Strange PSU problem

[mysts]

motherboard= Asus P5GC-MX/1333

Problem is PSU stays on all the time

I was doing some paperwork when the computer suddenly turns itself on. No one touched it, it came on by itself. It did not boot up and there was nothing on the monitor but the fans were working.

The following had no effect:
Unplugged the reset button from the motherboard
Unplugged the power on button from the motherboard

The following did have an effect:
Unplugged the 20 pin power plug to the motherboard. The PSU did not turn on.

This computer has performed faithfully for several months.

Anyone have any ideas?

[KBeee]

Using scientifically rigorous research (gleaned from modern TV) I conclude you need the Ghost Whisperer!

Failing that, have a look at your BIOS and OS for wake up settings.

[mysts]

Thanks for your reply KBeee,

As I said in my first post-nothing appears on the monitor so therefore no BIOS not nothing.

[KBeee]

Yes, you'll have to boot your computer yourself to get into the BIOS screen to check your wake up settings. Then you can check your Vista settings.
I don't have an Asus MB or Vista, so I can't go into details of what to look for, you'll have to Google for info about "computer wake up" for your setup

[Bjs]

Disconnecting the psu from motherboard by molex will prevent psu from powering up as there is a feedback sensor wire ... no v detected, no power on.

Fans running and nothing else ... simple... go buy another psu ... and congrats on the last one lasting so long.

[ocgw]

Disconnecting the psu from motherboard by molex will prevent psu from powering up as there is a feedback sensor wire ... no v detected, no power on.

Fans running and nothing else ... simple... go buy another psu ... and congrats on the last one lasting so long.

might be easier to just flip the switch on the back of the psu if it has one

ocgw

peace

[redwudz]

If the computer turns on normally at other times, I would suspect the PS also. But check your BIOS for any kind of 'triggers' that may turn on the computer. That could be from a external USB or a modem or LAN adapter, or a few others. Though since it doesn't go through boot, that points back to the PS again.

I would change it out, and if the problem persists, and if nothing in the BIOS is doing it, then the problem could be the MB. But I doubt that. The PS is still the obvious choice. And I would be very careful if you have the computer plugged in with the 24pin ATX unplugged. While it shouldn't do anything normally, with your problem it could put power to the motherboard through the 4/6 pin CPU power connector and do some damage.

The 24 (Or 20) pin ATX power connector has one pin that is connected to ground by the MB and that turns on the PS. The front panel switch is hooked to the MB at logic levels (Probably 5VDC) and when it's closed, that sends a signal to a switching transistor in the MB that brings the PS 'ON' terminal on the ATX connector to ground level. That signals the PS to turn on.

[mysts]

Thanks redwudz your answers are always informative

I have already ordered a PSU.

Then I got to thinking that since the PSU turns on when the 20 pin connector is plugged in that maybe the motherboard is sending a false signal to the PSU.

[GKar]

A weak bios battery (cr2032 i think) can cause flaky things like that too.

[mysts]

To anyone who is inerested in the conclusion to this thread.

I tried a new PSU. Same problem

I tried a new motherboard. Bingo-that fixed it. I am now back in business. I do thank you for all your suggestions.