Nvidia Quadro RTX4000 - FAN at max RPM

[TipSerw]

Hello, I have a Quadro RTX 4000 graphics card with a FAN problem.

The fan immediately spin up to 100%. I checked the TACH pin on the fan connector, and there is a direct short(44Ohm) to ground. With the fan disconnected, the short is still present, so the issue is on the PCB, not in the fan itself.

I traced the TACH line and checked the nearby pull-up resistors — they all seem fine. There are no visible burned components. Close to the fan header there are chips like NCP45491, uP9512R, and uP1666Q, but as far as I know, they are VRM/power monitoring controllers, not fan controllers.

I suspect either an ESD protection diode, a small capacitor to ground, or the actual fan controller input pulling TACH low, but I can’t locate the exact cause of the short and I also can’t find the actual fan controller on this PCB.

Has anyone worked on these RTX cards before and can point me to where the TACH line usually goes, or which component is most likely to fail and short the line?

Any advice or schematics/boardview references would be appreciated.

Thanks in advance!