Diagnosing a Bad Power Supply

[tikit0rch]

I have had an issue with my home built computer for the last year or so. The computer will not turn on unless it has been unplugged from the wall or the hard power switch on the back of the PSU is toggled off for a few seconds then back on.

For example, if you shutdown the computer but then try to use the power button on the front of the case it will not respond. Once you unplug the PC from the wall or toggle the hard power switch in the back of the case for five seconds the computer will fire up just fine. Also, the system will not sleep, if it goes to sleep it just dies and will startup as if the plug was pulled. Does this sound like a power supply or possible motherboard issue? It's a home built rig -- Athlon 64 3000+ (OC'd), 1GB DDR RAM, Antec case and power supply, Epox 9NPA+ Ultra NForce4 Ultra motherboard. The system did run properly at one point for at least a year.

Thanks for any help you can provide.

 

[Harvey]

The easiest way to figure it out would be to try another supply on your board and/or your supply on another system.

 

[Puffnstuff]

You aren't telling us anything about your ps apart from that it's made by antec. Put a digital multimeter on the ps rails and see what the voltages are to know for sure.

 

[tikit0rch]

Don't have a multimeter I'm afraid, model number is Antec SP-350 350W power supply 240-pin ATX + 4 pin CPU power lead. The power supply does seem to be making a bit of a "scratching" noise out of the internal fan. The external fan has never turned before but I read somewhere that this was normal behavior?

 

[heymrdj]

Sounds like the PSU has no working +5VSB rail. Just a guess...

 

[Puffnstuff]

You definately need a better ps.

 

[Deanodarlo]

As heymrdj, sounds like the standby +5vsb voltage.

I posted about such an issue here:

http://forums.anandtech.com/me...id=84&threadid=2150996

More and more people are using USB devices when the PC is powered down - keyboards, mice, wireless adapters, cameras, charging satnav's etc, and it ends up killing the +5vsb on some PSU's even if it is rated for the required 2A.

That's what happened to me - I have a perfect PSU except for it's damaged 5vsb, which in effect renders it useless. The next model of that PSU had a "strengthened +5vsb line". Hmmm, I wonder why!

I have since jumpered my motherboard to kill 5vsb voltage to as many external sockets as possible when the PC is powered down. Yes I lose keyboard power on, but I don't want to loose another PSU simply because it's 5vsb line has died.

Of course, this may not be your problem, but it's definitely one to check out as a possibility.