Power unit stops working when plugged in to mother board


I am installing a new power unit in a desktop PC. The unit works fine (Fan turns!)when not plugged into motherboard. As soon as it is plugged in to motherboard it stops (Fan stops!).

What is the solution?

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Kyle SchroederEndpoint EngineerCommented:
Ensure that the Voltage switch is set appropriately for your country (either 115 or 220V).

You're not plugging it in while its on are you??  I doubt it, but you never know!

Are the POWERSW and PWR_LED leads from the case connected appropriately to the motherboard?

First of all, you should not plug in a running power supply to a motherboard.  I assume this is an AT style power supply for an older motherboard?  Otherwise you would not normally be able to get it running without the switch logic on the motherboard.

"What is the solution?"

What possessed you to plug in a running power supply?
See the above - try connecting to MB first, then connect mains power... If still no luck try PSU on another MB, if possible. Or the other way around, to see which one is at fault.
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To start up ATX power supply, connected to the MB you must connect PWR ON switch to the MB.Without it you cant start the PC.
It sounds as if this person wants to fry the mobo and possibly get electrocuted.  Maybe the question was just worded incorrectly.
SophMarceauAuthor Commented:
Hi Everyone

Thanks for the tips. No I did not connect the power supply to the motherboard when the power switch was on!!! As Slink9 said I worded the question wrongly.

What I have noticed is that there are 2 connections to the motherboard. If I plug in both no response. If I just plug in 1 then there the fan turns and the disk lights come on. A soon as the 2 connections are plugged in and I SWITCH on the unit nothing happens.

I do not have another MB or PSU to try out.

Any more ideas please


Are you hooking the connectors "black on black"?  There are two black wires on each power connector.  Make sure these are both on the inside, hence the term "black on black."  The four black wires should be in the middle of the power connector.  If you have hooked them up backwards you may have fried the mobo and/or cpu.  Maybe not.
SophMarceauAuthor Commented:
To 1175089 how do I connect PWR switch to the motherboard. The Power On switch is part of the Power Supply unit. There is one of these old locks on the side of the PC. Ther is 2 wires coming out of the lock unto the mother board.

Thanks for your interest 1175089

If you have two power cables, disregard that.  You don't have an ATX power supply.
This seems to be an AT PSU. The power switch should not be connected to the MB. The lock you mention is probably the keyboard lock. There are pins on the MB that are used for this connector. It could be left unconnected. The power switch normally will be mounted somewhere on the inside of the front panel, behind a button or so.

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What kind of power supply do you have ? (For Baby AT or ATX MB)? Some ATX power supplyes has a swith on it's back.
AT power supply connector (12 pin block)has two plugs, with six wires each.Two of them are black. ATX power supply connector (20 pin block) connects to the MBin only one waybecouse it has different hole sizes.
SophMarceauAuthor Commented:
Thanks everyone. I am sure now from what you all say that I have an AT PSU. I will check for another switch on the front of the PC. The panel was removed when I got it so there were no buttons to be seen. I will check the PC on Tuesday when I return to work and let you all know how I get on.

Thanks again all

SophMarceauAuthor Commented:
Thanks all. Success!
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