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The internal sensor for the motherboard is giving out an invalid value for the temperature, causing the fan to go on full. The computer is exactly 10 days out of warranty.

It's a 4 Pin 12v PWM fan. Is there anything I can do to manually control the speed myself with a potentiometer, or can I use a third party PWM controller mounted externally?

The fan would barely reach 50% when working properly. Currently computer is simply too noisy to be used. All other software/bios fixes have been applied but have not worked.

4 pin connector on motherboard

Fan

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    \$\begingroup\$ Last resort hacks: Some fans will spin slowly if PWM is connected to ground, but others will completely stop. 50 % can ve achieved by connecting RPM and PWM together, but some fans may require some help to start up. \$\endgroup\$
    – Oskar Skog
    Apr 18 at 12:49

2 Answers 2

Reset to default
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After trying every possible reset method of the bios, all of the methods reporting that the bios had been reset - this still made no difference. However, removing the bios battery for 20 mins has cured this fault.

The bios did not report that it had been reset, but now the fan is back to normal.

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I'm glad you have found the solution on your own and shared it with us (much appreciated).

I was going to suggest the simplest solution: a few (let's say 6) standard rectifier diodes (like 1N4001) in series with the +12V wire (should be the yellow wire in your case) to reduce the voltage and slow it down.
You would have to cut the yellow wire and insert the diodes in series (cathodes towards the fan).
Many of the fans, especially the 3-wire models, could be slowed down like this, as they are controlled by the amount of DC voltage applied to them.
Your type may not drop its RPMs with reduced voltage, but it should. The devil is in the details of its internal circuitry and whether the coils can work just fine (full RPM) at a lower voltage.

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    \$\begingroup\$ I know it's odd, but I would of got more satisfaction for myself if I had to try your suggestion - Removing a battery just isn't quite as much fun! - I can only assume the pwm controller isn't part of the bios but something separate that still needs to hold information.... \$\endgroup\$
    – JohnnyVegas
    Apr 18 at 13:49
  • \$\begingroup\$ @JohnnyVegas I know how "painful" it can be to just get to the BIOS battery or CPU fan, or just open up a laptop in general. That's why I hate working with them. Almost always there is an extra or a lacking screw, or screw holders don't hold anymore or they break off. \$\endgroup\$
    – Edin Fifić
    Apr 18 at 14:09
  • \$\begingroup\$ @JohnnyVegas: According to your question, the problem was with the temperature sensor circuit, not the fan PWM. 100% speed is the correct thing for a fan controller to do when the temperature is reported too high. \$\endgroup\$
    – Ben Voigt
    Apr 18 at 20:54
  • \$\begingroup\$ @BenVoigt He's well aware of that, he just wanted to circumvent it knowing it's a false reading. \$\endgroup\$
    – Edin Fifić
    Apr 18 at 21:01
  • \$\begingroup\$ @EdinFifić: Yet he commented thinking that removing the battery made the PWM fan controller reset some memory. \$\endgroup\$
    – Ben Voigt
    Apr 18 at 21:04

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