cpu fan never spins

Posted on 2005-04-22
Last Modified: 2010-04-26
i recently put a amd duron to replace an athlon which didn't seem to be working .. but I noticed that with the original athlon the fan never seemed to kick in .. and now with the "new" duron also with a new fan the same thing seems to be happening .. is there a way to check that it's working ok?
Question by:stefanomarco
    LVL 69

    Expert Comment

    The fans are powered by 12v, so use a multimeter to check if the motherboard header is providing voltage.  You can plug the fan in another header, but most AMD motherboards expect to sense a cpu fan spinning, or they will shutdown.
    LVL 10

    Expert Comment

    pretty sure if he had a multimeter and knew how to use it he would probably not be asking here but it is a good way to test if you have one

    Author Comment

    i don't have a multimeter ... I've been doing a virus scan now for about an hour where the cpu usage spiked a few times to around 100% but not once has the fan come on .. unusual?

    Author Comment

    maybe this is why the original one died?
    LVL 3

    Accepted Solution

    As others have hinted,  most AMD mother boards use a tachometer sensor  to detect whether or not the CPU fan is spinning and will prevent the machine from operating if no fan rotation is sensed.  This is why most fans have three wires instead of only two.  The third wire is for the tach sensor. This feature has saved many cpus from frying themselves.

    Having said that, your problem is unique in that the machine will boot up but, as you state, the fan is not spinning.  This will most likely result in an early demise to your CPU.   I've built several Duron 1.6 machines and even though I have tried, I have not yet been able to run one "fanless" without overheating the CPU.

    Things to look into:

    Make certain the fan is connected to the proper place.  Most Motherboards have several identical looking connectors labelled things like "CPUfan",  "Sysfan" etc.  Make certain that the CPU fan is attached to the MB connector labelled for that purpose.  You may have to consult the MB documentation to be sure which connector is correct.

    If that fails,  the next best thing to do would be  connect the fan directly to the power supply. Unless your machine is fully loaded you probably will find a spare connector or two hanging off the supply.  These conectors will most likely be of the variety called "molex connector".   In this configuration, the fan will run full speed all the time.  If the noise is too much for you, go get a new fan that includes a speed control.  I like the Vantec Fanmates.  In my experience, an AMD duron 1.6 can be run with a single fan at around 2000 RPM. The result is a nearly silent machine.


    LVL 69

    Expert Comment

    You could have a bad motherboard fan circuit or a dead fan, but the fan should always be on and running.  You can also plug it into another system and see if it spins, but only do it very briefly - the other system needs its cpu fan to do its job, too.

    Author Comment

    thanks all :)

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