Fans spin but no other life

[carterbequest]

I got that frightening smell and puff of smoke from my newly rebuilt pc (new Mobo, CPU, PSU) this morning while I was in the process of reinstalling XP. Now the only sign of life I get when I switch it on are the fans (power supply, heatsink, case). The HDDs and CDs are all dead.

Any idea which part(s) are fried? As the HDDs and CDs don't stir I presume it's the PSU but then why would the fans turn?

 

[Reynod]

Interesting point but remember your PSU has + and - 5 volts and + and - 12 volts.

Sometimes only one of the regulators on the PSU goes.

Try another psu first.

 

[jsc]

Any idea which part(s) are fried? As the HDDs and CDs don't stir I presume it's the PSU but then why would the fans turn?

No way of telling how many dead parts that you have without testing. And the fans still turn because the PSU can still produce a little power.

And keep in mind that the puff of smoke you saw might not have been from the PSU. Something on the motherboard may have died.

The following is cut and pasted from one of my previous threads:

Try to verify (as well as you can) that the PSU works. If you have a multimeter, you can do a rough checkout of a PSU using the "paper clip trick". You plug the bare PSU into the wall. Insert a paper clip into the green wire pin and one of the black wire pins beside it. That's how the case power switch works. It applies a ground to the green wire. Turn on the PSU and the fan should spin up. If it doesn't, the PSU is dead.

If you have a multimeter, you can check all the outputs. Yellow wires should be 12 volts, red 5 volts, orange 3.3 volts, blue wire -12 volts, purple wire is the 5 volt standby. Current PSU specs do not require a -5 volt line, but if you have one, it will be the white wire.

The gray wire is really important. It sends a control signal called something like "PowerOK" from the PSU to the motherboard. It should go from 0 volts to about 5 volts within a half second of pressing the case power switch. If you do not have this signal, your computer will not boot. The tolerances should be +/- 5%. If not, the PSU is bad.

Unfortunately (yes, there's a "gotcha"), passing all the above does not mean that the PSU is good. It's not being tested under any kind of load. But if the fan doesn't turn on, the PSU is dead.

 

[carterbequest]

Thanks. I've now tested all the outputs from the PSU using a multimeter and they are all OK. I realise that this wasn't done under any load but it would seem to suggest that the PSU is OK and the motherboard is the problem. Would you agree?

 

[Reynod]

Did you connect the 4 pin power to the mobo?

It comes from the PSU (aside from the 20/24 pin PSU to mobo power.

 

[carterbequest]

Yes, 4 pin connected to mobo.

 

[Reynod]

Um try a loaner PSU just to be sure but it sounds like a mobo funeral might be in order ...

 

[carterbequest]

Cheers all, I've tested everything and it was definitely a fried mobo. I've got a new one installed now and everything working fine.