recently i changed the 6 month old motherboard for my PC with a new one.. and i'm facing problems with the CPU fan because electric noise passes from the motherboard to the fan and it's very loud!!! with the previous motherboard everything were fine.
i can't stand it because every time i'm running a program or move the mouse the noise changes! if i disconnect the fun goes away.
the fan works just fine without noises with an external psu...i also tried few capacitors i had in front of me and still nothing the noise remains... (1uF, 47uF, 100nF,270pF)
You could buy a fanless powersupply if the noise bothers you. Or a large fan type supply they tend to run slower.
Of course you could try the PWM mod in the app note.
do you think it worths spending time on it? as i said i already tried
few capacitors from +12V to GND and did nothing! but that was before i discover the pdf link i gave you!
Yes, you need a capacitor but also a series resistor.
The cap goes in parallel to the fan, and the resistor goes in series
with the capacitor from the PWM control signal.
You might try different value resistors like 1k, 2k, 5k, etc.,
and 1uf, 10uf caps.
The idea is to stop the pulsing from getting to the fan motor and
supply it with a smoother voltage instead. The resistor and cap
do this, but the cap alone wont work as well.
and also it's not a solution to disable the PWM control wire so i can
totaly stop the electrical noise.
[edit]
@MrAl do you think it will work? not all motherboard have the same fan control IC.
the PDF link i gave is a random one i got while i was searching the net.