On Sun, 22 Nov 2009 17:26:02 -0000, "Arfa Daily"
wrote:

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,

Generally true. This is old (2005) but the best I could find:
http://www.bigbruin.com/reviews05/nf4thermals/index.php?file=1
6 pages. The hottest they found was 70C and that was in an odd corner
of the MB for no obvious reason.

More of the same:
http://www.bigbruin.com/reviews/thermalimages/
However, these show some chips getting up to 99C. Ouch.

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.

Worse. The caps are not on constant DC. There are huge ripple
currents going through these caps at they heroically try to filter the
DC voltage. You wouldn't need low-ESR caps were it not for the
heating caused by the internal resistance and this ripple current.
It's even worse in power supplies.

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.

Yeah, but along with the general decrease in quality, there has been
proportional decrease in price. It's price that driving the decline
in quality. Running the operating temperature and voltages near the
point of failure is one way to save on costs.

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

Good point. I have no idea if there is a correlation but it seems
worthy of investigation.

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.

They wouldn't make junk if consumers didn't demand low prices. There
are usually "premium" versions of almost any consumer product, but few
can afford the price. (If you want quality, be prepared to pay for
it). Personally, I prefer to blame the government for literally
everything, but maybe not this time.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558