My MOBO is Asus P7P55D-E PRo. Currently I have 2 scythe gentle typhoons on a megahalem cooling my cpu. They are both 3 pin fans. I have one hooked up to CPU_fan header and another to Chassis_fan header. They are running at full speed which I didn't mind as I was testing OC and max loading anyways.
In any event, I'm done OC and want to be able to start having the fans run quieter at idle but am having problems. I've tried both BIOS control and Asus Fan Xpert and they are both able to slow down the fan on the Chassis_fan header but not the CPU_fan header.
My guess is that the CPU_Fan header is trying to control it with PWM as it is a 4 pin fan header. Is there any way around this? Is the CPU_Fan header only capable of PWM control and not able to just drop voltage like I believe the chassis_fan header is doing?
Seems you already figured it out. You'll need a 4-pin fan on the CPU fan header in order to have fan control. One option would be to run a "Y" adapter cable off the CHA_FAN header. You'll have to go into the bios/Power and set "CPU Fan Speed" to "Ignored" or it will keep bugging you about no CPU fan detected.
None that I can think of personally, this comes up quite often in regard to Scythe fans/CPU coolers. Contact the manufacture and ask them, it would interesting to know why they (and others) sell 3-pin fan/CPU coolers when they know it don't support fan control on the CPU fan header.