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There's a seemingly-nice 9810 up on eBay:


Any special caveats on this model? I'm considering a bid, but this is way earlier than any other desk calc I have...

Depends on what you mean by 'caveats'. Be warned that it's not a particularly good calculator without a maths ROM (you don't get trig functions or logs in the standard machine), and that the printer-alpha ROM is useful too.

As regards keeping it going, it's mostly 74xx and 74Hxx TTL inside, with Intel 1103 (1K bit DRAMs), small PROMs and some HP custom ROMs for the firmware. It's more maintainable than, say, an HP35. But it's not a trivial machine to debug. It's bit-serial, which means you won't trace faults without a 'scope or logic analyser.

I guess the final comment has to be that I like my 9810, but then I like boards of TTL chips :-)

The machine on Ebay has the math and printer/alpha ROMs.

I've acquired a few desktop machines over the years-- a 46, a 9815, and a 9825. Mostly they stay in a closet, but the 9810 is very seductive to me. My limited electronics skills-- I can replace defective 5-digits display modules in first generation handhelds, but that's about it-- would mean I'd be unable to repair the 9810 if anything ever went wrong with it.

I'm trying to figure out how much to bid on it. In the past, these older desktops have gone for either very low or very high prices...

I don't want this to appear as a flame (it's not!), but I'd like to say "You're never too old to learn" (and FWIW, I am still learning about calculators, computers and electronics!).

You may not be able to repair a 9810 _now_ but that doesn't mean you'll not ever be able to repair one. I didn't know much about computers when I got my first mini (a Philips P850), and I had to trace a logic fault on the second day of owning it. I was really 'thrown in the deep end' when I got my PDP11/45, but I figured that one out too, and I learnt a lot in the process.

Yes, the 9810 is complicated, and being bit-serial it's not easy to debug, but it's possible, and there are people here who can talk you through it.

Although Tony is not a big fan of board swapping (some faults can kill a good donor board) if you have a known good machine to work with it REALLY helps in isolating problems in these machines.

Sure...I'll just use my _other_ 9810 if I have problems. All I have to do is win another auction. After this one...

Yes, and it would help if one of the auctions is for a good machine. Or at least one that has a good version of your bad board.

I was given 2 non-working 9810s at the same time, the donor suggested I might try swapping boards around to get one of them working.

Needless to say I didn't waste time doing this (and actually, it wouldn't have helped anyway -- the 'better' machine had a fault on the I/O interface PCB, and that board, along with quite a few others had problems in the other machine). Instead I figured out how to fix them properly, fixed one, then, I will admit, tried the boards from the other machine in it one at a time to see which had serious faults. I then debugged those the old-fashioned way.

98x0 machines are a bit hard to debug becuase they're bit-serial, so everything is changing all the time :-). But given a logic analyser (the HP logicDart is ideal!), it's quite possible to find faults.