- Your Toughest Job - 3 Updates
| Phil Allison <pallison49@gmail.com>: Feb 13 05:26PM -0800 Jeff Urban wrote: ----------------- > Anyway, back to the topic. Your hardest job, brainwise. ** The Gestetner machine: Back in the early 80s, I took a job in a city office that was set up as a small design and repair business. The boss designed and protoyped high end audio and carried out elaborate modifications to commercial, domestic audio gear. His name was "Allen Wright" and as I was soon to discover, I had walked into a den of Scientologists. Little did I know I was the ONLY non Scientologist or "wog' as they like to call such people. I did the real work, fixing domestic hi-fi and guitar (mostly tube) amplifiers all day. Allan did whatever he did. Various bods would pay Allan a visit, some of them were high ranking Scientologist from their "Church" up the road a bit. A real trap for the terminally gullible. Anyhow, one day a large ugly machine arrived on the spare work bench. I remember the name was "Gestetner" and it was a stencil cutter. It refused to work and had been rejected by the local service agent as being beyond repair - more on that later. Such machines are partly electronic with a high voltage/ high frequency supply creating an arc discharge that cut the special paper stencils so multiple copies could be made of a typed document. The damn thing had suddenly died and would not cut. Allan spent hours on it, day and night cos it was for his "Church" and his reputation was all wrapped up in the job. I overhead a conversation between the Grand Poo Bah and him about the agents refusal to service the beast - both reckoned it was because the manager HATED Scientologists. And why not? Having a few minutes up my sleeve one afternoon and with Allan out of the premises I took a look at the contraption. There was a pile of stencil paper near it and I fingered through intending to take a sheet. I noticed that not all looked alike - so grabbed my analogue multi-meter and probed the carbonised surface. Some of them conducted nicely and others were insulating. Faulty paper. When the boss returned I showed him what I found and astonished he set it up with a good sheet and off the dam thing went- just perfect. Soon the Grand Poo Bah arrived to see this modern miracle and Allan was beaming. He explained what had happened and how the problem was bad paper all along. Although sitting 5 yards away, my name was never mentioned. Just a tad grumpy about Allan taking full credit for my discovery, I later approached him with a request for some financial compensation - as I had saved the "Church" a great deal of money in not having to purchase a modern photo copier. I was told to write a bill for my time. I complained is was less than 30 minutes. "Then a bill for 30 minutes is what you get" - he replied. ..... Phil |
| John-Del <ohger1s@gmail.com>: Feb 13 06:23PM -0800 On Wednesday, February 12, 2020 at 7:27:04 PM UTC-5, Jeff Urban wrote: > Anyway, back to the topic. Your hardest job, brainwise. I wish I could recall most some of them, but I think I buried them in my subconscious where they would do no harm.. One that pops in my head was an old 60" Hitachi analogue projection TV, the ones that weighed about 400lbs. At first, it seemed simple: blown horizontal output. This unit used separate horiz output and high voltage output transistors. After replacing the output, it fired right up, although the raster appeared misconverged more than it should, but the new transistor was running cool at least. I connected the cable to the back of the TV to get a better look at the raster and there was a spark at the cable fitting and the TV went dead. New transistor blown. There was a leakage between the AC input and the cold ground where the cable was. I started checking those safety caps that bridged hot to cold ground, then pulled the SMPS transformer to see if it was shorted primary to secondary, but nothing was found. It was in a basement and I didn't want to haul that beast up and out to the shop, so I went back for the service manual to fight it in the basement. To make a reaaaaaaaaaaaly long story short, it turns out it was a bad deflection yoke on one of the three projection CRTs causing the ground fault. Yep, the vertical circuit was on the cold side of the chassis and the horiz deflection and HV was on the hot side. There was arcing across the gap between the vertical and horizontal output windings of one of the yokes. |
| Arie de Muynck <no.spam@no.spam.org>: Feb 14 04:39PM +0100 In this case the toughness was more in logistics than electronics... End of 1977 I designed all electronics (console and motor driver box) for the 6 mirrors above the stage of the Genesis "...And then there were three..." world tour. It controlled 12 big 24VDC motors with potentiometer feedback. Final drivers were triacs, phase control, from a 2kW 34Vac transformer output. The driver box was built in a 19" rack in a flight case, must have weighed 60 kg. Since I was the only one that could service it, the road manager had my private number. Apart from phone calls in the middle of the night like "Come here immediately" - "Where is here" - "Dallas, Texas!" (I live in the Netherlands) the system was remarkably robust. A 5 minute conversation with the local technician usually solved the problem. The toughest problem was a call "We are in Paris, the system is completely mad, everything is oscillating". I got on a plane, paid a cabdriver extra to drive through the meadows between the cows to get from the blocked highway to a secondary road, and made it to the Palais des Sports an hour before the show. They would not let me touch it, too close to the show starting. They played with fixed mirror positions. Next morning, with the tech, I checked the system. Indeed the motors moved too fast, would not position stable, stayed oscillating, one was dead. Time to start measuring. Hmm, peak motor voltages are high? DC controller rails voltages OK. The big transformer is humming a bit, and OUCH when I touch it very hot. WTF? Measure secondary - 50% too high. Measure primary - 70% too high. OK, turn off immediately. Maybe they connected the 220V single phase input to 380V? Follow the mains cable to under the stage to a big humming and very hot box. The tech first goes pale then red - it is the 3kW 115V to 220V autotransformer they had used in the USA part of the tour... Remove that box, replace one fuse, and the show can go on again. All the electronics had survived. Arie de Muijnck |
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