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Thread: Possible iMac G3 display issue?

  1. #1

    Default Possible iMac G3 display issue?

    My 500MHz G3 is starting to have a weird graphic effect on the screen in Mac OS 9.2.2, where it has some streaking on the background caused by the windows on screen. Is this normal or is something on its way out. If something is on its way out, what would you recommend checking first? Thanks!
    Looking for working: ThinkPad 755CD w/P75, IBM PC110, Macintosh PowerBook 100, Tandy TRS-80 Model 100/101/102, any Compaq SFF 286/386/486

  2. #2

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    Quote Originally Posted by Capt. 2110 View Post
    My 500MHz G3 is starting to have a weird graphic effect on the screen in Mac OS 9.2.2, where it has some streaking on the background caused by the windows on screen. Is this normal or is something on its way out. If something is on its way out, what would you recommend checking first? Thanks!
    Could be the monitor; doubt it's the GPU. Unfortunately CRTs do degrade with age.
    I use my C128 because I am an ornery, stubborn, retro grouch. -- Bob Masse
    Machine room: http://www.floodgap.com/etc/machines.html

  3. #3

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    When I had a g3 like that, the problem came and went. To be honest - and this mightn't help you because I have no clue why it happened - the issue stopped when I removed the wifi card. I have no comprehension of why that happened but it did. It seemed like the kind of thing that should be the fault of the CRT, but then further investigation pointed to circuitry on the PAV board.

  4. #4
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    The streaking is ringing in the signal, usually caused by components in the analog circuitry wearing out (most commonly capacitors.) iMac G3s are hot boxes with no fan that tend to run smokin' hot, I'm honestly surprised they survived this long.

    I would suggest recapping the entire unit and see if that sorts the issues out. If it doesn't, you're looking at some complicated analog signal debugging. I know the early iMac G3s with the tray loading optical drive had severe problems with bad capacitors, but the later slot loading models usually didn't. But the caps in those units are all now over a decade old, and have been run smokin' hot, so they're going to be worn out.

    The cathode ray tube itself could never develop smearing/streaking as a failure mode, it's all caused by the electronics that drive it. Tubes themselves can experience only a few specific failures, like the guns wearing out and causing color problems, the heater going dark which makes the tube darker, shorts in the neck guns and outgassing.

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