Possible iMac G3 Dead CPU from Overheating

[benwlloyd]

Hi all,

I have a 1999 Lime Trayloading iMac G3. I bought it without a HHD, so I took it apart to install it and check the condition. I noticed that there was no thermal paste / thermal pad between the CPU and the heatsink, but for whatever reason I didn't think anything of this as there was no residue. It was used relatively intensely through repeated OS X installations. When it was finally all working, it just died.
When you press the power button there's some CRT degaussing noise, and the power button turns orange, but there's no chime. I have tried a PMU reset, replacing the RAM, and reseating all the internal parts accessible on the Logic Board.

It only just occurred to me what I may have done - have I killed the CPU through overheating it? If this is the case, is there anything that can be done short of buying a new Logic Board?

Thanks for your help.

 

[pete1]

The stock heatsink usually has a black thermal pad adhered to it, so perhaps this had been scraped off?

Assuming you had the heatsink and spring clip correctly installed (even without the pad), and the chassis fan is working, then I’d say the CPU is probably fine and that the issue is elsewhere. True, thermal transfer would be poor, but not non-existent. if it was heat related you’d probably have seen instability and lockups some time before the chip failed. In other words, warning signs.

Also it sounds like you’ve only recently acquired the iMac and that it had run in this configuration - without a thermal pad - in the past, without issue.

If you’re not sure, acquiring a spare CPU daughtercard (not logic board!) would be the sensible thing to do, and you could either confirm or rule out damage to the CPU. They’re not especially hard to come by, or especially rare. I trust you have already tried reseating it?