PDP 11 gear finally moved

william degnan billdegnan at gmail.com
Wed Jul 22 07:31:55 CDT 2015

This thread has gone on for a while and I think we all get the points
here, but one other consideration - how will removing and replacing a
component damage the board?  Damage the board and it's game over.  One
should always take the overall board's ability to handle replacement.
With the board in mind, I avoid any part replacements and try to keep
them to what is proven necessary only.

On Wed, Jul 22, 2015 at 8:18 AM, tony duell <ard at p850ug1.demon.co.uk> wrote:
>> > 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
> will'.
>> 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)?
> -tony


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