Strange Power Spply problem

[Dodge7]

A few weeks ago, I was working on my computer when I heard a loud pop or bang sound and the screen goes blank. Checkiing the computer, I see no indication of power and all, no LEDs lit, etc. So, I thought the power spply blew.

This evening I replaced the old power spply with another one I had, that I had every reason to believe was good. Other than having a time getting old one disconnected from the motherboard [I had to cut the tab to get it loose] everything seemed to go OK.

Then I truned the computer on = nothing happened, no sign of power at all, just like the first power spply. So I checked the first power spply with a voltmeter, there WAS power on the power lines to the CD drives, HD, ect. Yet they wouldn't open.

This has got me confused? Apparently, the last power spply worked. And the new one should have - yet the computer shows no sign of power. Could the issue be with the motherboard? How could I tell?

[Im New]

hmm tricky my only thought would b a short or sumthing

[Dodge7]

Yeah, I thought it might be a short on the motherboard.

Or, maybe if the motherboard doesn't get power, nother else will work at all?

[Im New]

Originally Posted by Dodge7 Yeah, I thought it might be a short on the motherboard. Or, maybe if the motherboard doesn't get power, nother else will work at all?

i would think it would get power still.....but it would b hard to tell if they had power or not if u couldnt try to say open the disk drive....but my guess its sumthing worng with the mobo....unfortunatly

[Jimmy0]

Try an out of case build to see if anything changes: http://forum.pcmech.com/showthread.php?t=168456

[Cricket]

What brand was the original power supply?

Cheap low quality power supplies rarely have over-voltage protection and the original power supply may have sent a big surge to the computer when it died and that could have fried a few parts including the motherboard.

Cricket

[edfair]

The ATX supply has a standby power circuit that powers the standby seciton of the M/B. The power switch on the case activates the standby section to send a powerup signal to the power supply to give the run power to the M/B.
You can have porblems with any of these and end up with these symptoms.
You can check for the standby power and the standby section of the M/B by checking for voltage on the power up cable on the power supply. Think it is pin 19 and green wire should go to +5 w/respect to one of the blacks. Try a google search for "atx power connector" for the pin layout.
The pop can be any number of things in the power supply or on the M/B. And if it was the power supply it is quite possible that a failure there took out the M/B also.

[Dodge7]

The orignal was an ALLIED 300W. When I took it out I opened it, and looked around inside, there was no obvious damage, the fuse is also intact. The motherboard looks find also.

I checked for voltage on the old spply, and found one with of the whites ... white wires with yellow had power..and so did most of the connectors for CD drives... yet when I checked again, there was no power. So maybe I have two bad power spplys? I think I am going to just have to get a known working power spply and see if that is the issue.

Still, could the motherboard be telling everything to "turn off"? I wonder if there could be an issues with the on/off switch? Or control on the motehrboard?

[flanzig1]

Allied PSUs are known for going bad and usually take out the mother board.

[Dodge7]

Arrrgh... thanks for letting me know though. Losing the PS and motherboard would explain this...

[Dodge7]

Since I wasn't sure my replacement power unit was good, I took my computer to a guy I know who runs a computer repair shop. He said a new power spply that he installed seemed to fix the computer, but wanted to run diagnostics on the motherboard? He thought there could be a problem there.

Shouldn't he just be able to tell by tuning the computer on and seeing if it works?

[glc]

It's not always that simple.

[Powertrip]

Nah Dodge, I wish it was that simple.

He likly wants to run memory and CPU Tests it's worth an hour of labor to know that there are no new problems from this issue, believe me. I fire almost every computer that comes through my shop on a memtest+86 just incase. Hell put it through it's numbers and make sure it's not freezing or corrupting info. Then it will be ok to put back in service, if not you could suffer all kinds of problems.

Also a good idea is to mark failed components or throw them out, if your brain is like mine it gets easially confused. If a power supply works It get's a "Known Good" wrote on it around here lol.

[Dodge7]

PowerTrip

Good idea, I knew I had two power units around, but couldn't remember which was which once I started to think of it... I should have at least tested one before putting it in the computer.

The good news, the motherboard and all tests good. He is just waiting for the new power sppys to get in that he had on order, shipping delays due to the Denver situation and such.

At least I don't need a new computer after all.

[amdjeff]

It probably took out your motherboard. I just had 2 psu's go less than a month apart.

[Dodge7]

Acutually it didn't. I took it to a small repair shop, he ran a diagnosis program, the motherbaord was fine.

I got a new power unit, and it is fine.

I have never been able to find the problem with the old PSU, not obviously damage. I did find a dead insect, I think it migth of been the cause.