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Replacing motherboard capacitors

Just tried powering up an old (386) PC, and was greeted with an acrid
smell and a puff of smoke; one of the motherboard capacitors had blown.
I'd like to try replacing it, but my main concern is: what rating
should I buy as a replacement? The surviving originals are all marked
"10+ 16J".
 
C

Charles Schuler

Jan 1, 1970
0
Just tried powering up an old (386) PC, and was greeted with an acrid
smell and a puff of smoke; one of the motherboard capacitors had blown.
I'd like to try replacing it, but my main concern is: what rating
should I buy as a replacement? The surviving originals are all marked
"10+ 16J".

10 microfarads @ 16 volts (just a guess).
 
I

inty's world

Jan 1, 1970
0
they are tantalium caps, replace with another tantalium.
 
D

Dave D

Jan 1, 1970
0
inty's world said:
they are tantalium caps, replace with another tantalium.

I'd replace them with electrolytics unless there's very good reason why
tants are essential. As they smoked I'd assume they're across the supply, ie
filter caps, so as long as they physically fit, electrolytics are a
reasonable choice for replacement.

Tantalum caps have very high failure rates, and worse still they often fail
short circuit. I never use them unless I have to.

Dave
 
I

I.F.

Jan 1, 1970
0
Just tried powering up an old (386) PC, and was greeted with an acrid
smell and a puff of smoke; one of the motherboard capacitors had blown.
I'd like to try replacing it, but my main concern is: what rating
should I buy as a replacement? The surviving originals are all marked
"10+ 16J".

The last PC I had do that - the PSU regulation had failed!
 
A

Andy Cuffe

Jan 1, 1970
0
Just tried powering up an old (386) PC, and was greeted with an acrid
smell and a puff of smoke; one of the motherboard capacitors had blown.
I'd like to try replacing it, but my main concern is: what rating
should I buy as a replacement? The surviving originals are all marked
"10+ 16J".


That's a 10 uF 16 volt tantalum cap. They tend to be very reliable,
but when they do fail, they short and smoke. A tantalum cap would be
best, but any decent 10 uF 16 v cap should work in that application.

There's no need to replace any other caps if only one failed. This
isn't like the more recent motherboard that were made with dozens of
defective caps.

As a quick test, you can try removing the cap. Chances are the PC
will at least POST without it.

When you replace it, note that the stripe on a tantalum cap identifies
the positive side, but most other caps have the stripe on the negative
side.
Andy Cuffe

[email protected]
 
Many thanks to everyone who's replied in this thread.

Andy said:
As a quick test, you can try removing the cap. Chances are the PC
will at least POST without it.

I did this (using a known good power supply) with mixed results. It
looks as if the -12v line is shorted to ground somewhere, because the
power supply refuses to switch on if it's connected. If I disconnect
-12v and leave the other power lines connected, the board powers up and
makes it through POST.

I think I'll let the matter rest, at least for now.
 
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