iMac 2009 High Sierra display freeze

Oct 14, 2018
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Hi folks, I really hope someone can help. The other day, out of the blue, a strange checker type pattern appeared across my screen and from then on I was unable to use any functions. I have tried running AHT numerous times but cannot get any key combinations to work (hard drive was replaced a few years ago, but even the internet based AHT is inaccessible)

The problem does not occur in safe mode, which I am using to write this. The computer is fine for a few minutes in normal mode but inevitably the same issue occurs. I have run a full AVG deep scan which found 0 threats. As long as the display was set to sleep after 1 minute the problem did not occur, but any display activity seems to cause the problem after a couple minutes. I had to manually reboot several times in order to successfully run the scan.

PLEASE HELP! I'm no computer whiz :(


Cory Cooper

May 19, 2004
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Hello and welcome.

Looks to me like a failing video card and/or logic board. Unfortunately, that model iMac is now vintage, so getting it repaired would be difficult and expensive.

You could try connecting an external display to see if you get the same issue. If so, it's the video card. If not, it's the display or the logic board.

Hope that helps,


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