I have two identical iMac 27" 2011 that I upgraded to i7-2600 and K4100M. One worked out well, but the other will not boot with the LCD screen plugged in. I was able to get three logic board lights and SSH in with the screen off to flash the GPU, but once I plug the LCD in, it will not boot. I see the first logic board LED light up, and the ODD fan spins momentarily and that's it. I will get the three logic board lights until I plug in the display power cable. If I leave off the display power cable, but all the other LCD cables are plugged in, I will get 3 logic board lights. The screen was fine before I took it off, so I am not sure what I did to keep it from working. I checked the continuity in the display power cable and display data cable, and they appeared to be okay. Any ideas besides a new screen?
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iMac 27" 2011 Won't Boot with LCD After GPU/CPU Upgrade
- Thread starter jimmi56
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How about swapping the LCD panel between 2 iMac to verify that they are both fine?
And to verify that the K4100m is working or not, you can try another MXM card on that iMac, also.
I finally got around to do some more troubleshooting:
Both LCD panels are fine.
I swapped in a hard drive with Sierra and it booted with picture. I did a clean install of Big Sur using opencore. Turns out, the logic board I recently purchased off eBay still had remote management enabled so that did not allow me to log in. I then swapped in the other hard drive to see if it would now work. It did not, but now it won’t boot even when placing the hard drive that was working back in. I also swapped mother boards to another working one, and it still won’t boot.