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SERVICEMAN'S LOG Perished belts stop a cassette deck Thirty years ago, virtually everyone had one or more cassette players or decks and cassettes were the favoured music source when you were on the move. But few are used now, so much so that I thought a recent request to fix a dual cassete deck was a joke. A few weeks ago, another April Fool’s day slipped past almost unnoticed, as is typical for me. In fact, I don’t really get into the spirit of Halloween, Valentine’s Day and other similar "celebrations". I suppose I’m being cynical but to me they seem to be just another opportunity for marketing people to exploit an occasion for commercial gain. When I was growing up, nobody I knew ever gave Halloween a second thought, other than perhaps to acknowledge it as an ancient, vaguely religious date on the theological calendar, celebrated overseas, mainly by Americans. Yet in recent years, the creeping Americanisation of our society has resulted in costumed "Trick or Treaters" going from house to house begging for lollies while in the weeks before, retail chain stores hawked cheap, Halloween-themed merchandise hoping to cash in. Kids probably have no idea what it even means. Give it a few years and we’ll probably be celebrating Thanksgiving… I can recall two rather excellent technology-related April Fool’s gags that at the time made quite an impact. The first was in the mid-nineties when PlayStation gaming was new and all the rage; one of the biggest games at the time was called Tomb Raider. I was one of many who bought the game and it was worth every penny. It was also ground-breaking in graphics, in-game physics and for introducing Lara Croft, the main character. 62  Silicon Chip This stirred up a lot of controversy in the increasingly politically-correct landscape of the times. On the one hand, it was commendable to have a female heroine, instead of some muscle-packed, wise-cracking, cigarchomping meathead like Duke Nukem and his mates. Yet on the other, she was created with some rather unrealisticallyproportioned, um, attributes, raising the hackles of feminists everywhere. Despite the backlash, the game sold millions of copies and the franchise went on to rake in gazillions of dollars for everyone involved. At the height of this fervour, one of the bigger technology magazines of the day published an article revealing a supposed "Easter egg" that players could activate within the game by tapping their PlayStation controller buttons in a certain sequence, in time with a Spice Girls hit song of the day. If they got it right, players could complete the rest of the game with Lara Croft naked! Nowadays, this might seem a little lame but back then, it was huge news as rumours had followed the game since it was released about a supposed "nude patch" built in by the developers. However, players soon discovered that no matter how hard they tried, I couldn’t get the hack to work. Er, I mean, they couldn’t get it to work. I’ll bet a lot of controllers were worn out trying, but it was all an elaborate April Fool’s joke on the part of the magazine and it certainly fooled a lot of people. In a similar vein, around the late nineties, a technology web-site pub- Dave Thompson* Items Covered This Month • Panasonic RX-FT570 dual cassette deck repair • • Currawong amplifier repair Sometimes a drill repair isn't always best *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz lished a story on how to defeat the hard-wired frequency lock on a particular model of the latest Intel processor, thus allowing it to be overclocked. The back story to this is quite interesting; the then-new Celeron and Pentium range of processors from Intel sold like hot-cakes because previous versions of these CPUs had been an overclocker's dream, with some users running the Celeron versions hundreds of megahertz faster than they were designed and rated for, just by upping the frequency multiplier on their motherboards. Until this was discovered, overclocking any CPU usually resulted in an extremely unstable system and in most cases just wasn’t worth the effort. However, experimenters soon discovered the Celeron processor, as long as it was kept cool, could be thrashed mercilessly and would remain stable and very usable at ridiculous speeds. These supposedly lower-end processors cost far less than the Pentium equivalent, yet over-clocked Celerons were out-performing their pricier Pentium cousins, something Intel hadn’t considered and certainly didn’t approve of, and were soon designing ways to stop people doing it once and for all. To prevent buyers getting more for less, the following generation of Intel processors featured a bus lock that prevented users over-clocking them by the usual means. This meant that you couldn’t increase the clock fresiliconchip.com.au quency and run the chip faster – well, you could, but the processor wouldn’t take any notice and would simply chug along at its rated speed. That is, until a respected technology-related website published a ‘howto’ on how to defeat this locking system. Apparently, owners could physically disable the lock by drilling a tiny hole into their chip at a very precise location, the process of which was clearly detailed in the article. And of course, many overclockers raced out to their workshops and got their electric drill and proceeded to drill this hole in their CPU, failing to notice the publication date of the story; April 1st. It was all an April Fool’s gag and one the publishers