PDP 11 gear finally moved

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Jul 23 09:06:48 CDT 2015

    > From: Lyle Bickley 

    > we tested each capacitor for capacitance and ESR
    >  ...
    > Each power supply had to meet it's specifications .. (every test was
    > logged and documented).
    > ...
    > Every year we do a complete DEC specified preventative maintenance on
    > the PDP-1 which includes testing every power supply for voltage,
    > stability and ripple. 

When you tested the caps, did you all write down all the results? (I see you
logged the power supply results, so I'm guessing you all likely did for the
caps too, but you didn't say explicitly.) You all haven't by any chance gone
back and re-measured any of those caps, have you? (Again, standard PM likely
doesn't include measuring individual components - although if you're not
seeing any drift in the results, that's likely a sign that the components
aren't 'evolving'.)

If so, that would be really informative data about the longevity of these
particular electrolytics.

I say "these particular" because I'm starting to suspect that different
electrolytics behave differently - likely because of fine details of internal
construction, chemistry, etc. And it might even be details that the
manufacturers were not aware of.

I am reminded of a story (which I don't have time to chase down, to make sure
I have the details right) from the SR-71, or maybe it was some NASA gear.
Things all of a sudden started to fail in a way they had not before; after a
great deal of investigation, it turned out something really minor had changed
in the water supply to the manufacturing facility (perhaps they had started
doing municipal fluoridation, I think).


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