fan sense lead emulation

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I have a motherboard that I wish to convert to liquid cooling for
silence.   However, the chipset and CPU fan header inputs must show a
fan speed value to boot.   Without these leads connected the speaker
gives a solid tone.   (I connected the power without the sensor lead to
validate this issue.)
There is no option in BIOS to ignore these speed sensors.
Does anyone know of a simple little circuit that could fool the
motherboard into believing that these fans were running at 2500 rpm?

Re: fan sense lead emulation

I'd just make sue that the fan you use for cooling your coolant radiator has
a sensor and is connected to these headers on the motherboard. AS far as I
know, you can parallel them up, and so run two sensors off of the same

Failing that, just use an old fan, mounted anywhere handy in the case (it
might be beneficial - if you locate it correctly you can blow cold air
across the motherboard voltage regulators, which normally rely on air
spilled over from the CPU heatsink for cooling and will suffer extra heat
stress when you remove this).

PS -  If its too noisy, try the normal speed reduction methods (i.e. 7V
between 12V & 5V rails, 5V, resistor in the lead etc.)

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