Exploding capacitors!!

[maverick77_uk]

Hi there,

I was recently given an aging soc370 P3 computer for messing with. It was missing RAM (PC100) and a HD, so after wacking in some spares I had lying around, I fired it up to see what was what.

Immediately after turning it on, there was an electrical smell, and a pop and spark from the case. After immediately turning off / unplugging, I had a nose at the the MoBo and one of the capacitors had poped.

This was an old computer, so more out of interest than anything else, was this just a case of a bad capacitor, or could a faulty PSU of done this? If a PSU is faulty, could an effect be an exploding capacitor? or are there safety methods installed to stop that happening, and an exploding capacitor is purely down to a bad capacitor? I'm just trying to use this as a learning experience really!

Cheers!

[aidanjt]

Could be both, a cracked capacitor could cause it to short if there was too much gunk in it, by the same measure a cheap ass PSU would probably do it too.

[kidzer]

I think it would just have been a bad cap, I've only ever blown one up by wiring it up the wrong way (even the little ones make a big bang if they go that way!) - if it was like that on the motherboard it would've gone long ago!

Edit: aidanjt is probably more correct than me though

[kalniel]

Sure this wasn't a planned upgrade mate?

[pollaxe]

I had one explode on me last summer - it was entertaining and quite a pop from it. Some techy type who examined the dead mobo said he thought there was a problem with the tracks on the pcb but who knows? It killed my venerable P4 chip as above though, damned good reason to upgrade!

[mycarsavw]

...I had a nose at the the MoBo and one of the capacitors had poped...

[peterb]

If the mobo hadn't been used for a while, then the cap may have deteriorated. To keep costs down the components are used don't have much leeway on the spec. (For example if the voltage that it is to be used at is 5V, then 5V devices will be used, rather than a slightly more expensive (say) 10 V device). Electrlytic capacitors are voltage sensitive - over-running one by just a little bit will cause premature failure, so if the PSU was pumping out just a a bit to much, that could also have an effect.

In this case I would think it was just the age, and the fact that it hadn't been used for a while - and you were unlucky!

[DougMcDonald]

If a PSU is faulty, could an effect be an exploding capacitor? or are there safety methods installed to stop that happening, and an exploding capacitor is purely down to a bad capacitor?

I was under the impression that the popping capacitor itself was a safety feature! Same theory as a fuse blowing etc

[aidanjt]

I was under the impression that the popping capacitor itself was a safety feature! Same theory as a fuse blowing etc

Naw, the job of the capacitor is to 'buffer' electrical charge, so if there's a slight voltage droop (which is natural) the IC it's connected to wont produce random errors.

[DougMcDonald]

Yeah, but if the top blows the capacitor will not distribute it's charge (as far as i'm aware), therefore protecting any component further down the line.

[aidanjt]

It depends, a cap overload could blast charge out the negative pin if it goes in a certain way, they don't make a good replacement for fuses/breakers, generally PCBs aren't intended to be serviceable anyway.

[DougMcDonald]

I'm certainly not suggesting that they would be a replacement for a breaker/fuse, as obviously they have a distinct purpose, more than it has an element of being able to kill itself, rather than other components down the line.

Good point though as largely mobos are not intended to be user serviceable. Although i would expect an electronics expert to be able to replace the capacitor and re-use the mobo if necessary.

[aidanjt]

Yeah, a resolder job is probably doable with a skilled hand, not many would bother though, I suspect.

[peterb]

Yeah, but if the top blows the capacitor will not distribute it's charge (as far as i'm aware), therefore protecting any component further down the line.

No! The capacitor blows because it overheats - either as a result of passing too much current (if the ac ripple on the DC supply is too high) or because the dielectric is punctured because the applied voltage is too high, and causes a short circuit internally, which causes a large DC current to flow. Either way, it is an unintended failure mode, and nothing to do with distributing charge! All it does is distribute electrolyte over the surrounding components!

[Andy3536]

Normally dielectric is faulty or degraded.
Might be worth giving a try though, you could probobly pick one up for less than a pound!
I have done electronics servicing for a while and although most modern boards are a right pain to work on still perfectly feasable.
All you have to be aware of is that the tracking and especially the plated through holes come away from the board very easy.
If you have any experience de-soldering it would be worth giving it a try, whats the worst that could happen, you'll waist a £1 and 30mins?

[maverick77_uk]

Hi all,

Thanks for all your suggestions! To be honest, think I'll just let it go to the great MoBo in the sky - although I'm fine with plugging a computer together, finer soldering electronics is not my forte! Probably end up blowing myself up if I tried!

LOL Mycarsavw! I'll learn to spell one day!

Looking at the PSU, I don't think it was exactly a "quality component", so may of been the cause.

Oh well.....Another day, another blown computer

Kalniel - you know me, can never pass up a tinker with computers from yester-year!