Subject: BTX Case Fan
By: Brett (IP: 65.95.133.*)
Written on: 15-07-2006 13:39
I installed an Intel BTX mobo with some Cooler Master Ultra SIlent case fans. The mobo docs state that "The features of the hardware monitoring and fan control ASIC include...Thermally monitored closed-loop fan control, for all three fans [note: they mean the CPU fan and front and rear case fans] that can adjust the fan speed or swith the fans on or off as needed" (Intel D915GMH Technical Product Specification).
So the CPU fan has a 4-pin plug and works as advertised at variable speeds.
However, the mobo 3-pin plugs for the two case fans are problematic. They either work full speed all the time (by disabling case fan logic in BIOS), or (apparently) not at all (if case fan logic is enabled in BIOS).
Is there actually a standard for variable-speed 3-pin case fans? I'm thinking that I've installed single-speed case fans which explains why they don't run at high speed when the system is hot, and throttle back to low speed when the system is cool (BIOS setting). But how would you run a 12V case fan at multiple speeds with three pins? PWM?