PDP 11 gear finally moved

[Robert Jarratt]

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony
duell
> Sent: 17 July 2015 19:56
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: RE: PDP 11 gear finally moved
> 
> >
> > Perhaps.  But not all of it, certainly.  I'm currently four for four
> > fixing dead flatscreens by re-capping their power supplies; I imagine
> > others have similar experiences.  It's not a huge stretch to imagine
> 
> This could be taken to show that modern capacitors are not reliable, and
given
> that there are plenty of 40-year-old ones still in use in various classic
> computers here it would be better to leave them as-is
> 
> More seriously, a lot of modern consumer stuff seems to have
marginally-rated
> capacitors (and the use of 85 degree ones doesn't help). Possibly on those
it is a
> good idea to replace them. But the ones in PDP11s were good quality at the
> start and were over-spec'd in general.
> 
> > that other power supplies may have similar issues; even if it turns
> > out to not be the case, there is probably at least a little "can't
> > hurt anything, right?" running around.
> 
> Ah but it can hurt. Damage to the PCB (unlikely, sure), the new part might
be
> faulty and thus introduce more faults, you might make an error fitting it,
and so
> on. I prefer to only replace that which needs replacing.
> 
> -tony
> =

When I repaired my VT100s I had to replace all the electrolytic caps on the
monitor control board to cure the screen wobble. Before doing so I had
reformed them all and I had tested them all for ESR and they had all tested
fine so I was unable to determine which of them was the bad one. Perhaps
there is other more professional test equipment I could use that would have
helped, I don't know. I did keep all the original caps though (somewhere).

Regards

Rob