Model A1224 / Mid 2007 and Early 2008 / 2, 2.4, or 2.66 GHz Core 2 Duo processor

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Screen flickering: diagnosing the problem

My iMac has had problems with screen flickering for a long while and I am attempting to fix the issue. At the moment, I am trying to understand what the problem is.

When the computer is switched on, the screen operates normally until it starts to heat up. The screen will show some horizontal lines that appear randomly across the screen, which flickers. As the computer heats up further, black blocks appear and the screen starts blinking.

If I play a computer game, the flickering issue is almost non existent. If I connect to an external monitor, there is no flickering at all.

It is my thinking that the GPU and video card are working just fine but there are problems with the link between the video card at the internal monitor, which is affected by heat. But I can't figure out which part to replace.

Answered! View the answer I have this problem too

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We need to try to isolate the issue. Hook it up to an external monitor and see if the issue persists. If so then it is the GPU (which does well with a re-flow). This model also has an inverter. I have replaced a lot of inverters on this model.

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I connected the computer to an external monitor and the monitor does not flicker at all, when the iMac itself is flickering badly. So what part needs to be replaced?

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Furthermore, I am not convinced it is the inverter because the image behind the black lines are perfect clear. I would imagine the faulty inverter would affect the whole screen and not just parts of it.

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Yes the screen may be going out. But it's not the GPU.

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I have replaced the inverter and the problem was solved. It was a simple task to remove the old inverter and insert the new one. No problems at all.

My thanks to Mayer for sharing his experience that led me to this.

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John Walker will be eternally grateful.
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