Graphic card overheating, CPU fan in full speed, then black screen
I am a newbie to Mac and this forum, so please be gentle.
I recently acquired an early 2008 iMac A1225, EMC 2211 - 2.8GHz CPU, ATI Radeon 2600 pro graphic card, 320GB HDD, 24" 1920x1200 LCD.
It turns on with no problem. In around 10 minutes, the cpu fan runs in full speed (loud and noisy). GPU temperature reaches 128 Celsius degree in 10-12 minutes, and follows by black screen. CPU only gets 32 Celsius degree at the same time. As the computer is idle. Youtube video definitely speeds process, especially full hd videos.
Previously, Mac OS 10.8 installed. After reading some posts about similar issues, I tried to change it to 10.6, but got black screen after erasing the OS (no os now) during installation.
Things have tried:
- reapply GPU thermal paste using arctic silver 5
- kext tricks (10.6.2 as suggested by others)
- reset smc, pram
Update: I was able to reinstall 10.8 but not 10.6. Thermal paste seems to be working - heat sink reached 128 celsius degree while GPU die at 111 celsius degree. Previously it was reverse. However, the overheating problem is remained.
This iMac is virtually a stylish 20-minutes-iMac. It has a overheating graphic card and can not do anything.
I am answering my own question:
The only way to permanently fix the symptom is replacing the video card. I can confirm this because I just replaced my video card. I do not have GPU overheating issue any more. I have been watching full HD online movies for several days (stress test for the card), the overheating issue is gone. The highest GPU die temperature is 61C, normally it is around 50C without online videos. Before replacing the card, my old card can easily reach 128C in completely idle. I have been trying many ways to fix the old one, however none of them worked. Ways I have tried:
- replacing GPU heat sink compound
- adding an extra heat sink to GPU
- removing air wall under GPU
- reflowing GPU (the GPU died after this, don't try)