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Gap between the center of CPU and lapped heatsink

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March 29, 2010 4:10:42 AM

I applied AS5 to an A64 X2 3800 CPU and spread it into a thin layer and then put a lapped heatsink that came with the CPU onto it and it was running for a few weeks.

Today, I decided to try a different thermal paste and when I removed the heatsink, I saw that the center of the CPU was not making contact at all with the heatsink. Only the edges of the CPU made a mark on the heatsink.

Could this have done any damage to the CPU or shortened its life? When I ran prime95 during this time, HWMonitor reported a max temperature of 47C and idle temperatures in the low 30s which I thought was normal. Could this have been inaccurate since the center of the CPU was making 0 contact?
March 29, 2010 4:29:56 AM

since your temps were fine, there will have been no damage to the CPU. The heatsink should be lapped again to achieve a truly flat base, making more contact with the actual CPU. This will also in turn reduce the temps a little farther.

47 for full load with Prime95 isnt that bad, actually.
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a b K Overclocking
March 29, 2010 4:42:35 AM

I agree. I think it was making contact with the center of thr cpu. You wouldnt have had those temps if it wasnt touchin it.

A good way to check is to put some thermal paste on a clear piece of glass or plastic then put the heatsink on the plastic and push down at the edges of the cooler with a lot of pressure. Look umderneath the glass now and see if it making contact.
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a b K Overclocking
March 29, 2010 6:04:41 AM

Overshocked - Excellent recommendation about using glass! ^5

There is another possibility. You're cpu may not be flat. Check your cpu with the edge of a credit card or something thin to see if it is flat. Normally cpu's are not flat. When lapping it is customary to lap the heatsink and the cpu.
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a b K Overclocking
March 29, 2010 6:06:20 PM

Thx, i actually got it from conumdrum though XD.

Anyway, johnny is right, the cpu's usually have higher edges than the centers.
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a c 86 K Overclocking
March 29, 2010 6:26:21 PM

Umm I said use kechtup as the layer. Some thermal pastes (like MX3) are so thick I don't think you can hand pressure enough.

Anyhoo. Pacing the CPU on glass and looking up through it or a long razor blade across the top of the CPU with a flashlight shining through the crack tells you a lot.

If it's your first CPU your checking, it doesn't tell you much at all tho, it's learned by experiance whats bad/good.
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a b K Overclocking
March 29, 2010 6:38:39 PM

^ Srry conundrum, could have sworn you said TIM.
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a c 86 K Overclocking
March 29, 2010 7:24:53 PM

No worries, you are no noob and no apolgies needed. Your one good informed dude.
!