SYS_FAN low voltage

[geohei]

Technical (newbie) question.

Gigabyte GA-Z77X-UD5H
SYS_FAN1 says pin1 = GND and pin2 = 12V.
I only measure 7.72 V, resulting in a fan (3 pins) speed of 550 RPM i.s.o. #1000 RPM.
The BIOS doesn't show any settings to be modified in order to change voltage on SYS_FAN1.

Here the manual:
http://download.gigabyte.eu/FileLi [...] ud5h_e.pdf

Page 27 says that pin2 is "+12V/Speed Control", but I don't see any possibility to change the speed (neither in BIOS, nor manual).

Is this motherboard hardware problem or do I miss something?

Thanks,

[mikeyb5753]

Fan speeds are automatically regulated according to temperature.  in most cases this can be overridden in BIOS

[geohei]

This one isn't. It's taking pin1 and 2 as constant 12V and regulates accoring a switch (3 levels) on the fan.

The problem I mentioned is the voltage of pin2. The manual says "+12V/Speed Control" but the measured voltage is 7.72.

How can I change the voltage (if I can)?
Has the motherboard possibly a defect?

Thanks,

[absic]

Hi there,

In BIOS go to the PC Health Status section.
 In here you should find the Fan Speed Control.
By Default, this will be set to Normal which means the Fan Speed will be adjusted according to System Temperatures.
If you want to run the fan(s) at full speed then set this control to Manual and then adjust the speed settings by using the Slope PWM settings.

[geohei]

You are perfectly right, but AFAIK this setting only applies to 4 pinned fans. Mine is 3 pin only, hence the "Speed Control" pin4 isn't connected to the fan. So, the "Manual" setting doesn't do anything to any of the 4 fans connected to SYS_FAN1/2/3/4 since none uses pin4. I can even go up to "2.5 PWM value/°C" ... no change in fan speed!

However, when starting up the PC, SYS_FAN1 starts with 380 RPM and gradually reaches 600 RPM after 5 minutes. I have the impression that the voltage on pin2 is linked to the CPU temperature (or any other temperature)?

... later ...

I noticed that setting "1st/2nd/3rd System Fan Speed Control" to "Disabled", I get my 12V !!!

Thanks for the kick!