Question CPU fan only spins when plugged into sys fan

Oct 27, 2021
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I tested all the pins CPU1 CPU2 and sys fan with a different fan. They all seem to be working fine. The cpu fan only runs if plugged into the sys fan. How can I fix this?
 

Paperdoc

Champion
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A few items to check

1. Do you have your CPU_FAN header configured in BIOS Setup to use a fixed slower speed, rather than automatic speed control?

2. Watch that fan carefully as soon as you turn on the system. Does it start up, then shut down again in a few seconds?

3. Check the MODE setting of the CPU_FAN header. IF your fan has FOUR wires to its connector, which has 4 holes in it, the header should be set to use PWM Mode. IF the fan has THREE wires and holes, then the header should be set to use Voltage Control Mode (aka DC Mode).
 

Karadjgne

Titan
Ambassador
Does it spin ever? All fans, mode regardless, should spin up at post, it's only when bios is active or OS that there's any controlling curves.

Once mode is established as paperdoc explained, min/max needs to be set. Not all fans are the same and after post, when bios starts the fan curve, if the fan needs a certain pwm % or voltage to start and the minimum is too low, the fan won't spin. Not enough juice.
 

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