Display query on 2011 27" iMac A1312

[CooperBox]

I've recently bought for next to nothing (yet another) 2011 27" iMac with reported defective GPU. I've successfully resurrected several 2009 & 2011 iMac's with similar GPU fault, and all are still working flawlessly 2-3+ years later with family members.
I've just completely disassembled this iMac and carefully 'control-baked' the GPU and reassembled.
This latest iMac now displays the following:
First boot attempt showed Apple logo hanging on loading bar, typically a symptom of faulty GPU.



Further attempt in Safe mode failed. Then Restore mode gave this pattern, again typical of others I've experienced with GPU failure.



In the past I've not bothered checking system integrity by observing LED diagnostic lights. In this case I did and found all 4 LED's were ON.


One could be mistaken for thinking that all 4 LED's ON indicates a healthy system, but this is clearly not the case.
My understanding of LED #3 is:
- Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.

And LED #4, Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated.

Any constructive comments relating to this scenario are welcomed.
And NO! This iMac will not be trashed under any circumstances, not whilst it's in my hands.

 

[Nguyen Duc Hieu]

From the pictures, I guess the GPU is half-dead.
Re-baking might help revive it for a certain period of time.
I myself got bad experience of failure in rebaking iMac GPUs, (I did this rebaking at professional repair shop on their re-work station), therefore I just skip the whole rebaking thing and purchase another old GPU to replace.