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Heatsink/ Heat Pipe / ThermoSiphon Cooling The cat will only make the mistake of putting its paw by your HSF once. :) Also the place to discuss the new high end heat pipe goodness. |
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#1 |
Cooling Neophyte
Join Date: Jun 2005
Location: Dreamland
Posts: 37
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I got a PowerMac G5 dual 1.8 GHz PowerPC machine at a great price, so I thought I might play around with it a bit (I'm a PC guy). After acquiring the machine I read a large number of online complaints about these units failing due to 'thermal runaway.' It seems that Apple and IBM had some issues with these, to put it mildly.
I decided to investigate. I loaded a program called Temperature Monitor and observed the idling temps, about 41 degrees C on each CPU die. Then I loaded and ran a program called CPUTest to stress the CPUs and observe the temps. Both die temps, over about 4-5 minutes rose to about 58 degrees C. Next I pulled the CPU/heatsink modules out and examined them. The CPUs are mounted to small PC Boards with some support components, and strapped to the bottom of this huge passive heatsink. I pulled one assembly apart, cleaned off the existing thermal paste, carefully applied a 'silver' heatsink paste, reassembled the CPU and the machine. Now when I test, both CPUs seem to idle at about the same temperature, 41 degrees C. When I start CPU test, however, the modified CPU jumps 10 degrees C to around 52 degrees C almost instantly, then rises to 58 or so and stays there. The other, unmodified CPU will start climbing slowly over 4-5 minutes to about the same temperature. Apple wants their service dealers to run a thermal calibration program on the machine when CPUs are changed or problems arise, and I have done so. I know that the silver paste will take some time to 'settle in', up to around 200 hours accorcding to one online report I'd read. What I'm wondering is whether or not this fast temperature rise behavior is "normal." Any input appreciated... |
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#2 |
Cooling Savant
Join Date: Jun 2005
Location: Skokie, Illinois
Posts: 322
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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.
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My new rig.... Intel SE440BX-3, PIII 550 (@ 680) MX440 275/332 (@ 350/400) and 3DFX Voodo 5 5500 160/160 (@180/180) Two Opticals and 120 gigs (w/28gigs in RAID0) on 4 Maxstors |
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#3 | |
Cooling Neophyte
Join Date: Jun 2005
Location: Dreamland
Posts: 37
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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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#4 |
Uber Pro/Mods
Join Date: Aug 2007
Location: New Hampshire (USA) Posts: Two hundred somethin
Posts: 432
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Think you could take a few pictures? All you really need is a good mount and just a small amount of thermal paste but it would be interesting to see your CPU/HS setup.
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#5 | |
Cooling Savant
Join Date: Jun 2005
Location: Skokie, Illinois
Posts: 322
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AS5 instructions Yes, pics.
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My new rig.... Intel SE440BX-3, PIII 550 (@ 680) MX440 275/332 (@ 350/400) and 3DFX Voodo 5 5500 160/160 (@180/180) Two Opticals and 120 gigs (w/28gigs in RAID0) on 4 Maxstors |
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