Chosen Solution
My iMac 27” 2011 recently has an issue: After power it on, Apple logo shows up with progress bar loading.It then becomes white screen for a while.Then it turns black and reboot.Repeat step 1, 2, 3.Try to run Apple hardware diagnostic program, it seems fine. Any clue what problem this could be and how to resolve it? Thanks! Tom Update (10/10/2018) Hi Dan, Here are some pictures I just took. Thanks, Tom
OK the good news first your logic board is AOK! Now the bad… Your GPU board is gone ;-{ The test forces the onboard graphics services within the CPU to run bypassing the dedicated GPU. Here’s the IFIXIT guide you’ll need to follow Installing iMac Intel 27" EMC 2429 Dual Drive Kit (HDD or SSD) it will get you mostly there. Once you get to Step32 you’ll need to finish pulling the logic board out. Carefully remove the GPU bracket and then the GPU board. Here’s the replacement GPU’s Radeon HD 6970MAMD Radeon HD 6770M You’ll need thermal paste as well as thermal pads to replace what you have.
@lovecd - For your fan issue heres the details!
Now with a better view you can see the small inductor has been pulled off!
Here you can see where it is just hanging on! Be very careful as you really don’t want to loose it
