I have an old recycled server (about six years old) that I pressed into emergency service due to a hardware failure a few weeks ago. But it’s loud. So I got some replacement quiet fans for it. Much cheaper (and, I hope, more environmentally friendly) than buying a new system. But there’s no standard for wiring for fans, and the datasheets don’t all agree.

I borrowed the PWM controller my son and I assembled as a dimmer for the LEDs in his halloween costume, added a pullup resistor, and used it to discover that the server system fans, though they are almost identical parts to the power supply fans, have different color codes for their wires. And the datasheet for the server system fans is backwards.

Trust, but verify. ☺

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