old ceramic capacitors (was Re: Move on, nothing to see here (wasRE: the arrogance of youth [was RE: UNIX V7]))
hilpert at cs.ubc.ca
Fri Jun 12 15:46:08 CDT 2009
Eric Smith wrote:
> I wrote:
> > I don't think ceramics are likely to have gone bad unless
> > they've been subject to extreme mechanical shock.
> dwight elvey wrote:
> > The older ceramics are notorious for going short when used
> > in low current applications. As bypass caps they would self
> > remove the short because of the current. In low current
> > applications they just become vary leaky.
> > Having worked on pinball machines, I've replaced a lot
> > of these bad caps when used in the switch inputs.
> > I've also replaced a few when in the services on radio
> > equipment.
> > I'm told it is related to metal migration.
> I stand corrected! I've never observed that problem previously, but now
> I know another thing to watch out for when restoring old machines. I'll
> have to mention this to the other guys on the PDP-1 team. Maybe this
> might be one of the problems with the notoriously unreliable pulse
> amplifier modules. On the other hand, they were notoriously unreliable
> even when new.
Just to note, micas can suffer from metal migration as well.
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