Question Burned out 5V lines on power supply- what's at fault? and can it be repaired?

[skewered2010]

Hi everyone!
I had been running an old Antec PP-303X 300W PSU for a number of years, having to replace its original fan, and now 3 years later the 5-volt lines burned and melted, all 4 of them, leaving the ATX molex connector stuck to the motherboard's header. I assume that 4 lines service different devices, so that would imply rather than a bad device (or a device drawing too much current) that it was the power supply that failed. I suppose it could have been the after-market fan that wasn't keeping it cool enough but nothing in the power supply shows any signs of wear or tear.
So: I'm here to ask if anyone has any ideas on what was at fault, and whether the power supply can be repaired (and where).
the following devices installed:
3 IDE hard drives
2 CDROMs
zip drive, floppy (yeah, 90's tech)
Soundblaster live card
SCSI card, ethernet, firewire card, graphics card, and ATI TV tuner card.
Only 2 USB ports that were never used heavily.
4 box fans for the case.
And it looks like it might have toasted some of my RAM, if that helps diagnose.
Thanks!
SK

 

[USAFRet]

and whether the power supply can be repaired

No.

Replace.
Along with anything else that got cooked

 

[--SID--]

Why do you want to revive an over 20 year old PSU that was obsolete 15 years ago? It's not worth it with such an old unit.

 

[skewered2010]

Alright, thanks!
So that leaves the question of what happened.
In particular, can I trust the motherboard again AND/OR the devices/cards I have plugged in?

Right now I'm running a new motherboard, and am plugging each device back in, but I'm hoping somebody can advise on whether a failure of this type tends to come from the power supply or from the device side?

Thanks again!

(and a side question: Can dust cause a short-circuit/current-draw?)

 

[Grobe]

leaving the ATX molex connector stuck to the motherboard's header.

In particular, can I trust the motherboard again AND/OR the devices/cards I have plugged in?

You've pretty much answered your own question. No way should you trust any devices that was connected during that incident. There seems to be a shortcut in at least one of the components.

 

[skewered2010]

Does that include harddrives?

 

[USAFRet]

Does that include harddrives?

Yes.

Everything is suspect until proven good, in a fully working system.

 

[skewered2010]

So let me ask:
if the hard drives are powered off the 4-pin molex connectors, how would they be able to influence the 5-volt lines going to the 20-pin motherboard?

and maybe this is a good place to also ask:
what does it mean when a hard drive isn't spinning up right away with power-on, but sometimes (not all the time) makes a sound ("ghee-ghee") like it's trying to get started, and then finally does.

Thanks for further thoughts on this!

SK

 

[Grobe]

if the hard drives are powered off the 4-pin molex connectors, how would they be able to influence the 5-volt lines going to the 20-pin motherboard?

Because old/cheap PSU are often equipped with only one voltage regulator for all outputs.

 

[Ralston18]

"Influence": All that would take is a short somewhere.....

FYI:

https://www.lifewire.com/molex-4-pin-peripheral-power-connector-pinout-2624582

 

[skewered2010]

Thanks for that link and the thought on voltage regulator.
I have some new info:
I tested the power supply in standalone mode and it is outputting 5 volts just fine on each of the 4 pins. So the PSU appears to be fine, and that would imply the problem is on the computer side.

But rather than a short in one single component, is it possible that I've just had the PSU overloaded all these years and many components were forcing a current draw just a little bit over spec, such that over many years it adds up?

As it stands I have replaced all devices (cards and HD) except for 3, and seems to be running fine. But I also did switch out motherboards. So I'm taking it step-by-step and will report back, but just wanted to know if there were any thoughts on that.

Thanks!
SK

 

[Eximo]

PSUs can't really be tested with open circuit voltages. Only a practical load will reveal if they are functioning and you need an oscilloscope to be sure to any degree of confidence.

Internal shorts happen in components. Could be any of them, including the motherboard you replaced.