On 06/12/11 00:35, Phil Pokorny wrote: > Some motherboards have BIOS settings to switch between PWM control and > voltage/3-wire control. (I saw this in an ASUS BIOS for the CPU fan > header). But your essential point is correct, that a header > configured to use PWM to control fan speed will not work with a 3-pin > fan. > On more than one ASUS motherboard, I have encountered 4-pin headers > that *do not drive* the PWM pin and instead do voltage control of the > fan speed. This is most common on the chassis fan headers. They are > 4-pin headers, but they don't have an active PWM signal and you can't > enable it in the BIOS. I asked ASUS about it and they said it wasn't > possible to generate PWM signals on those headers. > > When you plug a 4-pin, PWM controlled fan into such a header, the PWM > signal is floating and so the PWM fan will run at "full speed", but > the variable voltage will result in the fan speed changing under the > control of the motherboard. Thanks for the explanation Phil The ASUS P8H67-V behaves that way with CPU_FAN working as a "proper" 4 pin header and CHA_FAN1 and CHA_FAN2 behaving as 4 pin headers with a floating PWM signal. _______________________________________________ lm-sensors mailing list lm-sensors@xxxxxxxxxxxxxx http://lists.lm-sensors.org/mailman/listinfo/lm-sensors
