08 Sep 2003, 20:56, JIM HOLSONBACK (1:123/140), wrote to ALL:

Hi JIM.

 JH> Hello, ALL.
 JH> Got this email from my friend.  I've interim written to him that 
 JH> AFAIK those bulging top caps are likely a sign of impending death, but
 JH> told him I would ask here.  Please advise. And, what does cause those 
 JH> bulging tops?

 JH> Date: Mon, 8 Sep 2003 19:18
 JH> Subject: Re: question
 JH> Jim,
 JH> I was swapping some memory around the boards in my office and 
 JH> found a couple of boards with  bulging capacitors, but they appear to 
 JH> work fine. Am I about ready to have problems with these or will they 
 JH> limp along fine for the indefinite future? What causes the bulging 
 JH> anyway?
 JH> Bob

The bulging caps are caused by age, drying out of the electrolyte, and high
temperature.  Lots of factors enter the picture.  All electrolytics dry out
with age, starting from the assembly line and warehouse storage!

In practical use, caps are being designed to fit into tighter and tighter
spaces, and less margin is being allowed for voltage to achieve smaller
size.  As the electrolyte dries out, the area that generates 'capacitance'
shrinks, in effect overloading the capacitor, and causing more heat.  The
heat crystalizes the electrolyte, and at some point a crystal may grow to
such a size to penetrate the dielectric, then 'bang'.

Most caps have two built-in features to prevent the 'bang', one is a slit
in the rubber base where the leads go through to release overpressure, the
other is the "X" or "|" on the top of the metal can. 
That "X" is a thinned area that is supposed to act like a pop-top
cola can, and split open to reduce internal pressure.  

If the top has bulged, and not yet cracked open, there's a good chance the
bottom has vented some pressure, along with some electrolyte.  That stuff
eats board traces just like a leaky battery.

The 90 or so I've replaced thus far on the Soyo MBs have for the most part
tested as a pure resistance, dead shorted, in a range from .5 to 3 Ohms. 
Several of the boards I've fixed have also needed new PS's, so there is at
least _some_ collateral damage.  

Best bet is REPLACE them as soon as possible!


     Good luck...  M.

--- Msged/386 TE 06 (pre)