On Mar 21, 2014 3:48 PM, "Tony Duell" <ard at p850ug1.demon.co.uk> wrote:
can somebody please expalin why I rarely see capacitor
failure, for all I
work on machines a lot older than this Osborne?
It depends a lot on the manufacture of the capacitors, and seemingly not
necessarily in ways that strongly correlate with other specific measures of
"quality". I definitely don't understand it. I would expect the rate of
oxide layer breakdown for non-use to be consistent across all aluminum
electrolytic capacitors, but it isn't. My best guess is that the
electrolyte chemistry somehow stabilizes the oxide. Perhaps they use
additives with that specific purpose. Certainly the electrolyte formulation
varies considerably, and often is a trade secret.
After a decade of non-use, some (but not all) of the 40-year-old capacitors
in the PDP-1 had to be reformed, and a few of those could not be reformed.
It is entirely possible that capacitors made more recently may have a
slower rate of non-use oxide breakdown.
Eric