Model A1225 / Mid 2007 and Early 2008 / 2.4, 2.8, or 3.06 GHz Core 2 Duo processor

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Screen flickers then shuts down

Sometimes after a couple of hours, more often than not, the iMacs screen start to flicker briefly and then the computer shuts down.

It tries to reboot and then shuts down again but sometimes it just stay dead. I have to pull the plug from the socket and reconnect it again to get it to boot.

I monitor the temperatures and the only hot part was the power-part and I use smcFanControl to increase the speed of the fans. Then I can use the computer longer before it happens, and it happens less often.

It is not a recent activity, but I want to try to fix it if its possible.

Answered! View the answer I have this problem too

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Is this your machine:

Apple iMac "Core 2 Duo" 2.4 24-Inch (Al) Specs

Identifiers: Mid-2007 - 24" - MA878LL - iMac7,1 - A1225 - 2134

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Yes, that is correct. I have upgraded it to 4 GB RAM and a 1 TB HDD since I bought it.

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This could be several things but lets start with the power supply. To the right of the RAM slots are LED diagnostic lights. You'll need to remove the frame to get to them. They may have a piece of black electrical tape covering them. They should all be on before it shuts down on you. A restart at this point will help identify what's failing. Let us know what the lights show. Here's the breakdown on the LEDs:

LED #1 + LED #2 + LED #3 + LED #4 = Power available, system is powered on, video card found, and internal LCD found.

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I have been stressing it for 4 hours now but maybe when the frame is of it gets cooler. The temperatures are a bit lower than normal for this activity but I will keep at it until it goes black again. Btw, no tape on the LEDs.

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If it ain't broke, we can't fix it ;-)

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The usual phenomena when you are about to demonstrate something... Well, the frame is off so its a lot cooler, more air intake and the temperatures are way higher then usual, but still no flicker yet.

I will put the frame back. But its the LED status after a flicker/shutdown/reboot you want to know? Do I have to watch it manually as the system fails and shuts down and tries to reboot or will they stay in a informative way even after that happens?

Is there any log files that give a hint?

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There may be log files, we'll see.

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At the moment its running better than it ever has, very strange. The frame is back on, aswell as the glass and it runs a lot hotter, but still no flicker. I will post back immediately when it stops being nice and resumes its normal behavior...

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Niklas Edwall will be eternally grateful.
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