neutral and Earth pins of the vacuum motor was less than I expected. I measured the resistance between the Earth pin on the internal circuit board and both the Active and Neutral connections again; it was too low. I disconnected the motor from the main board. Measuring the resistance from the motor power wires to the Earthed casing of the motor also gave low resistance readings. So I began dismantling the motor carefully and measured as I proceeded. Eventually, I concluded that this leakage was due to carbon deposits which had come from the brushes. I thoroughly cleaned the carbon brush holders, then dried them before reassembly. All of the resistance readings were open circuit, as they should be, and since re-assembly, the vacuum has not missed a beat. SC May 2019  67