HP 1000 A900 ("Magic") Questions

Glen Slick glen.slick at gmail.com
Fri May 10 12:33:41 CDT 2019

On Fri, May 10, 2019 at 4:14 AM Paul Birkel via cctech
<cctech at classiccmp.org> wrote:
> Aficionados;
> I'm interested in acquiring an HP1000 A900, in any form-factor.
> (http://www.hpmuseum.net/display_item.php?hw=594)
> Basic need would be a chassis/backplane/PS and minimal set of
> CPU/memory/HPIB-controller/terminal-IO PCA, however I'd be interested in
> simply acquiring a PCA-set and I'll work the chassis/backplane/PS
> separately.  Even single PCAs would give me a helpful push forwards.
> And I need to stick to my hobby (beer") budget.
> I'm located in Maryland, USA, and pretty sure that the cost of overseas
> shipping would be ghastly for a chassis.  But maybe not as bad for the tower
> configuration as for the rack-mount.
> If I understand correctly, the CPU consists of:
> 12201A A900 Sequencer Card
> 12202A A900 Data Path Card
> 12203A A900 Cache Controller
> 12204A A900 Memory Controller
> 12220A 768KB RAM  (Or I presume 12103D 1MB, 12221A 3 MB, or 12221B 8 MB.)
> I imagine that I'll need to synthesize my own OTT "frontplane" for the
> memory.
> 12009A HP-IB Controller
> 12040D Asynchronous Multiplexer interface board

The hard part is the A900 chassis/backplane/PS.  Jesse / Cypress
Technology has some 2139A 20-slot listed on eBay, but definitely not
at hobby budget prices. No idea how much room he has for "Make Offer".
I have rarely seen the A900 chassis come up for sale on eBay.

Another hard part is the 12222 memory frontplane. Maybe it wouldn't be
too hard to build an equivalent PCB if the proper connectors can be
acquired. They are 3-row 96-pin connectors. Maybe common DIN 41612
connectors would work, I haven't looked at that closely.

The core A900 CPU set 12201A / 12202A / 12203A / 12204A appear to be
common enough on eBay if you are willing to pay somewhere in the range
of $50 - $175 per board. $200 for a complete CPU board set might not
be too bad for a hobby budget, but you can easily go 2x or more higher
than that buying the boards individually.

The 12220 768KB and 12221 3MB boards are also common enough, typically
somewhere in the range of $50 - $175 per board. The 12221 8MB boards
seem somewhat rare. The A400/A600/A700 12103 memory boards are not
compatible with the A900.

At a minimum you need either a 12005 serial card or a 12040 serial mux
for a console interface. Both of those are fairly common, although you
might pay more for cables than the boards if you don't build cables
yourself. There are several firmware versions for the 12040 mux. If
you have a D mux you need need VCP firmware 4020 or higher on the
12203A cache controller.

As you also said you need a 12009 HPIB card for a storage interface.
Running HPDrive on a PC to emulate disk and tape drives works well if
you don't have any real HPIB disk and tape drives. I managed to pick
up a 12016 SCSI card. Those are rare and expensive.

The best deal would often be on a complete chassis/backplane/PS box
with the complete CPU card set, if you can ever find one, rather than
buying individual parts here and there. I got a complete A900 box and
boards from Sellam for somewhere around $200, but that was a few years
ago now. I should get rid of a lot of the stuff I have collected over
the years, but don't plan on getting rid of the A900 anytime soon.

If you do get a working A-series up and running, the RTE-A
installation tapes are available on Bitsavers.

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