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PC Power Supply? Answered

Hi Guys! I need some help.
I recently got several pc power supplies and I don't know how to turn them on. That sounds stupid, but I don't really work with them much. I tried plugging it in expecting the fan to at least turn on, but nothing happened. No outputs from any of the leads either. What am I doing wrong?



If you've got no green wire to turn the supply on, it may be an older type which needs a load on the 12V rail to get it working. Connect a load to it (e.g. CDROM drive to one of the connectors) to test it. If you're building a bench PSU, connect a 100 ohm 2W resistor between yellow and black wires.

Which ones? There are 3 yellow wires.The black are all grounds, I know that, but which one should I ground? There is also a purple wire if that helps at all.

All the yellow ones will be the same voltage - any one will do.
However, this is sounding like it isn't a normal PC power supply. Did it actually come out of a computer? Can you describe it in more detail - How many rows and what colour goes where. (A picture would be best.)

Well, actually I think it may have come from a server. Its about 1200 Watts, and a normal pc power supply is about 200 - 400 or so. Here is a picture, kinda grainy, but it may help.


It does look rather meaty, and there are usually more output leads than that.  See if you can track the connector down HERE .  There are also a fair few non-standard ones around - Dell, Compaq and others come up with their own connection schemes for certain machines.

Well, that website allowed me to identify most of the connectors, but there is still one or two that I'm trying to track down. If you could pass on any other help that would be greatly appreciated!


your doing everything wrong

I assume these are all ATX psu's. AT psu's were wired differently and had a separate connect for an on/off switch. You need to get a schematic of your psu's first!. Be careful!!!! https://www.instructables.com/id/Atx-to-At-ps-test-cable/ might help. ATX motherboards need a momentary switch and AT motherboards and contiguous power need a toggle switch.

When I made a bench top power supply from an ATX PC power supply, I used this instructable.  It turns out that there's a green wire you have to snip and solder to a black wire, details are in step three of that 'ible. 

My understanding is that when the supply is installed properly in a computer, this connection is made automatically.  It's a safety feature designed to prevent people from doing what you're doing, turning on the power supply when it's not attached to a computer!

Its not a "safety feature" its how the PC is turned on when you press the button !

I've seen that instructable, but unfortunately there is no green wire. Theres not even one of those giant pins. There are 8 smaller ones labeled P1-8. Any ideas?