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HP Recommended
Z640
Microsoft Windows 10 (64-bit)

The Z640 rear fans are running 2500RPM and they are very loud. I measured 80dB

 

Here are my troubleshooting so far:

  • The fans are ok, PWM works
  • The motherboard is ok, PWM regulation works.
  • I can set the speed to maximum in bios, so PWM works.
  • The ambient sensor is good, 25 Celsius.
  • CPUs are cool, 52 Celsius.
  • I tried CMOS clear.
  • I tired fresh Win10Pro install.
  • Installed the earliest and latest BIOS, same RPM.
  • Tried CMOS clear with fresh Win10Pro, it seemed like the fans were quiet for some time but when install finished, they still ramped to 2500RPM.
  • When 100% CPU utilization, the fans don't spin up? I get 800RPM at 100% and 80 Celsius.

I googled everywhere and I can't find nothing else to try.

 

The rear fans are the same as the CPU0 fan, so the rear fans are able to run in 400RPM.

 

I noticed there is power connection for Memory Fan Baffle on motherboard and case has attachment holes. So perhaps the BIOS thinks the Memory Fan Baffle is missing and tries to compensate by ramping up the rear fans. 

 

To conclude, it seems like some simple BIOS bug where the fan curve is messed up for some reason

 

Here is the "normal" HP Performance Advisor. The configuration warning is about missing some memory modules.

 

Hp z640 extreme fan speed.jpg

 

 

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