[SOLVED] CPU Fan Won't Stay on.

yourender

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Aug 26, 2015
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So long story short after meddling around in BIOS trying to fix one part of the PC the CPU fan won't stay on longer than a few minutes, almost always just a few seconds at the most. I have tried resetting BIOS, pulling the CMOS battery while the PC wasn't plugged in, cleaning the fan, and tried software to manually force the fan to speed up, anyone have any ideas?

Thank you and have a blessed day
 

Karadjgne

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Well, if it was a DC fan in pwm mode, it'd spin 100%. So it's not that. You checked connections, so not that. Discarded software, so not that. Bios should be set right with reset, mode is checked, so not that. Only thing left I can think of is the fan itself. Either the fan or the motherboard.

Unplug the fan nearest to the cpu header, one where the cord will reach. Swap it with the cpu fan header. That'll put sys_fan blowing on cpu cooler and cpu fan as something else. Turn on the pc.

If it's the actual cpu fan is bunk, it'll not spin again, and it should be, set up on the sys_fan header which you know works. This'll mean the fan on the case should be running, so the bios/motherboard is good. If the fan on the cooler spins, but the case fan doesn't, the cpu fan is good, but bios/motherboard is not. Somehow, somewhere
 

Karadjgne

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You can't shut off the cpu fan in any bios, the cpu won't allow it no matter what you do to the curve, it'll always spin at minimum speed at the very least.

That said, there is a way to mess the fan itself up inadvertently. You most likely have a pwm fan. Many pwm fans don't operate below @ 9vDC. So if you changed the fan mode from PWM or AUTO to vDC/Voltage mode instead, then when windows starts to load and applies a fan curve set lower than 9vDC (that's @ 70% duty cycle) which would be normal for idle speeds on the cpu, the cpu fan cannot spin.

Most software will register that there's a pwm fan on the header, and will change the pwm signal accordingly to change speeds, but on DC mode, the fan won't get the 12v necessary to allow the fan to spin.

In bios, check the Mode setting for the fan.
 

Karadjgne

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Set it for pwm/auto.. .

Yes, it's possible for SpeedFan to mess with it, if you changed SpeedFan parameters, which you did only after the issue started. But even if SpeedFan was set to the wrong address for the cpu sensor, and reads a negative number, the fan would still run at minimum rpm. If you disable SpeedFan, so that it doesn't automatically startup with windows load, then it can't affect the fan profile until it does, bios/windows will set profiles until software changes them.

There is no switch in any bios to turn off a cpu fan. There's eco modes, silent, performance etc but none will set a duty cycle to 0%. DC will usually only go as low as 40% (5v) and pwm might see 20% (still 12v), but even graphic fan curves will have a flat line minimum rpm. Sys_fan headers can have the ability to go to fanless mode, but that'd require the cpu fan itself to be hooked upto a sys_fan header, not the cpu_fan header. That would explain lack of changes by software, as the software would be trying to change the cpu_fan header parameters, not the sys_fan headers. I'd visually check that the cpu fan is actually on the cpu_fan header and correctly mounted.
 
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yourender

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Aug 26, 2015
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It is in PWM mode, I uninstalled SpeedFAN, checked that it was plugged in right and it still isn't working, do you happen to have any other ideas, and I really appreciate all the time you're putting in to help me so thank you very much
 

Karadjgne

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Well, if it was a DC fan in pwm mode, it'd spin 100%. So it's not that. You checked connections, so not that. Discarded software, so not that. Bios should be set right with reset, mode is checked, so not that. Only thing left I can think of is the fan itself. Either the fan or the motherboard.

Unplug the fan nearest to the cpu header, one where the cord will reach. Swap it with the cpu fan header. That'll put sys_fan blowing on cpu cooler and cpu fan as something else. Turn on the pc.

If it's the actual cpu fan is bunk, it'll not spin again, and it should be, set up on the sys_fan header which you know works. This'll mean the fan on the case should be running, so the bios/motherboard is good. If the fan on the cooler spins, but the case fan doesn't, the cpu fan is good, but bios/motherboard is not. Somehow, somewhere
 

yourender

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Aug 26, 2015
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I just looked at the motherboard and both sys_fans are too far from the CPU and I couldn't for the life of me findf another. I'm not sure where the connect is that Nuwan is talking about because it is a cyberpowerpc computer and i dont know much about the case. I think I'm gonna just breakdown and buy a new CPU fan.
 

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