Hi all,

I have recently acquired a couple of cheap Pentium Overdrives from CPU-World seller that came without heat sinks and fans (this was the main reason for low price). As you might know, these CPUs sense fan and drop to 1X multiplier if fan is not detected. I wanted to volt-mode them for 4V and try to overclock them, so 1X multiplier did not fit my concept.
i've been searching all over the internet and was unable to find any solution on how to fool the CPU and make it think the fan is attached.
I spent a few hours trying to track signals from 3rd fan wire of my other PODP5V with its original fan attached using oscilloscope.
I was trying to send PWM square waves on different frequencies from an MCU to this wire.
Nothing worked. The reality was as simple as hell.
So there are 3 contacts on the CPU itself that connect to the fan. 2 of them are +5V and Ground, one can easily trace them with a multimeter.
The 3rd remaining contact is the fan sensor, and it needs to be pulled to ground via a 5-10 kOhms resistor in order for the CPU to detect working fan. As simple as that!.
I hope someone will find it useful.