HP 2100A Restoration

Hayden Kroepfl perlpowers at gmail.com
Tue Aug 2 17:54:49 CDT 2016

Well I'm hoping for the memory section that I can find at least one of the
4 core boards that works right away. I've got an 8k driver board I can swap
it so I could run the system on only a single core board if needed. I'd
probably write a short program to do a bunch of memory writes, reads, and
such to exercise it for a few hours or such.

The power supply going bang is one of my worries. I've got an old 80s logic
analyzer with power supply issues, while testing got a big spark by one of
the huge filter caps in it and it put me off working on it for a long while

It would have been quite nice if there was no CTuL logic in the system,
when repairing my Altair if I find a dead logic chip I can still buy modern
compatible replacements. If one of these die, I'd probably have to build a
circuit out of discrete transistors on an ugly protoboard.

On Tue, Aug 2, 2016 at 3:46 PM, Rik Bos <hp-fix at xs4all.nl> wrote:

> > -----Oorspronkelijk bericht-----
> > Van: cctalk [mailto:cctalk-bounces at classiccmp.org] Namens Jay West
> > Verzonden: dinsdag 2 augustus 2016 23:24
> > Aan: 'General Discussion: On-Topic and Off-Topic Posts'
> > Onderwerp: RE: HP 2100A Restoration
> >
> >
> > There is an HP book specifically on I/O interfacing to the 2100 (and
> 21MX) I/O
> > bus. I think there's also an abbreviated chapter on it in a different
> manual. I'll see
> > if I can dig up the name and if it's online anywhere.
> >
> > I've restored at least five 2100's, and run a dual cpu 2100A & 2100S
> system
> > regularly. I have never heard of nor seen a power supply failure on any
> of them.
> > The power supply always came up with little or no pot adjustment, and
> nothing
> > else required. I'd be surprised if your PS needed any attention unless
> they were
> > under water.
> >
> > Debugging the memory section is a far different matter. It's far *far*
> easier to
> > troubleshoot if you have a known working set. If not, it's very easy for
> boards to
> > test ok and then later fail and then later test ok (bad upper section of
> a 16K
> > driver, etc.).
> >
> > J
> About power supply failures mine did have one, when under power after a
> few minutes there was a loud bang and the system resets.
> Which would be repeated every few minutes, some investigating and
> measurement later I discovered one of the high voltage elco's shorted every
> few minutes.
> Which started the power on cycle and resets the cpu.
> After replacing those all voltages were stable and in range and the
> banging was over ;)
> After some testing I concluded there were some faults in the cpu, being
> the lucky owner of an extender board I was able to fix all the errors.
> The HP 2100 service manual and hardware course and engineering reference
> are a big help fixing the 2100 and as J says a set of known good cards can
> be of help too.
> But knowledge of the working of the micro instructions is also a big help,
> IRC the micro instructions are described in both the engineering reference
> and the service manual both can be found on bitsavers.
> The only weak point of the 2100 is the use of uCTL a Fiarchild DTL
> derivate used for IO drivers in the 2100 series.
> Brent Hilpert has a lot of info on his site about those gates.
> -Rik

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