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- Aug 28, 2012
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Hi All, this is my first post on the forum. I picked up a PowerMac G5 cheap from work which they were getting rid of. It looks SWEET and works perfectly but is pretty much useless to me as I mainly use Linux, and have only owned a mac for about 12 months, so I don't have a use for a "classic" mac. I decided to do a case mod on it. I'll document it on a different thread. I plan on reusing all the fans, and every piece of information I can find on the fans is incomplete, so I decided to share my findings.
First of all, the commonly known stuff, pinouts. On my G5, the cables are all black so I'm taking a guess as to which one is pin 1:
PIN 1) - Variable voltage power supply (speed control input). This input varies from 3.9v RMS (5v Peak) at minimum speed to a smooth 12VDC at full speed.
PIN 2) - Speedo. This is an output from the fan back to the controller to feedback the fan speed. It is a 50% duty cycle 4.0v square wave which varies from 28Hz at minimum speed to 111Hz at full speed
PIN 3) - Ground (negative)
PIN 4) - 12V (for fan logic?) This appears to be a supply for the speedo feedback circuit and any other digital/control circuits on the fan. I believe they have this separate 12V rail because at the minimum speed the Variable voltage rail dips to about 1.2v.
Now some reference pictures of the traces for the speed control and the speedo feedback. The two square wave traces are the feedback line (pin 2?), one at full speed, one at minimum speed, the saw-tooth shape trace is the power supply rail at minimum speed, and the flat 12v line is the power supply rail at full speed.
First of all, the commonly known stuff, pinouts. On my G5, the cables are all black so I'm taking a guess as to which one is pin 1:
PIN 1) - Variable voltage power supply (speed control input). This input varies from 3.9v RMS (5v Peak) at minimum speed to a smooth 12VDC at full speed.
PIN 2) - Speedo. This is an output from the fan back to the controller to feedback the fan speed. It is a 50% duty cycle 4.0v square wave which varies from 28Hz at minimum speed to 111Hz at full speed
PIN 3) - Ground (negative)
PIN 4) - 12V (for fan logic?) This appears to be a supply for the speedo feedback circuit and any other digital/control circuits on the fan. I believe they have this separate 12V rail because at the minimum speed the Variable voltage rail dips to about 1.2v.
Now some reference pictures of the traces for the speed control and the speedo feedback. The two square wave traces are the feedback line (pin 2?), one at full speed, one at minimum speed, the saw-tooth shape trace is the power supply rail at minimum speed, and the flat 12v line is the power supply rail at full speed.