On Fri, 17 Jul 2015, tony duell wrote:
Perhaps. But not all of it, certainly. I'm currently four for four
fixing dead flatscreens by re-capping their power supplies; I imagine
others have similar experiences. It's not a huge stretch to imagine
This could be taken to show that modern capacitors are not reliable, and
given that there are plenty of 40-year-old ones still in use in various
classic computers here it would be better to leave them as-is
It really depends. If I'm having to replace filter capacitors in a faulty
PSU or monitor, even if I've isolated the problem to one or two
capacitors, I would be a fool not to replace them all because the next
part that fails will be one of those which I didn't replace (been there,
done that, own the tee shirt). A standard 85C or 65C rated 20-30 year old
aluminum electrolytic is simply past its useful service life.
More seriously, a lot of modern consumer stuff seems to have
marginally-rated capacitors (and the use of 85 degree ones doesn't
help). Possibly on those it is a good idea to replace them. But the ones
in PDP11s were good quality at the start and were over-spec'd in
general.
With modern electronics, there are high quality parts and there are really
cheap parts. Even though the high quality parts are about the same price
as the really cheap parts when purchased in small quantity (in the one-off
to a few 1000 quantity), profit-driven consumer electronics manufacturers
are still going to use the cheaper parts when they can save even $0.01 or
$0.005 per component or even a few cents on the overall cost of the
complete widget.
Many of these manufacturers also design their widgets to last for the
warranty term and no more. If the consumer gets 2-3 years or more out of
said widget, those manufacturers consider it a loss in terms of potential
profits. In these cases, wholesale replacement of really cheap capacitors
with high quality versions from top tier manufacturers (Panasonic,
Nichicon, Rubycon, etc) can be a /really/ good idea. That said, even the
top-tier capacitor manufacturers have lower end lines of parts, so it pays
to do your homework and choose a longer life (usually lower ESR, meaning
less internal heating and thus longer service life) part when sourcing
replacements.
Even vintage Mallory and Sprague parts are not without their faults. I
recently replaced a bunch of early 1980s era Mallory capacitors which
tested good, but when desoldered from the board, had brown crusty stuff
around the safety vent in their bottom rubber seals. They might have
continued to work "ok" for another year or even 10 years, but the high
quality replacement parts I put in will be good for at least another 20-30
years. (The replacement parts also worked better as the DC rails had lower
ripple after they were installed).
that other power supplies may have similar issues; even if it turns out
to not be the case, there is probably at least a little "can't hurt
anything, right?" running around.
Ah but it can hurt. Damage to the PCB (unlikely, sure), the new part
might be faulty and thus introduce more faults, you might make an error
fitting it, and so on. I prefer to only replace that which needs
replacing.
It really is a case by case basis, however in PSUs, CRT monitors, and
similar where the components are exposed to higher temperatures, it really
makes sense to replace 20-30 year old aluminum electrolytics wholesale.
I guess another way to look at it is that an electronic device might still
be functioning with old aluminum electrolytic capacitors, but is it still
functioning as good as it was when it was new? A vintage device might have
used really high quality aluminum electrolytics when it was made, but even
high quality parts have a finite service life. What you have to decide is
where to draw the when considering wholesale replacement of aluminum
electrolytics, which with vintage electronics, I've found tends to be
somewhere around the 20-30 year point.
