When experimenting to bypass the detection. I use 10 to 47 ohms resistors to ground these detection pins. I had to do this to my proliant 1500 and many Dells using 3 pin fan which they do not use tach for this. They ground one pin as long as fan is working but I don't have any dell fans and don't like their choice of dell fans. Ditto to HP in general when I had to learn to ground unused or non-HP connectors using HP boards in generic PC, not just for fans.

Cheers,

pentiumspeed wrote on 2021-09-15, 17:37:

When experimenting to bypass the detection. I use 10 to 47 ohms resistors to ground these detection pins. I had to do this to my proliant 1500 and many Dells using 3 pin fan which they do not use tach for this. They ground one pin as long as fan is working but I don't have any dell fans and don't like their choice of dell fans. Ditto to HP in general when I had to learn to ground unused or non-HP connectors using HP boards in generic PC, not just for fans.

Cheers,

Thank you for your answer.
It is possible bypass the POST detection. But as Overdrive can become hot, I choose to made an adapter from a male 3-pin fan to the plug used by the 486, replacing the original 40x40x20 fan by a Noctua. Very silent now with a stronger airflow and classic fan compatibility in bonus.
But my question isn't to bypass the detection, but what is the fan pinout of a Vectra VL/500 model 515?
I can detect the pin(s) grounded.
Then check the voltage.
If +12V on pin one and pin 2 is grounded, the pin are identical in both machines.
But for the rest....
Maybe there is a way to detect a PWM signal with an oscilloscope and be sure it is that.
But for the pin that are originally bridged (3 and 5), if I try that and it's different, I can create a short circuit and bye bye the computer.

I said again, your HP does not use PWM to control fan rpm or tach for reading fan speed at all for this vintage.

My compaq Proliant 1500 and Deskpro XL used 4 and 5 pin fan connectors, yet they only used three or four pins and they still used grounded system when fan is working.

What you *will* need is find the correct pin for fan failure detect signal from fan on that motherboard and ground that permanently. Nearly all these vintage computers including Dell using PIII that use more than 3 wires or more will be fan failure signal that is grounded by fan when fan is working. If fan fails, the signal is left floating and this will alert the computer's of a fan failure.

Vintage fans with this type is very hard to find anymore so you like me had to make adapters or rewire the connector correctly when using newer fans.

Cheers,

Hi @pentiumspeed. A lot of time has passed since I opened this thread. A few month ago after having made my measurement I find that and I built an adapter to use a classic fan connector with a 10 ohm resistor to bridge the pins 3 and 5: the fan and the computer are working fine since then. But I still don't know what is the purpose of the 4th pin though as I couldn't get anything from it. The idea of the thread what to identify them all, so maybe someday, someone will tell.
Anyway thank you for your help, it was really helpful 😀

Exactly, and welcome, cheers