PC smoked and almost caught fire... Causes?

[goldenfleece 11]

A PC I had running and which was only 3 weeks old for some reason suddenly started pouring out smoke from the fan vent at the back....I pulled the mains plug and it continued to smoke so I put the whole case outside and let it smoke, which it did for about 10 minutes. After it had cooled down I opened the metal case to reveal a partially melted motherboard, and the cause seemed to be the power supply unit had let thro raw mains voltage to the board, as the leads from the power unit were all one solid fused plastic burnt lump......

 

For some reason the mains fuse in the plug did not blow, and it was still running when I pulled the mains plug so failed to blow any internal fuse.....

 

Any ideas? Cheap base unit PC brand new so its covered under warranty....nasty cheap power unit had no power switch on back and was rated at 350W.......nothing running on the PC except windows XP, no USB devices and no power draining components.....WHAT HAPPENED?

[D2J 10]

Power surge, loose internal wire, it could have been anything. Never known that happen though, Odd.

[JoeP 11]

That's very unusual - I've had this happen only once when I plugged a machine in that had just been delivered form the US. Unfortunately we'd not checked that the PSU was set to 240V....it was still set for 120V.

 

That was spectacular. Almost gave me heart failure.

[sallonoroff 10]

What was the 'brand' of the PC? And the power supply?

 

Just so people know 'who' to be wary of...

 

 

.

[muddycoffee 10]

That's very unusual - I've had this happen only once when I plugged a machine in that had just been delivered form the US. Unfortunately we'd not checked that the PSU was set to 240V....it was still set for 120V.

That was spectacular. Almost gave me heart failure.

 

That must have been a while ago Joe, all the modern switch mode PSUs have auto selecting supply voltages.

 

Although I have noticed over the last 5 years that they seem less reliable, it could be something to do with the loads the have to supply now.

[tom3t0 10]

A PC I had running and which was only 3 weeks old for some reason suddenly started pouring out smoke from the fan vent at the back....I pulled the mains plug and it continued to smoke so I put the whole case outside and let it smoke, which it did for about 10 minutes. After it had cooled down I opened the metal case to reveal a partially melted motherboard, and the cause seemed to be the power supply unit had let thro raw mains voltage to the board, as the leads from the power unit were all one solid fused plastic burnt lump......

 

For some reason the mains fuse in the plug did not blow, and it was still running when I pulled the mains plug so failed to blow any internal fuse.....

 

Any ideas? Cheap base unit PC brand new so its covered under warranty....nasty cheap power unit had no power switch on back and was rated at 350W.......nothing running on the PC except windows XP, no USB devices and no power draining components.....WHAT HAPPENED?

even the computers are getting ticked off about the smoking ban lol

[muddycoffee 10]

Goldenfleece,

I don't think your PSU would have allowed mains voltage onto the motherboard, I would suspect that a component failed on the motherboard and went short circuit.

The mains fuse didn't go because the mains side was probably pulling less than 3 Amps.

[JoeP 11]

That must have been a while ago Joe, all the modern switch mode PSUs have auto selecting supply voltages.

 

Although I have noticed over the last 5 years that they seem less reliable, it could be something to do with the loads the have to supply now.

 

It was 2000 - I was working for GE Capital in Leeds and we had a batch of PCs sent over from the US. I have to say I expected it to be auto-selecting!

 

There was a loud bang and the smell of exploded eletrolytic capacitors.

 

The amazing thing was that despite the smoke pouring out of teh back of the machine, all I needed to do was replace the PSU and the machine fired up first time.

 

Power supplies HAVE got crappier, I think.

[Johnh 10]

Is this PC a 'home made' one or one commercially available? You don't say what make it is?

[mrmist 10]

You've answered your own question here "nasty cheap power supply". It's probably got a 350W sticker on it, but one problem is that the cheapo supplies can't match what the sticker says, and another is that they fail to supply the right sort of power across the right outputs. It sounds like the PSU overheated sufficiently to cause it to melt (cheaper PSUs don't have the protection circuits that better-quality ones have) and that this heat was sufficient to melt the motherboard too.

[goldenfleece 11]

it was from NOVATECH, mail order computers based in Portsmouth...used them for 12 years and all usually fine

[xafier 10]

That's very unusual - I've had this happen only once when I plugged a machine in that had just been delivered form the US. Unfortunately we'd not checked that the PSU was set to 240V....it was still set for 120V.

 

That was spectacular. Almost gave me heart failure.

 

That's happened to me too, I went into a panic attack almost, it just went with a loud bang that scared the hell out of me! Wasn't fun that's for sure!