Screen flickering on and off

I have an Early 2009 iMac 24 Aluminum (2.93GHz) and had it in a box for a few months, then started using it again after moving into a new house. When I powered it on, after booting up, the screen starting going black then back on, then black, then back on. Quick flashed of the screen turning off.

I randomly decided to lower the brightness down to 40% and it has not been flickering anymore. Any thoughts what the flickering is from? Surge protector? After market RAM that was installed recently? Graphics card?

Answered! View the answer I have this problem too

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Sounds like a graphics or controller issue. Connect to an external monitor. If the behavior is there it's part of the VGU/VGC, if it's gone it's a component in your internal display chain.

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Can I explore this more? I had the screen (+ other parts) off mine to replace a hard drive & to fit an SSD in the SuperDrive slot for a FusionDrive. This works well but months later I got the flicker/black outs. Sometimes it flickers to dim but usually it cycles on then black every 5 seconds or so. The external monitor is unaffected. If I gently flick the screen it comes back on until it happens again. I have an app called iStat for temps etc. & thought the issue was high temp & if I set the fan from default (which is silent) to medium (which is faster) the problem goes away. However, I now think it is the slight vibration of the fan on medium that keeps a flaky contact good. I read that soldering wires onto the screen can make connections good.

Any further thoughts would be appreciated. As everything (apart from the screen) works whilst its black, what components are involved? Can VGU/VGC intermittently fail?

Fan set to default/slow = flicker/black cycle, fan set to medium = no problem??


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Same happened for me. Lowering the brightness worked

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