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Jumping an AT power supply

heymrdj

heymrdj

Diamond Member
Hey guys, I have an old 250W power supply from a doner system here I'm gonna use to work with hobby stuff. (provide power to the occassional CD drive, test my 12v circuits, that sort of thing). It still runs when I hook it up to an old mobo, but I don't know how to make it come on by jumping the pins to let the power switch work.

P8 is black, black, brown, yellow, red white.
P9 is red, red, red, blue, black, black

AT switch is two wires, plus a green ground that was screwed into the chassis.

I have me some wire ready to stick into the connector, I just need to know what to stick where. Thanks 🙂.
 
No.

AT power supplies use a mechanical switch on the AC side. The button you hit on the front of the case essentially connects the two wires together. DO NOT short those two wires together like you would an ATX power supply's. You will get electricuted.
 
Originally posted by: jonnyGURU
No.

AT power supplies use a mechanical switch on the AC side. The button you hit on the front of the case essentially connects the two wires together. DO NOT short those two wires together like you would an ATX power supply's. You will get electricuted.
Click to expand...

No I realise that's the switch. What I have to do is find the PS-ON wire or something I guess on one or both of those AT connectors and short it to ground, like you short the green wire to ground on an ATX PSU. That way I can just use that switch you referenced to to turn it on and off at will.
 
That switch turns the PSU on and off, there is no PS-ON wire on an AT power supply, only the hard switch.
 
Originally posted by: Gillbot
That switch turns the PSU on and off, there is no PS-ON wire on an AT power supply, only the hard switch.
Click to expand...

But I can only get it to turn on when i hook it up to the motherboard. Something is allowing it to be turned on.
 
That seems to be the case with this one. Oh well, i'll just keep her in the chassis with the mobo. It already tested my lighting kit and switches tonight 🙂.
 
Right. There is NO power on lead on an AT power supply. AT ALL. If the main switch is on, the leads are live and shorting any of them will zap you. Like Zap said, it's probably not spinning because there's no load. That was a common problem with older PSU designs.
 

Modern PSUs have an internal resistor that gets used on startup, then if it monitors load, it will switch the resistor out of the circuit for improved efficiency. Older power supplies don't have this, and may need load on all rails to boot.
 
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