Fake tach signal questions


Sep 23, 2010
I purchased a Lenovo G7028 not too long ago and while it works great, the noise has been driving me nuts. I've been playing around with different fan configurations but the switch requires at least 2 of the fans operating at the RPM (3 fan ports total, 2 will allow the switch to run but will still post with a fan error message). Currently, i have one of the fans running and bridged the tach to one of the other ports and have 2 120mm fans on top (700RPM).

The 40mm fan in question is a Delta that spins at 9000RPM according to this PDF

Tried running a 8000 RPM Nidec fan, and the fan error light still comes on so i suspect it has to run at 9000RPM for all three tachs in order for the error message to go away.

I started with this thread Generate Fan RPM Signal W/O Fan and then read this

I'm not too familiar with calculating this information but i do believe i have a general understanding; i need a device that can generate a fake RPM signal with either an adjustable range or buy something fixed. Honestly the adjustable one sounds much easier to tinker around with, but even then i'm still not sure what to buy. Building wise, i've done resistance/amps/voltage calculations before but that was over a decade ago, and currently i don't own a soldering iron.

If someone wants to build it for me, PM me and let me know the costs.