"larry moe 'n curly" wrote in message
...


Arfa Daily wrote:

To some extent, I don't think it is all the capacitors' fault, to be
honest.
The places that electrolytics are found in today's equipments, tend to be
very stressful to them, when you couple in other factors such as the
international law on pain of death that requires designers to place
electros
as close as is physically possible to anything that runs hot, and then
to
mount the power supply or whatever board they're on, upside down in the
corner of the equipment with the least airflow, it's actually not that
surprising that these devices exhibit such *apparent* unreliability.

So why do the good brands tolerate those conditions so well while the
same old junk brands don't? And contrary to what you say, most of the
caps aren't in hot spots but are running at under 60 Celcius


So, what exactly are you saying ... ? That better quality components
tolerate abuse more readily than cheapo crap ones ? Very profound ... I
don't think that is actually at odds with anything I said, is it ? I seem to
recall in my original reply to William that part of the reason that he may
have had good luck in regard to electrolytic failure, is the fact that he
has tended in the past to buy better quality equipment where the
manufacturers have been prepared to "design to a better spec with a few
cents more spent on components ..."

As far as your contention that most of the caps that fail are running at
under 60 deg and are not in hotspots, that may be true if you are talking
just mobos, which are a bit of a special case in that apart from all the
problems that have been caused in the past with boards built using caps with
fake electrolyte, the caps that fail are all decouplers on constant DC
rails, and are rated voltage wise pretty close to the continuous voltages
that are applied to them. Even accepting that, many of the decoupling caps
that do fail on mobos, are sited very close (by nature of the job that they
have to do) to LSIs which *do* run very hot.

The caps that I am talking more about in general, are on switch mode power
supplies, where they are subjected to huge stresses from the high frequency
pulse currents that they have to endure, and the self heating caused by this
in all but the most expensive types, very specifically specced for use in
these positions. Further, the ones that fail most regularly are, without
doubt, the ones positioned close to heatsinks. I replace hundreds every year
in the course of my daily work. Although the caps positioned on switchers
are by far the most common ones to fail, they are by no means the only ones.
I also replace many in other circuits, for instance audio output stages,
where failed ones are almost invariably close to heatsinks.



I also suspect that the eco-fanaticism that has given us lead-free solder
doesn't
help either, as the elevated process temperatures required to get this
hateful stuff to stick to anything other than itself, is known to not do
some
components a lot of good,

But the problems with junk capacitors showed up way before the switch
to lead-free solder, and only one of my RoHS mobos has so far popped a
cap, probably more because it's newer (late 2007), not because it's
better, but it has the same OST brand junk caps.


I don't dispute that junk capacitors have been failing for a long time, but
that is for the very good reason that they are ... well ... junk, not to put
too fine a point on it. However, if we take junk out of the equation, anyone
directly involved at the sharp end of electronic service will tell you, as I
do now, that over the last five years or so, the incidence of electrolytic
failure has increased a lot with the increased use of switchmode power
supplies in all sorts of consumer equipment, and the unstoppable rise of
Chinese designed and manufactured equipment, where many good design
practices, such as ensuring adequate ventilation, are not observed on cost
grounds. As to whether the increased process temperatures of lead free
soldering has had any effect on long term reliability of electros, I really
don't know for sure. I could be wrong, but it seems to me that over the last
couple of years, the incidence of electrolytic failure has increased even
more than the trend of the last 5 or 7 years, so it was just a thought in
that this was something else that had changed in that timeframe, and may
have been a contributory factor

The real fault lies with the makers of junk, period.


Some of the fault lies with the makers of junk, agreed. But not all, by any
means.

Arfa