CPU fan enigma

[maudman]

CPU (AMD 3000+ XP) temp at idle was about 52C and 61C gaming. Ordered fans and heatsinks and they would not run with the Asus mobo. Run for a second and shutdown. I figured that since the electronics were in the fan I might get a little more cooling from the copper heatsink and the old fan. Wouldn't boot. Huh? Put 7000 RPM fan on old heatsink and it booted right up! Idle at 43C now. Go figure.
What the heck did that mobo like so much about the old heatsink? You'd think that the signal from the fan was shutting it down.

Maudman

 

[paparazi]

Practically all motherboards are fitted with a fan speed sensor, this is just for protection in case of fan failure.
Trouble is if the motherboard doesn't like the signal given out by the fan (it is too slow or a poor signal) it will shut down after 1-2 seconds.
The heatsink was certainly not the problem, it was the fan, for some reason your motherboard is having problems detecting a RPM signal from it so shuts down.
The fan could just be faulty but I have seen this problem many times with dual fan setups and low speed 70/80mm units.
Martin

Replying helps further our knowledge, without comment leaves us wondering.

 

[dakota81]

Could also be improper installation of the heatsink. Once I accidently clipped the heatsink on backwards, such that it never made contact with the cpu. The motherboard detected the rapid rise in cpu temperature and shut itself off immediately.

 

[paparazi]

dakota81 has a good point,
It is very easy to clip the heatsink the wrong way around and not realize that the heatsink is not sitting squarely on the CPU core (nearly all socket A heatsinks have a recess in the base so as not to foul the "cam box" side of the CPU zif socket.
Modern motherboards that have core temperature sensing will detect the almost instantanious overheating and shut the computer down.
So recess in the heatsink base needs to be positioned over the socket "A" writing of the CPU socket.
Martin

Replying helps further our knowledge, without comment leaves us wondering.

 

[maudman]

I didn't know that you could put a heatsink on backwords. There were no recess' on any of the heatsinks. As for the fan portion, the mobo ended up liking the new fan and disliking the old fan. No copper heatsink ever worked on this board. Just aluminum. BTW, while looking at my old heatsink I saw dust between the fins and blew it out. Just something else to check when doing maintenance. No evidence of it by just glimpsing but hold it up to the light and you'll see it. Maybe I should have known that.

Maudman

 

[paparazi]

On these copper bottomed heatsinks the "recess" as I discribe it is the ofset billet of copper.
Ofset so it doesn't catch on the crank box (thats the lever mechanism that holds the CPU in place) if you look closely you will notice one side of the Zif socket (CPU socket) is raised and that is why the heatsink base has eith a recess in it or the billet of copper is ofset and doesn't go all the way across the base of the heatsink.
I don't think I can explain it any more simply but to assure you it is a very important point, get the heatsink on the wrong way around and the CPU will overheat usually fatally, simple as that! so look again it is important.
BTW copper has nothing to do with it, the fact that your motherboard seems not to like copper heatsinks is purely coincidence and very probably down to fitting the heatsink the wrong way around, especially considering you admit you never knew there was a wrong way.
Don't forget heatsink paste on the raised CPU core.
Martin

Replying helps further our knowledge, without comment leaves us wondering.

 

[maudman]

Well, that makes sense but I just looked at the heatsinks and front and back would be VERY vague.

 

[Jontmke]

I agree with paparazi, the bios does not sense any rpm from your fan and shuts down. What you could do is go into the bios with the working fan and turn off the safety feature that tells it to shutdown if it does not find a fan. Then put your new fan on. But you would need to leave the tempurature setting on so that it shuts down if the cpu gets hot. An Athlon will fry in a minute or two with no fan.

Jon

There is much pleasure to be gained from useless knowledge. (Bertrand Russell)

 

[maudman]

I don't see that option in the BIOS but the 7000 RPM is working on the old heatsink and idling temp is now about 46C. Gaming temp is now 51C which is what I used to idle at. The old fan used to max out at 3500 and just wasn't enough. I may experiment with the 2 copper heatsinks later.

Maudman