considered so obviously fake and so patently ridiculous that nobody in their right mind would actually go ahead and do it. Sadly, they underestimated their audience and had to quickly upload a retraction and apology in the hope that it would stop the wholesale slaughter of thousands of Celeron processors. It was an excellent prank; unless you were fooled by it! I mention all this because on April 1st last, I got a call from a guy asking me if I sold cassette tape players or more specifically, a portable cassette player with two tape decks so he could do tape-to-tape dubs. This caller siliconchip.com.au happened to sound very much like a friend of mine who is well known for his prank phone calls, such as calling and claiming to be from Inland Revenue, or the police etc. He’s gotten me a few times over the years and given this current caller’s slightly odd vocal syntax was very similar to my friend’s, I congratulated him on his inventiveness but informed him I’d busted him this time. Embarrassingly, it was a real customer with a real request and I had to eat a big piece of humble pie and apologised profusely. Once I’d explained my April Fool’s supposition, we had a bit of a laugh and got down to business. He explained that he was a choirmaster and his method of teaching the choir-members' separate vocal parts was to record his part onto a cassette tape using his trusty portable Panasonic RX-FT570 tape recorder. He’d then make several copies using the twin tape decks and pass the tapes out to other members to be learned. Hmmm, I still wasn’t sure this wasn’t my prankster friend, riding out the gag for as long as he could. The caller further explained he’d used this system for the last 20 years and it July 2017  63 Serr v ice Se ceman’s man’s Log – continued had worked perfectly until the previous day, when he had gone to record something and discovered the tape no longer turned in the drive. He remarked that he could still hear the motors whirring away inside the unit, but the tape was no longer moving in either deck. He suspected it was time to throw it into the skip and buy another one, hence his calling around the different companies in the phone book. By the sounds of it, he was not having much success. By now I was convinced this was a serious request and being relatively up-to-date with all this modern digital recording stuff, I politely suggested that perhaps he would consider modernising? Instead of tapes, people these days were using digital voice recorders, and this might be the answer. He responded with a very resounding: “No!” He told me he was "oldschool", didn’t own a computer and had no interest nor idea how any of this new-fangled stuff worked. I had to be honest and tell him that I imagined the only suitable cassette players around now would be second-hand from the auction sites, as I knew of nobody selling them new. Thinking the best way forward might be to repair his old one, I asked him a few more questions about what his recorder was doing when he pushed the play button or tried rewinding and so on. He repeated that when he pushed any of the buttons, he heard noises from within but the tape didn’t roll. He’d tried several tapes so it wasn’t a jammed cassette and the radio and speaker side of things still worked as normal. I told him that it sounded to me like a belt, capstan, tension wheel or something similar had come adrift in the transport mechanism, but given the thing was almost half as old as I am, it wasn’t all that surprising. He was under the impression that because the recorder had seen so much use over the years, it was likely time for a new one anyway. However, being a Panasonic, I knew it would have good hardware in it and suggested it wouldn’t hurt for me to at least take a look at it before he junked it, as it might be repairable. He confessed he hadn’t even thought 64  Silicon Chip about that option and became quite animated knowing that I might be able to fix it. I warned that he shouldn’t get too excited until I had a look and arranged for him to bring it around to the workshop the following day. When he arrived, he was a lot older than I’d pictured by his voice, which explained why he was not overly interested in adopting more modern technology. I did mention briefly the possibilities of digital recorders and pointed out there were cassette to digital converters available these days but he was convinced it would be too complicated. I happened to have a digital voice recorder I’d constructed a few years before and dragged that out to show him. And while he seemed quite impressed by it, he made the comment that as all his colleagues were much like him with regards to modern technology and would likely have trouble getting to grips with using something like this; perhaps it would be best to stick with their tried-and-true method. And that was fine by me; it worked for them well in the past so now all I had to do was try and get this thing working. I assured him I would try my best. Anyone who has had a tape deck of any description apart before will tell you that they are complicated devices. The concept is simple enough: a motor drives a rotating shaft which turns a spool (the capstan) inside the cassette, causing the audio tape to be dragged past the record or playback head at a certain speed. The magnetic information on the tape is read by the head and passed on to the pre and main amplification system, whether it is an internal amp as in this portable device or an external amp as in a home stereo