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PWM Fan Control on GA-P55A-UD6

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September 4, 2010 4:29:28 PM

I have my CPU fan (PWM) plugged into the CPU fan (PWM) header. I also have the rear case fan (another PWM fan) plugged into the SYS_FAN2 header. This is a 4 pin fan header and the manual shows the pin out that is close to the PWM cpu fan header but it shows the 4th pin as being reserved? How is my PWM fan going to behave while plugged into this header? Will it be controlled or just run at full speed? Please help.

Erik
a c 78 à CPUs
a c 235 V Motherboard
September 4, 2010 4:47:13 PM

Is you case fan 4-pin or 3-pin?

If it is a 4-pin, it can be controlled. If it is a 3-pin, it will run a full speed, as it doesn't have speed control.
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a b V Motherboard
September 4, 2010 11:33:32 PM

I have my CPU fan (PWM) plugged into the CPU fan (PWM) header. I also have the rear case fan (another PWM fan) plugged into the SYS_FAN2 header. This is a 4 pin fan header and the manual shows the pin out that is close to the PWM cpu fan header but it shows the 4th pin as being reserved? How is my PWM fan going to behave while plugged into this header? Will it be controlled or just run at full speed? Please help.

Hi Erik,

The GA P55 boards are set up with less than completely logical fan control headers. The CPU fan header is a 4 pin header, and if you have a 4 pin connector to your fan, will control the fan speed by pulse width modulation depending on CPU temperature. The Smart Fan CPU has to be "Enabled" in the system setup PC Health tab to do that. If your CPU fan has 3 wires, it will be controlled by varying the voltage on pin 2 rather than by PWM. Pin #3 reports the fan RPM.

Both CPU and System Fans can have the "Fan Failure Warning" feature Enabled in the same section of the system setup to warn you if a fan fails.

The System Fan headers are all different in their function. System Fan #1 has 3 pins, reports RPM but runs at full speed from the MB, System Fan #2 has 4 pins, reports RPM, and runs at full speed and as you said the 4th pin is not connected for PWM, go figure. If there is a System Fan #3 like on the UD7, it does not report the RPM and funs at full speed. The Power Fan header has 3 pins, reports RPM, and runs at full speed, and if you have a PCH Fan 3 pin header it does not report RPM to the BIOS, and has 12V on pin 2. So there are 3 fan headers that report their fan speed to the BIOS.

However, you can use a software fan/temp utility like SpeedFan, or a hardware fan controller unit fitting in a 5 1/4' opening in front or your case where you can contol manually your fan speeds if you want.

Hope that helps & makes some sense
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September 7, 2010 3:36:41 PM

Thanks John. Makes perfect sense and is what I kind of figured. Pretty stupid to set the Sys Fan 2 like that....Will speedfan be able to control or set the speed for that header?

Erik
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a b V Motherboard
September 7, 2010 6:06:12 PM

Hi Erik,

I haven't tried SpeedFan on a P55 board, but it does have the capability to monitor the MB temp sensors, and to control the fan speeds 0-100% which you set. It does that on 3 pin fans by controlling the voltage to the fan rather than by PWM.

I know it doesn't work on all boards.

It is a free download which you can install, check out, and uninstall if it is not what you need. It does measure temperatures and also reads the SMART (Self-Monitoring, Analysis, and Reporting Technology) HDD metadata information as to their functioning

Your MB does show the fan speeds of 3 fans, Sys #1, Sys #2 and the Power Fan. If you have a 3rd Case fan, you can connect it to the Power Fan header to get its RPM readout. That header was used to power the PSU fan, but is not used much anymore.

If the fan noise at full speed is acceptable, better to run the fans at full speed which will keep your electronics at their coolest to "last" longer.
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a b à CPUs
a c 717 V Motherboard
September 7, 2010 9:29:16 PM

Opinion ~ beyond an OEM or simple CPU fan/pump {~H50/70} and perhaps the rear exhaust fan the MOBO is not the ideal place to run fans, and all other 3-pin fans should be run directly off the PSU. In most if not all situations I run fans from a Fan Controller.

Unless the "reserved" can actually control the rear/exhaust fan then it's pointless to connect it to the MOBO; try it and see if the BIOS can control that fan. Other than a software/programable Fan Controller unit I personally won't use a "software fan control app."

In situations where there's OC then I don't want any extra power running off the MOBO, and high CFM fans have no business being connected that way.
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September 8, 2010 2:04:14 PM

Best answer selected by onefastford.
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