You don't know til you try . . .

When PC becomes Pretty Combustible

, posted: 6-Apr-2011 08:44

The client calls saying they had a burning smell and the computer no longer works.

Yeah, I know PSU you say. Not this time.
I could smell it as soon as I walked in the door.
Not the usual blown caps.
Lookie what I found.
First time I have seen anything like it.

Photobucket Photobucket

Anyone care to speculate on the cause?

I took the unit back to the workshop and left it overnight before putting the HDD into a replacement unit.
The whole place stunk in the morning, that thing was still letting off gases a day after the initial smoulder.

It was an old(4 yrs?) IBM Netvista A30 (6826).

The underside

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Comment by CYaBro, on 6-Apr-2011 09:37

Find anything underneath the mainboard?

Author's note by MrWestie, on 6-Apr-2011 09:48

Good point, pulled the board off to have a look, no sign of a rouge screw.
Post updated with image.

Comment by freitasm, on 6-Apr-2011 11:40

Tried looking for a rogue screw, instead of a rouge one?


Comment by michaelt, on 6-Apr-2011 11:46

It could still be the PSU at fault.

Never seen it myself, but some PSU's can fail and send high voltages down the power leads to the motherboard, which in turn can burn the motherboard. 

Comment by Skoyaz, on 6-Apr-2011 12:05

Possibly it was a mosfet failing (little black oblongs with 2 solder points on one side one on the other, looks a bit like a Y)
Apparantly often when they fail they short-circuit, guess if nothing stops them they get hotter untill they burn.
Seen it before but not in a pc.

Comment by sleemanj, on 6-Apr-2011 15:49

Very nearly lost a building (an upstairs sleepout above a garage) to a PC fire a few years back, luckily somebody noticed the acrid smoke pouring out of a window and called the fireys before any major damage done.

Carpet got burnt through, as did a couch which was next to it, and the entire place needed repainting, from memory insurance replaced the bed as well because of the smoke damage.

Basically the entire contents of the case was incinerated.  Don't know what caused it.

Comment by jaymz, on 6-Apr-2011 16:46

What was plugged into the ribbon cable seen in the first pic?

Author's note by MrWestie, on 6-Apr-2011 17:21

Nothing, it is the serial header.

Comment by Elpie, on 7-Apr-2011 03:21

Was it in a building where there's unflued gas heating or coal fires nearby? I've seen a PC that looked a lot like that. The PSU was at fault but what caused the burn was a fine film of gunk that made it in through the window from a neighbouring property that kept a coal fire burning all winter. Both types of heating leave a very fine sticky film in patches inside the case, that is not responsive to normal dusting. This is highly combustable. The smell from the coal-fried PC was horrible. 

Author's note by MrWestie, on 7-Apr-2011 09:19

I have seen that film on some PC I have cleaned. Not in this case though. Tpe pc was located in a showroom, city end of broadway newmarket. It is a tile showroom so every time they update their display there is a lot of fine dust kicked up. I keep telling my clients damp dust can cause the pc to crash, now I can honestly add it can also cause it to bust into flames 

Comment by richrdh18, on 10-Apr-2011 19:11

I've experienced something similar to this, i got called to a job a few years back for someone who reported that there pc stopped working after a lightning strike across the road.  I immediately thought PSU, so went out and replaced it, I replaced the PSU, and had the pc resting on its side with the cover off, i booted up the pc, turned around and was talking to the client, i noticed a burning smell, looked back the pc was in flames.  I pulled the power out and put the fire out.  Afterwards i tested the new PSU and it was fine, so i suspected that somehow something had burnt out or short circuited the mobo.  Had to write the pc off and he replaced it under his insurance.

Comment by Chris Vighagen, on 15-Dec-2012 10:44

Im not sure but tin whiskers could be the culprit here. It's a bit rare but becoming more and more common due to the RoHS act. NASA Has known about this for quite some time and done extensive research on the subject. Basicly the solder alloys that dont use lead have a tendency to grow thin strands that look like cat's whiskers. And they can carry quite a current and blow stuff out. THen again I might be wrong. My first thought was that the FC-2001 was the culprit as itt looked like the side of it had blown out but that's just an oscillator and the side of it hasnt been penetrated. So Im thinking tin whiskers shorting a mosfet.

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