[mythtv-users] Fancontrol with replaced CPU fan

[Johnny]

> I always thought if you plugged a 3 pin fan in these 4 pin pwm headers
> you would get no voltage control and the fan would run at full power
> always.

I think you are right. On the 4-pin headers the PWM is on the 4th pin.
So when you plug in a 3-pin fan you only get the standard power with
no PWM. But on both of my Asus motherboards they have a feature they
call Q-fan that lets the bios regulate the 3-pin chassis fans as well.
According to fancontrol and pwmconfig these 3-pin headers are able to
use PWM. I have another 3-pin header for the power supply fan that
doesn't have any PWM control (or Q-fan). So they must do something on
the motherboard to allow for the PWM control on some of the the 3-pin
headers, and it is different than whatever they do with the 4-pin
headers. They are specifically designed so that you can put a 4-pin
fan on a 3-pin header and a 3-pin fan on a 4-pin header, and they will
work at full speed, but you won't have PWM control in either case.