ASRock Z87E-ITX CHA_FAN1 PWM Oddity

[Quad5Ny]

I picked up some Noctua industrialPPC PWM fans that should be able to run at <400RPM but they refused to run unless the duty cycle is above 37% (800RPM). After checking with my multimeter the board is using DC control and the 12V line is @ 5.3V and the Control pin (Pin4, PWM Signal) is at 1.34V.

Now the above is annoying not unusual (MB manufacturers lie) but why isn't Pin4 be a steady +5V if the board is using a fake PWM header?

 

[phasseshifter]

put an oscilloscope on it and look at the wave form..also u did not mention what brand of mobo u are using...check your bios settings..it may well be that your computer power supply is at fault...perhaps some more info posted may help things..you may have a crook regulator on the mobo...

 

[ctbaars]

^ Yeah. I bet there is a 44/56 square wave in there.