system. However, the mechanism to do this is anything but simple. A typical cassette player usually contains a transport mechanism module and this can be unbolted and replaced as a whole if required, or sometimes individual parts can be replaced if they wear out. In this particular unit, there are two such modules, sitting side-by-side and each individually operated by its own set of buttons but driven by the same motor and belts arrangement. The core of any such system comprises the various rubber drive belts that turn the different spools, gears, capstans and wheels. siliconchip.com.au This view of the Panasonic's RX-FT570 dual-cassette transport mechanism shows some of the belts. All of the belts had perished or cracked. Considering these tape systems were designed in the days before computers, they really are a feat of engineering and design. Each of the two systems consist of dozens, if not hundreds, of tiny springs, levers, cogs, bearings, gears and pulleys, all designed to move the tape at a constant speed over the playback and record heads. If the speed was to change, the resulting distortion, including wow and flutter, would be immediately noticeable, so it is vital that the tape speed remains absolutely constant, and at the exact speed required. It wouldn’t be so bad if the tapes to be played were recorded only on this machine, as then it wouldn’t matter what speed the tape travelled at, as long as it was the same for record and playback, but pre-recorded tapes could also be played and so the playback speed must match a standard recording speed. When belts start to stretch and slip, the speed changes and problems arise. In the old days, one would simply go down to the local supplier and grab a replacement belt; you’d tell the bloke behind the counter what player you had and he would go and pick out the required belts and you’d be on your way. Of course, those days are long gone; one, you’d be hard-pressed to find anyone selling one belt, let alone a range, and two, shop-keepers with that kind of product knowledge died with the corner grocer. Opening the player was simplicity itself; none of these silly, so-called security screws, just plain old Philipshead PKs. Six held the case together, with one cleverly hidden under the siliconchip.com.au folding handle to reinforce the top section and once removed, the case split apart. Demonstrating the class and quality of this era of manufacturing were the plugs and sockets connecting speakers, antenna and battery compartment; once the plugs were separated, the front of the case came away completely, revealing the two transport mechanisms in all their glory. I could see straight away that one of the belts was lying askew and after removing a couple of retaining screws and turning the entire tape-playing section over, I could see another, smaller belt also off its tracks. I was actually happy to see this, even though I knew it unlikely I had the correct-sized belts in my bits-boxes, as it meant that replacing them would likely get this thing up and running again. It could just as well have been any one of the multitudes of tiny coil springs, leaf-springs, actuators, trunnions, levers, mechanical sensors or other impossible-to-replace parts that had worn out, fallen off or failed instead. A closer inspection revealed that all of the belts were in a pretty sorry state, with minute cracking and perishing obvious under the magnifying glass, so I decided to replace them all. As is becoming the norm these days, I hit AliExpress and there was a belt kit containing 30-odd different-sized belts, all for a couple of bucks shipped to my door. I promptly ordered the kit. The only worry was disassembling the motor and transport assembly enough to get the old belts out and the new ones in, and this is where lots of photos and parts location awareness pays off as every screw is specific to its location and purpose, and mixing them up can result in no or limited movement. It’s always tricky when there is a week or more between pulling something apart and reassembly, so those photos and even a screw map can really help. Once the kit arrived, the belts were changed and the player reassembled as per my references and the customer happy as Larry. Job done. Blaming an old lady for an amplifier mishap P. C., of Woodcroft, SA, blamed his 80-year old Mum for his inadvertent ham-fistedness when testing an amplifier. This is unchivalrous to say the least but it does emphasise how you need to concentrate when making high voltage measurements in a piece of electronic equipment. In this case it was the Silicon Chip Currawong 20W/channel valve amplifier that I had enjoyed assembling. I had been umming and ahhing for the past six months or so as to whether to build the Currawong amplifier. It interested me from the moment it was published back in 2014. After all, I had only finished the 20W Class-A amplifier and two sets of Senator speakers towards the end of 2016. But the idea kept nagging at me so I proceeded to order the PCB, front and rear panels as well as the top Perspex cover. After all, you only live once and if I didn’t do it now I probably never would. After a while the parts started to arrive and as they did I spent an enjoyable time in the shed workshop assembling the PCB. The transformer was the last to arrive and while waiting for it, July 2017  65 Serr v ice Se ceman’s man’s Log – continued time was spent building, sanding and painting the plinth. Then it was time to begin the final assembly. It all went together