Scrambled video on iMac G4

Discussion in 'PowerPC Macs' started by Grimsrud, Dec 6, 2012.

  1. Grimsrud, Dec 6, 2012
    Last edited: Dec 6, 2012

    macrumors member

    Aug 11, 2010
    I recently was able to purchase a 15" 700 Mhz iMac G4 with a broken HDD for $20. After replacing the drive and seemingly getting everything in working order, a new problem with the video on the built in display scrambling or not even starting up arose. The problem either manifests in the form of a black screen with whitish blotches moving across it at startup, or a frozen image with colored vertical lines and scrambling while running a program. The former happens when I move the computer, and can sometimes be remedied by shutting it down and then giving it a good whack/jostle before starting it up again, other times I have to open it up again and move the wires around a bit and re-insert the video cable, and the latter happens when I'm doing something that puts a heavy load on the CD drive (it's happened twice while attempting to play Diablo during a load screen). I'm pretty sure that it's either due to the monitor cable inside coming loose/moving and/or some type of signal interference from another part of the machine. How can I go about keeping this from happening? It's frustrating have the video crap out at random, or even not work at all. There must be some way of positioning/securing/shielding that video cable that will fix this issue.
  2. Grimsrud, Dec 6, 2012
    Last edited: Dec 6, 2012

    thread starter macrumors member

    Aug 11, 2010
    Here's a picture of one of the two things it does sometimes:

    It does this sometimes when I try to boot, and it did it after I tried to wake it up from sleep just about 10 minutes ago.
  3. macrumors P6


    Jan 24, 2010
    You may have damaged the connector the connects the video cable to the logicboard. It is very fragil. Have you tried using am external video adapter to see if the GPU is not at fault?
  4. macrumors 6502a


    Apr 25, 2012
    Testing with external display would help a lot. However it is either the video cable, display or the GPU. Have you tried booting in safe mode by pressing Shift -key on boot-up? If the machine works well in safe mode then I'm pretty sure it is the GPU because in safe mode GPU acceleration is turned off.

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