D Yuniskis wrote:
Hi,

[Apologies if this appears as a repost -- it hasn't
shown up on my server in the better part of a day]

I've been repairing lots of "defective" LCD monitors
for a local non-profit. Of course, many boil down to
bad electrolytics from those notorious Taiwanese
manufacturers.

[I'd like to avoid rehashing that subject as I am sure
there's nothing *new* that anyone can add -- and, it's
not the nature of my question, here!]

What I would like to know is which circuit topologies
tend to aggravate this problem. From my casual
observations (I've done most of my repairs without
the benefit of any design documentation), the failing
components either seem to be proximate to heat sources
*or* in configurations where they see high ripple
currents (suggesting this is a problem with the
devices' ESR -- internal heating).

My observations come from a few *hundred* samples
from different manufacturers, different models,
different subassembly manufacturers, etc.

Does anyone have any *definitive* answers about this?
And, long-term remedies? (i.e., does replacement with
a good, high temp, low ESR cap *solve* the problem or
just kick it down the road?)

Are there lessons to be learned when *designing* these
types of circuit topologies to avoid these failure
modes? (besides picking good vendors)

I can only offer a rumor about a manufacturer of electrolytic
capacitors. The story goes, a major well-known corporation was
developing a physically smaller, less expensive capacitor. They had a
prototype, which design was stolen and began appearing in the
cheap-parts market. The prototype was flawed, so the cheap parts are
similarly flawed.

As an aside to this tale, I can positively say the surface-mount
electrolytic capacitors used in a series of Panasonic DVC Pro video
recorders have an extraordinarily high failure rate.

Shops have opened up specializing in capacitor replacement for those
machines. A complete re-cap can go for $3,000 US.

You would probably have the best results replacing defective caps with,
as you say, better quality ones from reputable vendors.

The following borders upon superstition, but I'll include it:
If you have to choose between two electrolytic capacitors of the same
ratings, and both will fit the application despite one being physically
larger... I'd suggest buying the larger one. It will at least have more
heat-dissipation capacity.