quite quickly and the initial testing went very well although I was a little concerned that the HT at the cathode was measuring 375VDC whereas the value on the circuit is 310VDC. I had almost 14VAC on the 12.6V heater supply for the 12AX7s also. I then wondered what my mains supply voltage was… good grief – nearly 256VAC! So much for Australia’s official mains voltage being 230VAC. We have recently had an underground mains cable upgrade and a new transformer fitted across the road. Apart from that, all the test procedures went to plan. The power LED started out red and after about 20 seconds went green and I had HT; time to plug in the valves. I chose the EH6L6 matched quads and the EH 12AX7s as they seemed a good compromise between performance and price. I fitted 10W, 5W resistors across the speaker terminals as dummy loads. It was now time for my final voltage checks. I was concentrating hard on not shorting anything and keeping in mind the high voltages present. I had the negative meter probe on the metal valve base and the other poised over the cathode of D1 ready to lightly 66  Silicon Chip touch it when, out the blue came “Yoo Hoo, Peter” in a loud, shrill voice that could only be my Mother. It scared the living daylights out of me! Almost simultaneously, there was a loud thwack sound and I now had two very black and violently blown fuses, F1 and F2. This could not be good. There was just an eerie silence followed by the request to join my Mum and wife for coffee and cake. Talk about bad timing! I thought about it, decided it might be time for a break and complied. I held my tongue and did not mention the chaos Mum had caused but just enjoyed the coffee. After about an hour I came back to the workshop for a post mortem. I worked out that as I jumped when she called out to me, I managed to short the cathode of D1 to the load end of F1, effectively shorting the 470µF, 400V capacitor. No wonder there was quite a loud thwack. From here I though it might be a good idea to test it in two steps; the HT section first followed by the LT/ control section. My first move here was to check D1 & D2 – both OK. At this point I removed the plug from CON8, leaving CON7 in place, fitted a new 1A slow-blow fuse and gingerly switched on. I was greeted by the four blue LEDs near the output transformers, glowing brightly. The HT measured 275VDC once more. No more problems here, so it was onto the LT/control section. After the LEDs faded down to nothing, I removed the plug from CON7 and refitted the plug to CON8. Doing this meant I could work the rest of the circuit without fear of getting zapped from the HT supply. Before applying power I did a quick probe around with my ohmmeter, looking for obvious shorts – I found nothing so I turned it off, fitted a new 3A slow blow F2, switched it on again and that blew the fuse again. Oh, Bother! It was time to have a closer look at the circuit diagram of the LT power supply. I then noticed CON9 which does not seem to be used or fitted on the PCB. It does have plated-through pads on top of the board which could be handy for me to apply 12V DC from a current regulated bench power supply. I removed the CON8 plug for total isolation, applied 12V DC to pin 1 of CON9 (+) and the negative to the metal frame of an octal valve base, set the maximum current at 800mA and switched on. The current shot up to this maximum and I noticed that the headphone relays were switching in and out before the current limit kicked in. Weird! At this point, I also got the very faint whiff of burning smell. Putting two and two together, I suspected transistor Q9 and this felt quite hot to the touch. I de-soldered it and tests revealed it had gone faulty, measuring about 15W leg to leg. I soldered a new one in its place and retested in the same configuration. This time everything went OK. The power LED would come on red and turn to green after 20 seconds and I had the correct supply on pins 1 & 7 of the 4093B IC. I then reconnected the plug into CON8, fitted a new 3A fuse and switched on to be greeted by… nothingness! My previous tests had proven there was nothing wrong with REG1 or any other component; which left only the W04 rectifier. Reluctantly, I de-soldered BR1 and tests showed it to have failed open-circuit, which is a blessing because if it had failed short-circuit who knows how much more damage might have been done? I did not have another in my parts store but at this point it was only about mid-afternoon on a Saturday so my local would still be open. It took only half an hour to get there and back and fitting took a few minutes at most. After I refitted everything I switched it on and everything went smoothly from there. I set the amplifier up on the kitchen table feeding an old set of surround sound speakers that I use for this sort of thing, connected my venerable Marantz CD74 CD player and was greeted by sweet and clear valve-amplified music. The total parts count of this mishap only came to one transistor and a small bridge rectifier plus four fuses, siliconchip.com.au so it was not a big issue and the time from when I heard those first startling words “Yoo Hoo, Peter” to the time it was all up and running again was only a matter of a couple of hours. It should never have happened in the first place but I kept the workshop door open that day because it was warm and I needed the airflow in the shed. Mum doesn't know anything about it! In summary, it certainly was an interesting build. I chose to upgrade the carbon resistors to metal