HP 2100A Restoration

Hayden Kroepfl perlpowers at gmail.com
Tue Aug 2 16:09:51 CDT 2016

Alright, thanks for all the helpful tips and information.

I guess what I'll do when disassembling it is note down every electrolytic,
and probably just throw them all into a Digikey order that I'm working on
for other repairs.

Probably will give reforming a try if it seems practical, but I assume on
the power supply that's going to mean desoldering one leg on each cap. At
that point it's probably better to just replace the cap. My only worry
would be obsolete/oddball cap values that I'd have to inspect the circuit
to see what replacement I can use, eg. 290uF and 250uF caps.

On another note, has anyone ever tried making their own I/O boards for any
of the 2100 series computers? The closest I found was
http://newton.freehostia.com/hp/ where he makes a paper tape emulator and
disk interface. However both of those are designed to connect to an
existing I/O board like the "microcircuit interface". I haven't seen
anything yet on how to interface to the I/O bus, but then again there are
thousands of pages of manuals still to browse through.

On Tue, Aug 2, 2016 at 10:42 AM, Glen Slick <glen.slick at gmail.com> wrote:

> On Mon, Aug 1, 2016 at 10:25 PM, Lyle Bickley <lbickley at bickleywest.com>
> wrote:
> > On Mon, 1 Aug 2016 22:11:17 -0700
> > Bob Rosenbloom <bobalan at sbcglobal.net> wrote:
> >
> > --snip--
> >
> >> There's a bunch of small electrolytic capacitors on the Inhibit
> >> Driver Load Card, A106, that needed to be reformed before my memory
> >> would work reliably.
> >
> >> They reformed themselves in one of my units. I had memory errors for
> >> an hour or so then they went away. On other units, I reformed the
> >> caps (took the board
> >
> >> out and slowly brought it up on a bench supply), and had no memory
> >> errors at first power up of the system.
> >>
> >> Bob
> >
> > I had exactly the same problem with the capacitors on a spare Inhibit
> > Driver Load Card. Most would not reform so I just replaced them with
> > modern caps. The board (and memory) worked perfectly after that.
> >
> > Lyle
> That is good information to know. I have a 2100A that I haven't
> touched in a while. It had memory issues that I never got around to
> trying to debug. Next time I work on it I'll look at the IDL card.

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