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MA78LM-S2H Northbridge Heatsink issues

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August 4, 2010 5:33:13 AM

Basically the thing was loose when I got it (It would wobble on the two unsecured edges), so when it was clear that it was going to be running too hot, I took it off and the dry thermal paste/pad thing had come apart. I took some alcohol and cleaned it all off, put some Ceramique on it, and tied it down with 2 nylon screws in place of the springs and plastic pins.

Still, I get an idle temperature of about 75C.

Over 100C with load (~15 seconds into Prime95)

The heatsink is hardly warm...

I get the feeling that the heatsink isn't making contact with the chip. There's a foam rectangular outline attached to the heatsink that goes around the chip, and i think it might be keeping the aluminum from making contact. I don't know if its necessary. I really have no idea what to do.

Any and all help is much appreciated!

System:
Athlon X3 3.0Ghz
4GB OCZ Platinum DDR2
ATI 4850 1GB at 700Mhz

a c 177 V Motherboard
August 4, 2010 1:30:19 PM

I think you're right - the 'foam thing' is likely your culprit. I don't 'do' AMDs so I have no direct experince with them, but: typically, the 'aux sinks' (the bridges and MOSFETs) are put on with a heat-conductive transfer pad, and spring-loaded snap-pins. One of the functions of the pads is to accommodate the heat-pipe sink assembly being a tiny bit out of alignment - hard to make something like that 'dead' flat, consistently...

What I do with my own boards is pretty similar to what you've done; I use #4-40 nylon screws, with the original springs for tensioning, and 'paste 'em', as you cannot just re-use the snap pins - the 'stack height' is different without the thermal pads. In your case, what I think is happening is that the thermal pad thickness got it 'up inside' the foam surround - now that the pads are gone, you're getting a gap... I would have no hesitation at all in removing it, and would suggest carefull work with an Xacto knife with a flat blade - one whose 'edge' is at 90° to the handle - can pick 'em up at any hobby shop...
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August 4, 2010 2:37:50 PM

Should I be worried about shorting exposed components on the northbridge? Is there anything I can use to replace the foam... maybe a thinner foam that can hold up to temps or a tape?
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a b V Motherboard
August 4, 2010 2:42:42 PM

Hi g33j,

I think you are right on about the heat sink not making intimate contact with the CPU. I downloaded the manual, and it looks like installing the CPU and heat sink is straigforward.

I would clean the CPU and Heatsink surface with 99% isopropyl alcohol or the Arctic Cooling 2 part cleaning solution. If there is a ridge on your heatsink that prevents direct contact with the fairly large CPU top, that should be carefully corrected.

It's not just the outside of a heat self adhesive pad that may have been used, which pulled apart, and not completely removed?
Once you can get "direct contact" with the two metal surfaces, then use a small amount of heat sink paste and smooth it out in a very thin coat with the edge of a credit card. The paste is to fill in the irregularities in the two surfaces, not as a cushion or thick interface to correct for improper screw mounting.

The other thing to consider is to purchase a new headsink that is compatable with your MB. They cost $25 - $50 for higher end ones, and it is much less expensive than having your AMD CPU burn up and have to replace both components.
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