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Processor / Case Fan controller
Installed a fan controller, computer says no fans detected

 10:01 pm on Aug 8, 2005 (gmt 0)

I recently installed a nice fan controller in my computer. It controls four fans; it regulates their speed based on temperature sensors that I installed. Problem is, the computer says that there are no fans detected and will immediately shut down when turned on. This is troubling for me because if I'm out of town or something and the power goes out, my batter will keep the machine alive for a while and then shut down. The computer will turn back on when power is restored. It won't with this problem.

Anyone know of any jumpers or something that I could install on the motherboard fan power / sensors to trick the motherboard into thinking that fans are present? I know they are there for a reason and that the computer would normally shut down on a fan failure, but my new fan controller has a rather loud alarm built in.

Thanks in advance.



 10:03 pm on Aug 8, 2005 (gmt 0)

At least in my BIOS, I know there is a setting that let's me choose whether to shutdown on fan failure or not. If your BIOS has that option, turning it off seems like it would fix your problem.



 6:21 pm on Aug 9, 2005 (gmt 0)

Yeah, I looked there first. Disabling that function is not an option in my BIOS.

Any more ideas?


 6:25 pm on Aug 9, 2005 (gmt 0)

If you could find out the internal DC resitance of the fans you removed, you could always put a resistor of equal value across the pins that normally power then.

Downside would be, ironically, a little more heat.



 6:28 pm on Aug 9, 2005 (gmt 0)

>> Anyone know of any jumpers or something

It's likely the motherboard knows of fans based on the power outlets on the motherboard itself. Different power connectors on the motherboard are associated with different fans and you can work it out by trial and error.

The solution is not simple. You may have the options in the BIOS to turn off the auto-protection that's causing it to shut down. Or, you may be able to attach fans to the power connectors but have heavy resistances to slow the fans down to almost zero rpm.

<added: TJ's solution is obviously better but modern mobos actually monitor the fan speed and if it gets no "reply" from the fan as to the rpm it's running at... you may be back to square one>


 7:24 pm on Aug 9, 2005 (gmt 0)

<sigh> I thought this would be a good solution. Lesson learned I guess. Make sure your motherboard allows you to disable fan monitoring.

I wonder if the mobo uses resistance to measure RPM. If so, a resistor would be a decent solution.

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