> Hi!
>
> You might be interested in reading my story of an iMac repair:
>
> http://www.tervis.fidisk.fi/saveimac.html
Did you check the thermal bonding between the chips on the bottom of the
motherboard and the metal base? The "screen fragmenting" would be the
GPU overheating and the crash would likely be the CPU doing the same.
Temperature Monitor would tell you the CPU temperature.

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Mvh./Regards, Niels Jørgen Kruse, Vanløse, Denmark