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Unread 03-17-2009, 08:07 PM   #3
Harbinger
Cooling Neophyte
 
Join Date: Jun 2005
Location: Dreamland
Posts: 37
Default Re: Mac G5 Heatsink Upgrade Question

Quote:
Originally Posted by billbartuska View Post
Generally, a fast CPU temperature rise indicates a ineffective heat transfer between the CPU and it's heat sink.
Just a guess, but the new thermal compound may not be making complete contact between the CPU/Heat sink (thus the fast temp rise) but be more effective at transferring the heat (and thus able to maintain the same maximum temp with less contact area). I'd check the CPU and heat sink for flatness.
Thanks for the pointer! I went out tonight and got a tube of real 'Arctic Silver 5' (which, oddly enough, isn't silver like the knockoff compund I was using but rather a gray color). I tore the assembly down again, cleaned off the silver paste, then used a razor blade to carefully spread a thin layer of the AC5 onto the CPU. I then reattached the board as recommended (with one screw on each corner of the CPU, a turn at a time, opposing corners) so all was tight again.

Now my temp on that CPU is only 5 degrees C higher under moderate load than the unmodified CPU, not 15 or so. They're both extremely close at idle.

I don't think I can get any tighter/closer match or bond between the CPU and the 'sink. I'm going to put the machine through heating/cooling cycles and give the paste a chance to settle in now. I'll let you know what happens.
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