New member introduction, questions on HP 21XX series machines, reliability and maintainability

From: Jay West <>
Date: Wed Oct 29 21:25:30 2003

Well William, you've come to the right place. My particular obsession is
HP21xx machines, and I've got about 9 or 10 of them. While I do have a fair
amount of DEC gear, TONS of heathkit, and some DG stuff on the way, the
HP21xx line is my passion. I also have tons of 790x drives, 13037
controllers, racks, etc. etc.

I know there are a chunk of HP 21xx collectors here, about half active and
and about half lurking. If you run into any issues I'd be happy to help. On
to your questions....

> interest in old computers, and rescued a "straight-8"
> many years ago when I didn't think anyone else
> thought of it as anything more than junk.
The holy grail *drool*

> It was at
> least minimally operable when I obtained it, but I
> went off to graduate school before I could find any
> software for it, and it's been in storage at my
> father's office in Florida for ~15 years now.
There is plenty of software on the net, and among the listmembers here, for
the 8's.

> After some research, I have settled on the HP21xx
> line as a good candidate. These seem to be very nice,
> well-built machines with a reasonable architecture,
> a good paper-tape BASIC, and a full complement of
> "blinkenlights".
What? The HP21xx wasn't your FIRST choice over the straight-8? I'm HURT! :)

> It seems that these machines are
> actually still used, however, and I've been quoted
> some pretty steep prices from a nearby dealer in
> in used HP gear.
Correct... they ran BCS, DOS, MTS, RTE, TSB, RJE, all kinds of different
stuff. But RTE is what they still run a lot in industry, mostly in test &
mesurement, and in the military. This keeps the prices somewhat high for
them. On the bright side, they aren't terribly rare. At least the 21MX's
aren't. The 2100's are pretty hard to find, the 2114/2115/2116's seem to be
extremely hard to find. Well, except... search Ebay for 2116B and you'll see
a beauty for sale!

> I'd be interested in comments and advice for a
> prospective 21xx owner from those on the list who own
> these machines or have used them. I'm particularly
> concerned about reliability, since at the price I
> expect to pay, I want to keep it operating for a long
> time to come. How difficult and expensive are they to
Ok, Bob Shannon will vehemently disagree with me... but I think the 21MX's
are extremely reliable (he'll agree there), but I think the 2100's are
almost as reliable (he'll disagree here). The core memory section can be
very troublesome to work on (to me at least) in the 2100. But at least with
the 2100's, once you get one working, it generally runs forever. All the
older HP stuff is built like a battleship, and pretty easy to work on. And
very well engineered.

>How available are contemporary replacements
> and/or new old stock for the ICs?
The bus driver IC's (DTL if I remember right) are scarce... BUT... there are
so many 21MX's still in production use, most cards are plentiful, as are
thus dead cards with bus chips that can be snagged. Microcode and boot roms
(blank) are not impossible to find, but a bit scarce.

>Are there any
> proprietary components that are particularly prone to
> failure or hard to replace that I absolutely must
> obtain up-front as spares?
servo platters and heads for 790x drives. Air filters. Spare cpu set. A
decent vintage prom burner to save off rom images. Spare power supply. If
you want to run TSB, the 12920/12921 mux set is required, and rare.

> What about the core stacks
> themselves? The dealer that I talked to seemed to
> think these were problematic (though I did not speak
> with his technicians), while my instinct would be that
> the core itself (not the driver electronics) would be
> among the most reliable and stable components, barring
> visible corrosion damage.
You are correct. The core "boards" go bad fairly frequently, pretty much
never the core stack itself though. If it is a bit stuck on or bit stuck
off, the repair is trivial. Why do I get the impression it's crisis that
you've been talking to? :) Otherwise, the XYD and ID boards seem to be the
more problematic.

> Also, any suggestions on places to look for these
> machines on the cheap would be welcomed. What I'm
> most looking for is a 2115, but would likely be
> interested in the somewhat later 2100 as well.
As I said, 2115 will be kinda hard to find... crisis may be your best bet,
albeit for real $$$. And there's a gorgeous 2116 on ebay. 2100's are around,
but getting scarce. 21mx's are everywhere. Try scrap dealers. I have lots of
21MX's available for trade, and lots of associated peripherals.

ok Bob, you know you're itching to chime in here :)

Jay West
Received on Wed Oct 29 2003 - 21:25:30 GMT

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