Chosen Solution
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 - OnLED 2 - OnLED 3 - OffLED 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
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 661-5967AMD Radeon HD 6970 1 GB, Apple P/N 661-5968AMD Radeon HD 6970 2 GB, Apple P/N 661-5969 Basically, the system doesn’t support the older GPU.
