Winfield said:
It's been going around for several years now - cheap non-OSCON
high-density caps with inferior substitute organic electrolytes.
One doesn't always see a bulge; often the most reliable symptom
is CPU crashes. It's generally taken that the fix is a new mobo.
I've been fighting that problem for years. For a time, I was
replacing ALL the caps on motheboards. I have a Pace desoldering
station so that was fairly easy. Some motherboards have fairly sloppy
hole clearance for the capacitor leads, so removal and replacement
were easy. Others (i.e. Dell) looked like the caps were pounded into
the motherboard. If I ripped out the plated through hole along with
the capacitor, it usually indicated that I just destroyed the board.
The first indication of trouble is usually the rubber plug on the
bottom of the capacitor trying to wiggle out of the can. If the board
has a number of lopsided caps, it's either the worlds sloppiest board
manufacturer, or the caps are about to go bad. Usually the rubber
plug shows before the top or sides bulge.
I've tried various methods of detecting bad caps. Bulges aren't
always a good indication. I have an old Dick Smith capacitor ESR
tester, which is easily fooled by the large number of parallel
capacitors. It works fine if the capacitor is independent or pulled,
but not on the motherboard power supply bus.
I've also tried far IR imagers. Nothing like $20,000 worth of
borrowed hardware to repair a $100 motherboard. Some digital cameras
can see near IR and don't work for seeing heat. That has found some
overheated capacitors, but more often just shows the reflected
radiation from the CPU. A finger test of the capacitors is sometimes
effective. If the cap is warm, it's bad.
I've tried to use a scope to detect the expected noise on the power
supply lines, with little success. All motherboards have some noise
on these lines. The point of measurement (and grounding) have a huge
effect on this noise level. Making an accurate determination is
difficult.
The degree of failure is also somewhat entertaining. I've seen
motherboards with severely bulged caps, that continue to function
without incident for many months. Eventually, there's a failure, but
the amount of damage these can tolerate are amazing. On the other
foot, I've seen boards with only a barely visible amount of bluging,
generate boot problems and crashes. I suspect that this is an
indication of board quality.
For motherboards that I just wanted to work, and didn't care what they
looked like, I just chomped off the capacitors with a pair of very
large cutters, leaving the leads in the mother board. I then tack
soldered the replacement capacitors leaving about 1/4" of leads
exposed. It looks truely unprofessional, but gets the job done
without destroying the motherboard. I've also substituted tantalum
caps for the low-ESR electrolytics. Although more expensive, the low
frequency ESR is less, so fewer caps can be used. Please don't tell
anyone I suggested doing all this.
Drivel: See comments on tantalum ESR at:
<
http://ludens.cl/Electron/esr/esr.html>
in the "using the meter" section. I've seen the same problem with the
same caps. If you think we have problems with low-ESR electrolytics,
get ready for more of the same with tantalums.
In retrospect, it's not worth fixing the motherboard. It's just too
much labour. If it's under warranty, get a replacement. If not, buy
a replacement and install it yourself.
Incidentally, I've seen some random CPU's fail along with the
motherboard when run with volcanic capacitors. I haven't investigated
the connection, but I suspect that non-optimum power supply voltages
and substantial voltage spikes, might not be very good for CPU
survival. In general, the ones that crash while booting or running
will have this problem.
