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Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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iMac 2011 Randomly Restart. Graphics Issue?

My iMac keeps restarting randomly. Often just seconds after power up and sometimes after a long time. The screen simply goes black and then I hear the boot chime. I saw several topics about this issue with mid 2011 27" iMac and I don't really know what to do.

Is this really a graphics card failure that restarts my iMac randomly? (Radeon HD 6970M) Am I stupid to go and spend $250 on another one and try?

EDIT:

I've removed my GPU card

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EDIT 12-16-2017

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Answered! View the answer I have this problem too

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Please tell us what happens when you boot using (Safe Mode) by holding down the Shift key on start up.

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Boot seems to be normal. The system appear to be a little slow, for example, when I hit the lauchpad

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The GPU was a well known recall, see if your serial number matches those listed here:

https://9to5mac.com/2013/08/16/apple-ope...

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Yes, it matches! Mine is DHJQ.

Can I fix it just reballing the GPU?

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@arkcyd I've reflowed about a dozen of these with a hot air workstation and only have one failure in the last couple of years. That failure was right off the bat.

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@mayer Applying hot air right over the GPU? How many degrees and how many time?

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I do it until I see the solder flows.

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Cool, I gonna try

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I know that this is an old thread but the video card can be reflowed again. We have done this with our 9 zone SMT oven with success on 10+ iMACs. The fix does indeed work. Reballing the GPU is not required. Been working for weeks to date. The bars are gone and the machine is once again stable. Some claim that this is a temp fix but keep in mind that it likely took years after the initial purchase for this failure to surface. Also strongly blaming the caking up of the heatsink compound on the video card and CPU for these issues. We are removing the old heatsink paste / pads and replacing with the latest and high grade pads from T-Global (Taiwan) - digikey carries these in varying grades. The thermal properties is much higher than other off brands. After the process, notice how cool the back on the iMAC enclosure is as compared to before this exercise.

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arkcyd will be eternally grateful.
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