@nophead: If I connect Noctua +5V (yellow wire) to Arduino +5V, Noctua GND (black wire) to GND and Noctua PWM (blue wire) also to GND, the fan stops spinning. I guess, that "PWM connected, but no Voltage" is interpreted by the fan as 0% duty cycle, whereas "not connected at all" means full speed. I think that this is the intended behavior, so the fan seems to be okay. @Zgembo: I have the same board revision (printed on the PCB) V8 Bolt. BIOS part number is identical as well. I have Firmware / Library Version 0.16 / 0.19 for the embedded controller and Firmware 1.06 R.C. 4 for the BIOS. I only have a simple multi-meter tool at hand, but I do measure 5V between Bolt CN7 Pin 2 (middle, PWM?) and GND in every situation so far. Even when I set the duty cycle to 0 in the BIOS. I would have assumed that this voltage would be a flipping between 0 and 5V in a square waveform and that the multi-meter then averages out to some intermediate value. In the extreme case of duty cycle 0, I would have assumed a flat 0V. But that may be an issue with the multi-meter to be not precise enough. I have no oscilloscope at hand, unfortunately.