Go Back   Pro/Forums > ProCooling Technical Discussions > Heatsink/ Heat Pipe / ThermoSiphon Cooling
Password
Register FAQ Members List Calendar JavaChat Mark Forums Read

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.

Reply
Thread Tools
Unread 03-15-2009, 01:14 PM   #1
Harbinger
Cooling Neophyte
 
Join Date: Jun 2005
Location: Dreamland
Posts: 37
Default Mac G5 Heatsink Upgrade Question

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...
Harbinger is offline   Reply With Quote
Unread 03-15-2009, 09:54 PM   #2
billbartuska
Cooling Savant
 
Join Date: Jun 2005
Location: Skokie, Illinois
Posts: 322
Default Re: Mac G5 Heatsink Upgrade Question

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.
__________________
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
billbartuska is offline   Reply With Quote
Unread 03-17-2009, 09:07 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.
Harbinger is offline   Reply With Quote
Unread 03-17-2009, 09:12 PM   #4
ben333
Uber Pro/Mods
 
ben333's Avatar
 
Join Date: Aug 2007
Location: New Hampshire (USA) Posts: Two hundred somethin
Posts: 420
Default Re: Mac G5 Heatsink Upgrade Question

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.
__________________
Pro Slacker
ben333 is offline   Reply With Quote
Unread 03-18-2009, 09:17 PM   #5
billbartuska
Cooling Savant
 
Join Date: Jun 2005
Location: Skokie, Illinois
Posts: 322
Default Re: Mac G5 Heatsink Upgrade Question

Quote:
Originally Posted by Harbinger View Post
...which, oddly enough, isn't silver
... used a razor blade to carefully spread a thin layer of the AC5 onto the CPU.
AS5, like most TIM, is a suspension of tiny silver particles in some "goo" that squeezes out and leaves mostly just the silver particles between the HS/block and CPU.

AS5 instructions

Yes, pics.
__________________
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
billbartuska is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -5. The time now is 12:29 AM.


Powered by vBulletin® Version 3.7.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
(C) 2005 ProCooling.com
If we in some way offend you, insult you or your people, screw your mom, beat up your dad, or poop on your porch... we're sorry... we were probably really drunk...
Oh and dont steal our content bitches! Don't give us a reason to pee in your open car window this summer...