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 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.


Ebay. Listed as working from mid 2010 model


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.


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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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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Szal will be eternally grateful.
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