How to turn on an ATX PSU

Well, it's supposed to be cold and nasty here this weekend, so I thought I would experiment with a radiator & fan/s setup.

SO I put my spare ATX power supply on the
workbench, and hooked up a 12 VDC fan. I turned on the main switch, then shorted pin 14 of the MoBo connector to GND, power supply didn't come on. I figured when you pressed the power switch on an ATX machine, the switch was just shorting pin 14 on the main power plug (labeled turn power supply turn) to GND. Obviously not.

So, I have two questions. Is it OK to run the ATX PSU with no load on the +5 VDC, - 5 VDC, and -12 VDC, and only a light load on +12 VDC?

If so, what do you have to do to get it turned on when the PSU is laying on the bench?

Pudge

Never mind, I found this.

ATX Chassis:

Why the computer/fan does not turn on after I flipped the power switch to ON located on the ATX power supply? ATX power supply is different from AT power supply. It depends a logic circuit on the motherboard to turn it on. Once you flipped the power switch on the ATX power supply to on (some AX power supplies do not even have such a switch), the ATX power supply sends a 5V 720MA current to the motherboard through pin 9 on the power
connector. That current is for WOL (Wake-up On Lan) and power on circuits. There is a power-on jumper on the motherboard that connects to the pushbutton located in front of ATX case. When the pushbutton is pressed, it sends a signal to the mothboard, which in turn notifies the ATX power supply to turn on the full power. The location of the power-on jumper on the motherboard is manufacture dependent. You will need to read your motherboard manual to locate that jumper.

At any event, do not try to manually jump-start the power supply without attaching motherboard. Since the power supply is expecting certain sensing circuit feedback to regulate the output voltage, manually starting it without attaching it to the motherboard could cause damage to the power supply. (OOPS, I already did this, hope I didn't blow it up!).

Pudge

If you did it like this:


and your PSU didn't work, its a problem with that PSU. Many lower budget PSUs have this problem. I have often used the jumper means, successfully.

I thank you for that sir as I was looking for that information. Knew it was around somewhere, just did not know where. Will this get full voltage/amperage on the 12v rail?

Never tested the amperage, but I have powered up fans, drives, and accessories with this method for out-of-case testing.

you need to put a load on 5v lead most people use a resistor to get full amps

stool said:

Never tested the amperage, but I have powered up fans, drives, and accessories with this method for out-of-case testing.

Click to expand...

I've done the same. The radio at work doesn't have a CD player, so we usually just grab my test CD rom and PSU short the leads on the PSU and plug in a set of speakers, when we get tired of listening to really bad talk radio. It's usually the green wire you need to ground. I think all ATX PSU's have standardized wire colors, but I could be wrong.

Thanks everyone for your responses. I will have to experiment around some more. I knew there had to be a way to do this.

Pudge

Just be careful.

CrystalMethod said:

I think all ATX PSU's have standardized wire colors, but I could be wrong.

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I wish it was that easy. The Enermax has pin 14 green, the Leadman Powermax has it grey, and a couple of generics I have sitting around both have different colors. The easiest way I found to do this is to look at the connector with the pins facing away, clip upward, and use the fourth pin from the right.
An easy way to avoid jumping pins at all is to go toPC Power&Cooling , and get an ATX power supply tester. For $10, it comes in real handy.

Stool

The ATX power supply tester looks cool!!!!

I also noticed the 1 amp load resistor for the +5 VDC line. Between the two a fella ought to be able to safely do some bench testing.

Pudge
I noticed the witty sayings in a lot of sigs,
here's a bit of wisdom I've picked up over the years.

He who farts in church
often sits in his own pew.