Quote from: NotFuzzyWarm on June 07, 2018, 02:06:02 PM

Yes voltage in is a constant 12v.
Intel's 4-wire PWM fan spec http://www.formfactors.org/developer/specs/4_Wire_PWM_Spec.pdf

Quote

3.3 Fan Speed Response to PWM Control Input Signal
The PWM input shall be delivered to the fan through the control signal on Pin 4 (see Section
2.1.4). Fan speed response to this signal shall be a continuous and monotonic function of the duty
cycle of the signal, from 100% to the minimum specified RPM. The fan RPM (as a percentage of
maximum RPM) should match the PWM duty cycle within ±10%. If no control signal is present
the fan shall operate at maximum RPM. See Figure 3.

LOL. I tried it on my oldest S9 and once I cut the blue wires, the rear fan ran at full RPM and the front fan at 1320 RMP (I assume that was the minimum RPM). I got this early S9 used, so it's possible that those are not the original factory fans.

I think the simplest way to make these older S9s cooler is to replace the fans with the new ones Bitmain uses on the newest S9s... they seem to be much more efficient.

The one side effect of my experiment that may be useful info for others as well: I confirmed that the front fan has the lower RPM. At least on this specific miner... I have several different generations of them so I may check the others as well, but I assume this should be consistent.