PDP 11 gear finally moved

tony duell ard at p850ug1.demon.co.uk
Wed Jul 22 07:18:29 CDT 2015

> > They reliably do what they're supposed to do.
> You didn't answer the question. How do you know those aluminum
> electrolytic capacitors are functioning just as good as they did when they
> were new? Unless you've tested them out of circuit, you simply cannot make

That, actually, is the wrong question to ask. You should ask 'How do you
know if these old capacitors are working as well as the brand-new replacements

> that assertion.

I think he did answer it. If the unit is operating correctly then the capacitors must be
sufficiently good at that time for that unit.

Now, whether they will go on working is something that is very hard to tell. But that applies
to every other component in the unit. An IC might work find now and suffer bond-out wire
failure later on the same day.

> Just like the NiCd and SLA batteries I mentioned, aluminum electrolytic
> capacitors by their very electrochemical nature degrade as they age and as
> they are used. You cannot claim that a 20-30 year aluminum electrolytic

Semiconductors also degrade both with time and use. I would think a 30-year-old
3 terminal regulator IC was also beyond its design life. So do you replace those 
'anyway'? The damage done if one those fails is likely to greatly exceed the damage
done if a capacitor fails.

Do you replace all EPROMs in case they develop bit-rot (They are most likely way
beyond their design life by now)?


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