Help with 6 pin fan head / mod to 4 pin

[ins0mniac]

Hi All,

I'm new to all this so bear with me, I was going to post in the DIY section but that is locked...

I've picked up a HP DL120 G6 rackmount server and the fans on this server are expectedly very noisy and I can't find any quieter 6 pin fans to directly replace them with.

So, this brings me to my task of either modding a 3/4 pin fan getting it to work or using a fan controller to lower the voltage and drive the existing fans. (though I'd prefer replacing them)

The dual fans (12v 1.86A) and pin out looks like:

The pin out:

Pin #1 - Orange = open-collector tachometer
Pin #2 - Black = ground
Pin #3 - Red = +12 VDC
Pin #4 - Blue = ground
Pin #5 -Yellow = open-collector, low-pass/high-fail, trip-point (speed) and locked rotor alarm
Pin #6 - Green = PWM - pulse-width modulated speed control

I've already tried connecting a 3pin fan to the board (12V to Pin3, Tach to Pin1 and Ground to Pin2). The result of this was the Fan spins at start up but the server complains about a failed/missing fan and refuses to continue.

My research tells me the culprit could be Pin 5/Alarm needs to be driven to 0v to tell it everything is ok. Can someone advise how this should be best done?

I tried a wire from pin 5/Alarm on the board to the computers chassis in hope this would do it, but it didn't work, was abit of a flimsy connection though.

If anyone has done anything similar or can advise of a solution / technique to get 3 or 4 pin fan connected to the board it would be highly appreciated!

Thanks