Hi,
I'm having some trouble with my X1C3 (20BS): While using I noticed the system getting considerably hot and throttling down. On closer inspection I noticed the fan didn't spin at all, which shouldn't happen at these temperatures. Since the system looked clean I suspected a power management bug and rebooted, now the system gets into POST but shuts itself off before accessing the bootloader due to "fan error". Resetting using the "hidden" button or cycling power (including battery) didn't show any change.
After opening the system I noticed corrosion on the fan connector - not quite unusual over here, probably due to wet climate since it's only around the air intake. Sadly the connector itself measures fine after some cleaning - I get 5V at the fan and the fan motor works fine in another 20BS. All digital lines (PWM control, speed sense and one I couldn't identify) are however shorted to ground at the mainboard side. The working 20BS shows a .4-.6V diode drop on these lines.
Whatever IC controls/monitors the fan seems to be broken. I couldn't find and schematic so far and following traces doesn't quite work on multi layer boards. So while I try to identify allICs and hope for something useful: Has anyone an idea which IC controls the fan or if there is a way to bypass the forced shutdown?