Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor

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iMac 27 2011 Black screen, no power beep, fans spin, cd drive sound

Hi all,

After trying a lot of things I'm a bit clueless.

I got a iMac 27" mid 2011. I started having blue/green stripes. So I guessed the GPU was bad and needed to be replaced. Before the new GPU came in it was already dead: black screen

I ordered a ATI Radeon HD5750 to fix the problem. After installing I still had a black screen.

  • LED 1 - On
  • LED 2 - On
  • LED 3 - Off
  • LED 4 - Off

Tried PRAM/SMC resets.

After a while I didn't get any power beeps any more. So I tried another motherboard but still no power beep.

It turns on with black screen, fans spinning and optical drive making noise. After a while the fans go full speed.

  • LCD is working fine on other iMac.
  • Got no external video output.

All help would appreciated

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I think you have a bad GPU board. Where did you get it? You need to have one that has the Apple firmware.

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Ebay. Listed as working from mid 2010 model

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Put your original GPU back in to see if the blue/green stripes reappear (good sign!) If not you have deeper issues than the GPU board to fix.

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i tried the gpu in a 2010 model and it is working...

next to gpu, logic board, lcd and powersupply working what could it be?

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1 Answer

Chosen Solution

I see the problem now! You got the wrong GPU board! You got: ATI Radeon HD 5750 1 GB, Apple P/N 661-5579 which is for a 2010 27" iMac not for a 2011 27" iMac!

Here's your choices:

  • AMD Radeon HD 6770 512 MB, Apple P/N 661-5967
  • AMD Radeon HD 6970 1 GB, Apple P/N 661-5968
  • AMD Radeon HD 6970 2 GB, Apple P/N 661-5969

Basically, the system doesn't support the older GPU.

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Thanks, thougt the 2010/2011 were supported in both imacs

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