Help me figure out this BIOS Error

July 6, 2006 6:49 PM

I'm experiencing the following BIOS error: "CPU Fan Error!" Please help me figure out how to solve the problem.

I'm building my friend a computer and after turning it on the first time I recieved an error: "CPU Fan Error!" It's an Asus A8N32-SLI Deluxe Motherboard with an AMD Athlon 64 X2 proccessor. The fan I have attached is a Thermaltake Silent 939 K8 fan. There is no operating system installed yet, I just turned the thing on and I'd like to not destroy a fairly expensive processor.

I've built a few computers before this one and it looks like the fan is on right to me, it's running smoothly and quietly and the temperture of the processor is hanging around 40' C. It feels secure and I put on thermal paste as well. So I'm kinda baffled as to why it's presenting me with this error. I'm hesitant to proceed because it's not for me specifically and I don't like risking other peoples money on things. Don't bother telling me to RTFM, I've been through it three times now and there is nothing even resembling a help section in it, nor does the section on the BIOS offer anything usefull. Even at the BIOS's web site's (www.ami.com) their documentation has no mention of this specific error, or even anything close. Will this error go away when I install XP? Am I being over cautious? Thanks in advance.

posted by SteveFlamingo to computers & internet (5 answers total)

If the error is truly based on the fan and it's not some random incorrect message, there is basically one source, which is the fan's tachometer. (I don't know if that word really applies here, but it measures the RPM.) Technically you could diagnose a fan error by the current consumption of the fan, the lack of cooling on the temperature sensor, or some other weird way, but I really doubt they would bother implementing anything but the tachometer measurement.

Your fan should have three wires coming out of it: + (should be red), GND (should be black) and the tachometer signal. If I remember right the signal wire is in the middle. All this wire does is pulse as the fan rotates, and the motherboard counts the pulses and determines RPM.

So check that your fan does indeed have the three wires. Also check that the connector is plugged into the CPU fan header as opposed to one that's called "System fan" or "Case fan" or something, as it will expect the signal pulses on that header. If the screen where you see the CPU temperature shows fan RPM, check to see that you are getting an RPM reading from the CPU fan.

If you've ended up with a fan with no tachometer, or a broken tachometer, it's nothing big to worry about. If the fan really broke, the system would become unstable but shouldn't just die.
posted by TheOnlyCoolTim at 7:10 PM on July 6, 2006

You have the Southbridge fan plugged in, right?
posted by Civil_Disobedient at 7:20 PM on July 6, 2006

If you look in the BIOS, it might tell you right there if you have it plugged in wrong. Assuming you have no other fans plugged in, if one of the case or power supply fan entries has a tach reading, that means you plugged it into the wrong place.

It's generally best to get the CPU fan into the right socket... the BIOS will speed up and slow down the fan as necessary for the current CPU temp.

If you really don't want to bother, you can usually disable any given monitor, but the fan protecting your CPU is not, IMO, one you want to ignore. You need to know if it's spinning too slowly to do its job. That will usually give you some warning before outright failure.
posted by Malor at 7:21 PM on July 6, 2006

Thanks TheOnlyCoolTim, you nailed it with the connector being plugged into the wrong connector. Thanks also for the detailed explanation of the third cable on the chord, now I'll sound even nerdier when I build a computer with my next friend.

Not even twenty minutes and I have the problem fixed. I sure do love Ask MetaFilter.
posted by SteveFlamingo at 7:23 PM on July 6, 2006

Malor, thanks for the heads up and this is exactly why I was kinda concerned about having the CPU Fan not being installed correctly.
posted by SteveFlamingo at 7:24 PM on July 6, 2006