iMac 27"(Late 2013) A1419 problem (GPU?)
I have a possible GPU issue with my 27" Late 2013 Core i7 iMac, but not 100% sure (maybe 95%). The GPU is NVIDIA 775M.
First some background - the iMac worked fine from 2013 to I think 2021. Then the SSD simply disappeared and Apple Hardware Test also said VDH002 issue with storage device. I was not in the mood to open the iMac and swap the SSD then, so I simply reinstalled on external SSD and it worked like a charm for a year or so.
Then some random crashes and reboots started happening, mostly when using Google Chrome / Firefox with lots of tabs. This then progressed to what seemed like apparent GPU problems with parts of screen freezing, sometimes the iMac just did a sort of "soft" reboot - seemed to hang but then login screen appeared really fast but all apps needed to be reopened (automatically). In the end, there were colorful squares on the screen etc and sometimes it booted sometimes not. Around that time I also tried CInebench R15 and some other GPU tests and as soon the test started the system crashed.
Last week I opened the iMac, cleaned it, installed new OWC blade SSD, repasted the CPU and GPU and added thermal pads for VRAM (1mm thick, perhaps not enough?). I managed to install the OS (Catalina) without issues, did CPU stress test (4771 i7 goes to 95C and then fans keep it there 10 minutes on 100% load). But, as soon as I tried Cinebench R15 or other test that uses OpenGL it crashed again. I even installed WIndows 10 to try 3D Mark and try to see it there is some kind of driver problem with Mac OS, but no, also hangs in Windows 10. Strangely, when running the Heaven Ungine on lowest setting it crashes the software but OS then recovers, image of the test stays on parts of the screen but when I draw a rectangle around them the desktop image comes back.
I tried running Apple Hardware Test again after these fixes but it still says just VDH002 issue with storage device, but the SSD works fine...
Temperature wise, the GPU seems to crash instantly, not related to temperature. I cannot even get to GPU temps more than 53C.
Any ideas? Try repasting GPU and VRAM again but with K5-PRO (I used Arctic Silver 5 for GPU and CPU and Arctic pads 1mm for VRAM).
UPDATE: Photo of temperatures and other data from HWINFO64.
Questa è una buona domanda?