I pulled this off of what I think was a Socket 7 cooler but it may have been for a 486.
The fan is interesting because the ground pin runs off to a separate connector that is meant to be plugged in somewhere. How is this meant to be plugged in and why didn't they just use the ground pin on the molex connector?
Heh are you sure that pin didn't just get pulled loose from the molex? Those adapters are quite flimsy...
It's for motherboards that had limited current available at the motherboard fan header, but nevertheless throw an error if a fan is not connected, or they can't sense that it is turning.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.
jakethompson1 wrote on 2021-09-26, 01:54:Heh are you sure that pin didn't just get pulled loose from the molex? Those adapters are quite flimsy...
I pulled the 12V from the molex. The question is why the ground pin is on a separate header.
BitWrangler wrote on 2021-09-26, 01:54:It's for motherboards that had limited current available at the motherboard fan header, but nevertheless throw an error if a fan is not connected, or they can't sense that it is turning.
They can still sense that a fan is connected by the ground pin alone?
Are you sure that's the ground pin, from the orientation of the connector, it looks like the PWM pin
Definitely the ground pin of the fan, but that looks like a 4 pin header connector.
DO NOT plug that in to a modern system, as it looks like it would connect the PWM pin through the fan, probably not good for the motherboard!
There are only two wires that come off of it. The other one connects to 12V so this is definitely the ground pin. I tested this on my bench supply to confirm.
It's a keyed four pin Dupont connector with only one wire in it for ground.
My best guess:
Early fan control worked via a transistor that would enable or disable the ground connection for the fan headers. That was mainly so you could switch off fans during standby.
If you wanted your fan running directly from the PSU you couldn't choose wether the fan would spin during standby or be shut off. With this adaptor you can hook you fan up to +12V directly on the PSU and still use fan control.
I know, it sounds kind of inelegant but it's the best theory I have.
That sounds like a good theory. And it would fit the time period if it was paired with a 486 with an AT power supply.
