Paul wrote:
> I don't know anything about the Intel motherboards, but I can pass on
> some generic info.
>
> There are a couple ways the CPU fan speed can be controlled.
>
> 1) Intel in the past, has made the boxed heatsink/fan sensitive to the
> air temperature inside the computer case. The Intel fan has a
> thermistor mounted in the fan hub, and the thermistor controls the
> fan speed. As the computer case air gets warmer, the fan will spin
> faster. The Intel datasheet for your processor, will state the
> two temperature points used to "ramp" the fan speed. But according
> to Intel, the fan should spin at all times.
>
> 2) Motherboards can also have voltage control of the CPU fan header.
> The motherboard can monitor the CPU temperature, and adjust the
> voltage to the CPU fan header, to trade off CPU temperature for
> fan noise. The BIOS may offer some setting which switches on
> this voltage reduction feature (like your Smart CPU Fan mode).
>
> It is possible if both techniques are combined, to have a fan
> spinning at zero RPMs (that is because using both techniques at the
> same time, means the fan runs even slower than with either technique
> by itself). But, since the average BIOS is designed to
> detect a zero RPM spin state, as a fan failure, it takes careful
> coordination of the BIOS design, if the design intent was really
> to allow for the fan to stop. I'd say they probably did not intend
> for the fan to stop, if the BIOS is flagging the failure.
>
> To avoid any voltage control issues from the motherboard, you
> may be able to find a power adapter that goes from a Molex disk
> drive power connector, to a three pin fan header. Note that your
> Intel fan has a four pin connector, and one pin will "hang over"
> if used with the adapter. The fourth pin does not need to be driven,
> and a four pin Intel fan can run from a three pin header. Running with
> the adapter, ensures the fan is getting the full +12V.
>
> If the fan continues to start at zero RPM, when the system starts,
> then I would conclude the fan was defective. It could be that
> the thermistor inside the fan hub, is "overdoing it" when adjusting
> the fan speed.
>
> So, it could be that the Intel fan itself is not working properly.
> Or, it could be the combination of Intel fan plus motherboard
> Smart Fan feature. Running the fan from an adapter may help distinguish
> between the two states, and whether the fan is working properly.
>
> Paul

I tried the power adapter today and the fan started spinning the moment
I hit the power button. So I'm guessing it's some new technique that
allows the fan not to spin at all if CPU temp is too low, thus saving
some power.
Thank you for your advice. Now I know I have a perfectly working CPU
fan.

Ovidiu