Older computer with asus mobo and amd chipset.  The fan on the  northbridge is out and I can't find a replacement.  I removed the fan and the housing that holds the fan is still attached over the CHIP by two spring-loaded attachments at diagonal corners----it appears I'll need to remove the mobo to remove the fan housing from behind.  The fan size is 40mm square.  I can purchase heat sinks that are 37mm.

Q: Are the two attachment holes on the mobo standard.  In other words, if I purchase a northbridge heatsink, will it fit?I can't think of a processor fan that would be mounted on the underside of the motherboard.  However, I have seen some fairly ludicrous methods for mounting a CPU Fan/Heatsink combo.  Look at the pins that hold the fans frame down.  There may be some difficult-to-see instructions on them, i.e. Arrows that indicate a necessary turning or perhaps lift pin that's just VERY snug and may take an ounce of gutsy muscle to disengage it.

I have one that requires you to turn the thumb piece to the left to unlock the lift pin, then you have to squeeze the thumb piece and the lift pin together with all the strength in your index finger you can find and that corner pops off the mobo all its own.  All my smarts and took me a half hour to figure that out.  Not to mention it was Best Guess which WAY I turned the thumb piece for lock and unlock.

As for where to buy.  Try newegg.com  Their Advanced SEARCH function allows you to filter down to exactly what you need.

Good Luck!It's a strange setup.  The fan housing has spring-loaded pins attached to the mobo somehow ... no instructions or obvious ways to remove it.  I've decided to take it apart because I need the experience.  Maybe I'll just put a whole new fan assembly on.  I wonder if it's necessary to put thermal grease between the chip and metal fan housing?

Thanks Lyniaer.If you take the OLD one to a PC store they should be able to match it up for you...

Thermal paste is recommended.More like necessary.

Just put on no more than a dime-sized dallop.  Too much and you'll isolate the heat onto the processor instead of transferring it to the heatsink.