film in the hope it might help value drift in the longer term as in the old days carbon resistors used to drift high. There was quite a wait on the two 470µF, 400V capacitors, as well as the transformer. The valves I ordered from a company called Evatco and they arrived next day. I was rather shocked at the prices of some valves. It would have been easy to spend up to $550-600 on the valves alone. This makes me a bit annoyed when, as a teenager in the mid-1970s, I had collected a huge shipping trunk full of the things and a shed load of old radio and TV chassis that I used to muck about with. Then my father decided it was his shed after all and he wanted it back; he made me load it all into a trailer and carted it to the local tip. We did not really get on that well after that. When a repair isn't the best option A. F., of Kingscliff, NSW got a reward recently for looking at a damaged electric drill and he didn’t do any repair work at all. When I read Dave Thompson’s Story about a brand new nail gun that failed after a short period of use, it reminded me of a brand new electric drill that I purchased a short while ago which failed. It eventually resulted in me receiving the most unexpected and highly rewarding gift, and I did not even have to do any repair work! This saga started when a young family member named Ron asked if he could borrow my electric drill, to install some shelves in the garage of his new home. I was reluctant to lend him this old tool, as I had used it a lot during my renovations to my first home, when I was struggling to pay off my loan and also afford the renovation costs and tools. I explained to Ron that my drill had to be used gently, due to its age. When I used it, if the body of the drill became siliconchip.com.au warm, I knew that it was time to go for a coffee break. The drill was an old two-speed model with a two-stage trigger. When the trigger was first pulled, the circuit routed the power to the brushed armature through a single power diode, which resulted in a half-wave DC being applied to the armature, resulting in a slower RPM at the chuck of the drill. Pulling the trigger all the way resulted in the diode being shorted out and full wave 230VAC being applied to the armature and field coil, and a higher RPM; simple but effective. Ron disappeared with my drill, and it was several days later that he showed up, with an unhappy look on his face, like a puppy that knows it has been naughty. He explained that my drill had stopped working. One sniff at the ventilation slots of the drill and I knew from the pungent smell of burnt varnish that he had cooked the windings on my old drill. Ron quickly explained that he would replace my drill with a new one, if I would use my knowledge of power tools to buy myself a new suitable drill, and buy a second one for him. I went off to Bunnings Warehouse, and found an Ozito brand domestic quality drill on special for less than $50. I bought two drills and gave one to Ron, along with his receipt. The next time I saw Ron, he explained that the drill that I bought him had failed and that he had bought a different one, with more power. I didn’t query Ron as to what kind of work he was doing, as I had now learnt that he was a “Bull in a China Shop” kind of worker who was not able to take a break when his tools become hot. I asked Ron if he had taken his drill back for replacement, as it had a 12-month warranty. Ron said that he had thrown his receipt away along with the packaging. He offered me his non-working Ozito, in case I wanted to remove some parts from it before it went into the recycle bin. I was curious as to what had gone wrong with Ron’s brand new drill, as there was no burnt varnish smell coming from it. I carefully opened the drill casing, and could immediately see that the “Forward / Reverse” double-pole double-throw switch had deformed for some reason and the contacts were no longer touching, to make the circuit. I was going to try to repair or replace the switch when I remembered that the unit was still under warranty. I had worked in quality control many years ago and I knew that the manufacturers liked to receive their failed products back, so that they could examine them, to find out why they had failed in actual customer service. So I carefully reassembled the drill and took it to Bunnings, along with the receipt for my drill, and asked if it could be replaced under the Ozito warranty. I was told that the drill would have to be sent back to the manufacturer for examination, before a decision could be made. Several weeks later I received a phone call, asking me to call in to Bunnings, to discuss my drill. I was told that Ozito would replace my drill but would also offer me a no-charge upgrade to their industrial quality drill, as they thought I would benefit from the additional power in their heavy duty machine. I was as happy as a motorist who is let off a speeding fine, to be offered a better unit for free. Some weeks later when I went to visit Ron, I found out that we were not allowed into the backyard, due to his construction works. He had been building a deck on the back of his house and was busy drilling halfinch holes through four-inch hardwood posts. No wonder the poor little domestic duty drills had been unable to cope! I was tempted to let Ozito know why their drill had been unable to make the grade but having gained a “You Beaut” machine for free, I thought I had betSC ter keep quiet! 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. July 2017  67