"David Nebenzahl" wrote in message
.com...
There's a lot of discussion here about the quality and longevity of
electrolytic capacitors, and to read much of it, one would think that
these are the most failure-prone of all electronic components, and that
any piece of equipment you may have around the house (or lab) that uses
them is likely to fail any day now.

I can't really dispute any of this, except to say that this is not my
experience at all.

Three pieces of electronic equipment I use every day: my computer
(motherboard is about 10 years old), my "good" audio equipment (Technics
amplifier, Vector Research tuner, both somewhere between 15-20 years old),
and the receiver I use for sound on my computer (an Allied that I bought
*used* in 1975).

I have other old elecronic stuff that also works fine.

None of these have had any electrolytics fail, so far as I know. So what
gives? Am I just lucky? Did the manufacturers use higher-quality caps than
what's commonly used today? (The motherboard ain't anything special--it's
an Asus, I think, but I do have extra fans in the enclosure.)


--
Found--the gene that causes belief in genetic determinism

It's not a case of being lucky, for the most part. It's more a case of the
equipment that you're talking about, being old. Electrolytics which fail in
modern equipment, are almost always in switch mode power supplies, or are
post-psu decouplers. The ones that are actually employed in the psu itself,
are under enormous stresses from the high frequencies that they have to deal
with, and it is essential that in order to minimise failure through self
heating, only top quality low ESR high temperature types are used.
Unfortunately, such caps impose an increased financial burden on the design,
so even if the designer had good intentions when he specced them, the bean
counters are likely to demand a cheaper lower specced type is used in the
production version.

Add to this that much equipment now is very small, and the caps in question
will be further stressed by being specced for the smallest physical size
that will do the job, and that often means that the voltage rating will be
only a couple of volts above the actual voltage that they have to work at.
Now I know that there have been those on here in the past, who have got
really worked up about this, saying that if a cap is rated at 10v, then it
should work at 10v applied, for ever, without complaint. Maybe. On paper.
But any of us who are in the repair business, will tell you that in real
life, it just ain't so ...

The old equipment which you have, and which you and others in the thread say
has never suffered any electrolytic problems, is not exhibiting anything
special. 20 years ago, electrolytics were physically bigger for any given
value / voltage rating, so had a bigger surface area to dissipate any heat
from. As the equipment was larger in the first place, there was no
requirement to compromise on voltage rating to get a cap that would fit in
there. The larger internal size also allowed for better air circulation, and
a lower overall internal working temperature. Switch mode power supplies
were a dim idea for the future, so the caps did not suffer high frequency
stress, either.

All of that said, Panasonic / Technics gear suffered for many years with the
little purple 10uF decouplers going short circuit, and you would be
surprised how many cathode bypass electrolytics in valve (tube) amps, are
virtually open circuit, if you take the trouble to check them, and how much
it improves the performance, when they are replaced ...

So, in conclusion, I would definitely say that in my daily repair
experience, electrolytics are now by far and away, the commonest component
to fail, and this, IMHO, is for all of the reasons that I have stated.

Arfa