2011 iMac GPU / Logic board issue issue

[andrew.gasiorowski]

I have recently got hold of a 2011 27" iMac that had a faulty GPU (6790m). After a temporary baking it revived the board and I managed to get the system up and running from a time machine backup.

All of the sudden the Mac reboots and now does not post (no chime) and has a black screen. There are only the first 2 diagnostic lights lit on the logic board.

Powering on the machine will power up the fans and HDD with the CPU fan running full speed after about 10 seconds. Swapping the GPU for a known working card from my 21.5 iMac from the same year also results in the same response.

With ram removed get the expected result of one long beep. Nvram and PRam reset does nothing.

Any ideas as I am all out of them just now?

 

[b06tmm]

When I baked my mid-2011 video card I damaged the LVDS cable for the screen and had exactly what you describe, black screen and fans on full blast.

I purchased this as a replacement: https://www.amazon.com/gp/product/B01B5VG4AM/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1, and being very careful installing the new cable was able to get my system running again.

 

[andrew.gasiorowski]

When I baked my mid-2011 video card I damaged the LVDS cable for the screen and had exactly what you describe, black screen and fans on full blast.

I purchased this as a replacement: https://www.amazon.com/gp/product/B01B5VG4AM/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1, and being very careful installing the new cable was able to get my system running again.

Thanks for the reply, I don't think it's the cable as the machine is still not passing post (chiming at boot) with the screen removed and with or without a known working GPU fitted. I may as well give it a go but I have a refurbished logic board coming so will be interesting to see if the same behaviour occurs with that.

 

[andrew.gasiorowski]

Just to follow up. After changing the logic board the machine booted fine and seems to have fixed the problem.