7 Oct
2010
7 Oct
'10
3:09 p.m.
William Donzelli wrote:
I suspect that most big old electrolytics found in
older computers
mainly die from the seals breaking and moisture getting in, just as
capacitors of the 1940s (even micas) are fond of doing. No amount of
reforming will fix this problem.
I thought that when the seal failed, the electrolyte dried out? Either
way, though, you're correct; once the seal has failed the capacitor
needs to be replaced.
I worked on the PDP-1 Restoration Project at the Computer History Museum
in Mountain View, CA. This equipment was manufactured in 1961. We did
about six months of inspection, maintenance, and repair of the PDP-1 and
the Type 30G display before we first applied power. Part of this
process was to check all of the electrolytic capacitors, and reforming
or replace them as necessary. It appeared that all of the capacitors
were original. Many of them needed to be reformed, and we used an
extremely over-engineered approach to doing that. Only a very small
percentage of the electrolytic capacitors had failed such that they
could not be reformed.
I fully expect that all of those capacitors will fail eventually, but
there isn't nearly enough data to predict a mean lifetime.
Eric