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Chuckaluphagus
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CPU fan sensor failed with an annoying 1 Hz pulsing

Thu Dec 27, 2018 5:49 pm

I just had a new (to me) failure to track down. My desktop computer started making a very, very annoying pulsing fan sound at about 1 Hz, so WHIRR-whirr-WHIRR-whirr etc. I opened the case and found it was the CPU fan, the default fan that came with a CoolerMaster 212 three years ago. Rebooted, found that it was doing the same thing in the BIOS menus, so not a fault of the operating system thermal management.

In the BIOS, the fan speed for the CPU fan wasn't showing up at all. The fan was still running - obnoxiously so, even - and the CPU temp was fine, but clearly something was wrong with either the RPM sensor or the motherboard. To my luck, I had exactly one spare 100 mm fan lying around, and using that I could determine that it was the old fan's RPM output that had failed, and not the fan header on my motherboard.

I have to say, that's not a bad failure mode: the motherboard couldn't detect the fan speed anymore, so it started pulsing the fan speed up to ensure cooling and make an audible nuisance of itself. Now I just need to order a couple more spare fans for future situations.
 
just brew it!
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Re: CPU fan sensor failed with an annoying 1 Hz pulsing

Thu Dec 27, 2018 6:12 pm

That's really weird/interesting. The RPM output must've been sending something weird that was confusing the motherboard (as opposed to not sending anything). Otherwise, I would've expected the motherboard to just treat it like a fan that doesn't support RPM sensing.
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Waco
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Re: CPU fan sensor failed with an annoying 1 Hz pulsing

Thu Dec 27, 2018 11:34 pm

That's at least a good failure mode on the motherboard's part. That, or full speed, would be good choices. The changing speed alerted you, so I'd say that's an excellent choice on the part of the board firmware.
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just brew it!
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Re: CPU fan sensor failed with an annoying 1 Hz pulsing

Fri Dec 28, 2018 7:39 am

Waco wrote:
That's at least a good failure mode on the motherboard's part. That, or full speed, would be good choices. The changing speed alerted you, so I'd say that's an excellent choice on the part of the board firmware.

It may have even been a (lucky) accident that wasn't intended by the firmware designer...
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Chuckaluphagus
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Re: CPU fan sensor failed with an annoying 1 Hz pulsing

Sat Dec 29, 2018 3:43 pm

just brew it! wrote:
Waco wrote:
That's at least a good failure mode on the motherboard's part. That, or full speed, would be good choices. The changing speed alerted you, so I'd say that's an excellent choice on the part of the board firmware.

It may have even been a (lucky) accident that wasn't intended by the firmware designer...

If so, it's a very luck accident to work out that well.

For reference, the board is an Asrock Z97 Extreme4.

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