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Thread: Northstar Advantage - Screen doesn't display anything

  1. #21

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    Quote Originally Posted by Robuck View Post
    Ok then if you’re so sure of yourself, record a video of you being shocked by one and post it. If you don’t, I’ll just assume you’re no longer with us...
    I'm still with you and as noted in my post above I'm 100% confident I would not be harmed by a shock from the stored energy in a CRT bulb as the energy is about 1/50th of a Farmer's electric fence unit. I have been zapped by those in the past too, and its very unpleasant, especially soaking wet in the rain. So I don't go out of my way to do either, let alone put it on video.

  2. #22
    Join Date
    Mar 2020
    Location
    mosquito-y central Canada
    Posts
    6

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    Was shocked by a B&W TV CRT as a kid. It made me jump back and sat me on my ass. But I'm still here.

  3. #23

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    Quote Originally Posted by Hugo Holden View Post
    I'm still with you and as noted in my post above I'm 100% confident I would not be harmed by a shock from the stored energy in a CRT bulb as the energy is about 1/50th of a Farmer's electric fence unit. I have been zapped by those in the past too, and its very unpleasant, especially soaking wet in the rain. So I don't go out of my way to do either, let alone put it on video.
    Color tv tubes can be damaged by a dead short to the second anode. The mask is quite thin and easily bent by a sudden discharge. I've always used a 1 Meg resistor in series to limit the current.
    Dwight

  4. #24

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    I have to say that the collateral damage of an unexpected shock is something I neglected to mention even though I have experienced it myself; viz. working on a coffee machine with a folded stainless steel body, forgetting to unplug it during testing and subsequently getting a 240v AC whack to the fingertips. Very, very unpleasant. Immediate reaction: yanked my hand out of it, tore the skin on the back of my hand on a sharp folded s/s flange and had to visit the hospital emergency room for several stitches.

    The OP seems to have gone quiet...

  5. #25

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    Quote Originally Posted by JonB View Post
    I have to say that the collateral damage of an unexpected shock is something I neglected to mention even though I have experienced it myself; viz. working on a coffee machine with a folded stainless steel body, forgetting to unplug it during testing and subsequently getting a 240v AC whack to the fingertips. Very, very unpleasant. Immediate reaction: yanked my hand out of it, tore the skin on the back of my hand on a sharp folded s/s flange and had to visit the hospital emergency room for several stitches.

    The OP seems to have gone quiet...

    Yes , exactly as I mentioned in post #20, the reason I know is that I have done this myself many times and gashed my hands on sharp objects after a shock.

    Though I had two near electrocution episodes that were/are quite memorable. Both happened before I was 15 years old. In one case I had made a DC/DC converter with a pair of germanium power transistors (2N174's as I recall) It stepped up a 12V car battery to over 400V DC. I had applied the output to the end terminals of a 2 foot long fluorescent tube.

    The application was to light up a wooden hut that I had made where a friend or two would gather to smoke a cigarette , read comics etc.

    Anyway, the output of this converter had a 4 pin Amphenol tube socket, so I just poked the wires into the holes. The tube was reluctant to initially strike (I wasn't using the starter filaments), but I found if I held the connections at one end of the tube and ran my other hand along the tube's glass wall, I could get the tube to start. You guessed it, I moved that hand too far and I had both hands connected across the two ends of the tube. When that happened, the tube went out, and I was in severe pain with a muscle spasm that prevented me from letting go of the tube, in fact I was gripping it very tightly, unable to let go. And I was on my own.

    After some moments of agony I realized that although the upper half of my body was paralyzed and in severe pain, my legs were still working , I was kneeling. So I shuffled away with my legs until I managed to get the wires to pull out of the Amphenol connector (good thing I didn't use a plug and a long cable). After that experience, every other shock I received in my life, from tube radios and TV's seemed very trivial. But it made me very fearful of high voltage DC power supplies.

    I had another episode as a teenager. I used to scavenge for electronic parts a the local dump (in NZ). One time I came across a defunct neon sign transformer from a Milk Bar. Inside it I found a beautiful American made Jefferson line to 15kV center tapped transformer. It had lovely crinkle black paint and a label plate. The output terminals on big brown ceramic insulators were 7.5kV each side with the center tap connected to the transformer body. In any case I quickly figured out how to make a Jacob's ladder with wire from coat hangers. But I got a little ambitious and made the wires longer and longer. When they got to about 6 feet tall, they became unstable and would oscillate back and forth. On one occasion my head got too close and one of the wires swung to the side of my face. It arced over before it actually physically struck and that was another very painful experience , though nowhere near as bad as the 400V DC episode.

    So after these events, I think it helped me to treat high voltages with caution, but at the same time not make me too paranoid about them either. However, these voltages sources that I was messing with then, are not nearly as dangerous as the very high voltage & low internal impedance power supplies that Linesmen have to deal with, and when I see such industrial installations, at power stations and on power poles, I would never go anywhere near them, and admire the people who work with them.
    Last edited by Hugo Holden; May 22nd, 2020 at 03:00 AM.

  6. #26

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    I almost did my self in as well. I was tuning the first IF strip of a Racal tube receiver ( I loved that receiver. It had the sensitivity of the R390 without all the mechanical hardware to deal with ). It has a high frequency, 115 MHz, IF, as I recall. It is a strip of about 8 tank circuits. The last one to tune is on the plate of the mixer tube, as I recall, at 275 or 375V. With time, all of the tuning caps where too hard to turn with the recommended orange tuning stick. I was using a metal screw driver. I knew that last one was hot but it was late at night.
    Bam. It almost knocked me off the bench stool. My arm flung back, tossing the screw driver across the room. The 5 or 6 inch metal shaft of the screwdriver had gone through the sheet rock up to the handle. I was still alive but still went into shock a few minutes later and almost passed out.
    I guess we all have our stories.
    Dwight

  7. #27
    Join Date
    Aug 2008
    Location
    Burlington, VT
    Posts
    180

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    The Advantage is famous for oxidation and failure of the Molex connector bringing in voltage from the power transformer. It's at the right rear of the main board. Every one I've ever seen has developed high-resistance and localized heating. Sometimes you can even see a burned spot on the nylon plug body. You'd be well advised to pull the main PCB and inspect the underside where pins are soldered.

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