7 Oct
2010
7 Oct
'10
3:37 p.m.
On 7 Oct 2010 at 15:09, Eric Smith wrote:
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.
That picture will most likely change if it hasn't. I recently
revisted a small pile of Boschert switching PSUs from about 1976. A
fair number of them had electrolytics that were little more than
empty cans. No obvious seals blown, just bone dry inside. I believe
they were either Illinois or Elna. The high frequencies used in
these coupled with the relatively poor ESR characteristics of the
capacitors of the time probably means lots of internal heating and
subsequent failure.
--Chuck