CPU PWM Function Not Working

meths · 13 Aug 2007 at 21:52

I want to turn my CPU fan down a bit using the PWM function but changing the value in the bios doesn't do anything although it works for my system and NB fans.

Using a DFI Infinity 975x/g and checked that the fan is compatible by swapping it with the NB fan to test.

Any ideas?

RJC · 13 Aug 2007 at 22:13

Got the same problem on my DFI board (same as yours), gave up and bought Zalman fan speed controler.

Rob

WJA96 · 14 Aug 2007 at 05:38

Is the fan definitely a 4-pin PWM one?

meths · 14 Aug 2007 at 08:29

Naw, it's three pin as I'm just plugging in a Vantec Stealth 80mm case fan as the CPU is watercooled.

I thought I might have to invest in a four pin fan.

RaiderX · 14 Aug 2007 at 10:08

Meths said:
Naw, it's three pin as I'm just plugging in a Vantec Stealth 80mm case fan as the CPU is watercooled.

I thought I might have to invest in a four pin fan.

you dont need the 4th pin if your manually setting the fan speeds as the 4th only is used for the Auto PWM fan control

meths · 14 Aug 2007 at 19:24

RaiderX said:
you dont need the 4th pin if your manually setting the fan speeds as the 4th only is used for the Auto PWM fan control

This makes sense as the fan works fine in the other 3 pin sockets.

Hmmmmn...WJA96 have you had a four pin fan working in this board?

EDIT:
Found this on the net in case anyone is interested...

The whole point of the four pin fan system is that it moves the PWM
switching transistor and associated components from the motherboard to the
fan itself. This allows the fan designer to tailor the switching circuit
design, pulse frequency and so-on to the specific fan model, rather than
rely on a generic "one size doesn't quite fit all" solution on the
motherboard.

Because of this transition, four pin headers, unless specifically designed
with a selectable option to control four *and* three wire fans, simply don't
have any voltage regulation hardware of their own. All they do is send the
full twelve volts up the power pin at all times, along with the low level
speed control signal up the fourth wire.

WJA96 · 14 Aug 2007 at 19:51

Meths said:
Hmmmmn...WJA96 have you had a four pin fan working in this board?

Yes, but obviously not your board