HP-48GX Calculator Disassembly: Case Rivets

The keyboard on my trusty HP 48GX calculator finally deteriorated to the point of unusability, so I tore the thing apart following the useful instructions there. The warning about applying force to the rivets that hold the case halves together gives you not the faintest concept of how much force is actually required to pry the mumble thing apart at the battery compartment; I finally invoked force majeure with a chisel scraper

HP-48GX case rivets
HP-48GX case rivets

I expected the calculator would not survive this operation and I wasn’t disappointed.

An HP 50g is now in hand. Here in late 2011 I’d expect HP’s top-of-the-line RPN calculator to sport a crisp high-resolution display, but noooo the low-contrast 131×80 LCD seems teleported directly from the latter part of the last millennium. The manuals are PDFs, which is OK, but their content is far inferior to the HP 48GX manuals. In particular, the editing / proofreading is terrible. I infer that the HP calculator division can barely fog a mirror and is on advanced life support; HP’s diverting all their money to, uh, executive buyouts or some other non-productive purpose.

The fact that HP sells new-manufacture HP 15C calculators doesn’t crank my tractor, even though I lived and died by one for many years. A one-line 7-segment display doesn’t cut it any more, even if the new machinery inside allegedly runs like a bat out of hell.

My HP 16C, now, that one you’ll pry out of my cold, dead hands. At one point in the dim past, I’d programmed the Mandelbrot iteration into it to provide bit-for-bit verification of the 8051 firmware for the Mandelbrot Engine array processor I did for Circuit Cellar: slow, but perfect. That calculator has a low duty cycle these days, but when I need it, I need it bad.

14 thoughts on “HP-48GX Calculator Disassembly: Case Rivets

  1. Hmmmm. HP’s RPN. A thinking man’s calculator. Had the HP 25 (red leds, ewww), 41CX, 15C & 12C. I’m not proficient but they sure are useful.

    1. I’ll admit the 50g does symbolic integration far better than I ever did, but the truth is that I don’t do that any more…

      The calculator’s out-of-the-box default setup enables a thin layer of infix notation pasted over the RPN; the manual immediately advises you to flip that switch and use pure RPN. The algebraic syntax seems to be there to allow the “textbook” equation display & solving that forms a very small part of what (IMHO) engineers actually do with calculators. I suppose it makes the calculators marginally salable in schools, a market HP has pretty much blown.

  2. Ah, another RPN weirdo…. :-)

    Sorry to hear your 48GX didn’t survive the surgery. Many years ago I had to do similar surgery on mine (of the 48G and the 48GX I had, it was the GX that decided to develop a problem – I’ve forgotten whether with the keyboard or display).

    IIRC, there were 2 methods of opening it, one involved removing the thin metal keyboard overlay. After trying that first, I realized it would so thoroughly ruin the looks of the thing I went for the other way, removing rivets. It worked, though during prying it apart with a large screwdriver I did ruin a SMD resistor on the board. Fortunately had the schematic and spare resistors. IIRC, there was a flexible strip somewhere to the PCB (from keyboard or screen?) that didn’t make proper contact. I put a piece of folded-over paper under it and glued it together again. It has been working fine ever since (must be about 10 years ago).

    Alas, I hardly use the 48G/GX anymore. In ’95 I bought a HP-32SII (now I wish I had gone for the HP42 instead, but that was *way* over my student’s budget at the time). Used that for many years, then used the 48G/GX for many years, but now I only use the 32SII anymore – lasts forever on its batteries (had to replace them only twice over the years – 3 tiny LR44s…, but, more importantly, it’s faster than the 48. Often the 48 would miss a keypress because it couldn’t keep up (even with empty memory). And as I hardly used the 48’s capabilities anyway, I’m now using the 32 again – which is also MUCH easier to quickly program than 48’s user-RPL.

    The 32 is now my steady companion.

    Best thing…. few people want to borrow it… it has no ‘=’ key ;-)

    1. prying it apart with a large screwdriver

      Yeah, that sounds about right. [sigh]

      The plastic rivets make sense from a manufacturing perspective (no messy screws / threads / assembly), but for repair they’re terrible. Of course, you’re supposed to junk the calculator and buy a new one, which makes perfect sense after nearly two decades.

      The 15C runs forever on three watch batteries, while the 50g has a reputation for frequently munching its quartet of AAA alkalines. I suppose that’s the tradeoff for all that ARM machinery under the hood. The 48gx ran for about a year on its trio of AAA cells, albeit in my relatively low-duty-cycle usage.

      I must bashfully admit that I have a pair of dirt-cheap Sharp calculators in the shop, where they occasionally run afoul of a coolant spray or swarf shower, specifically for quick conversions and suchlike…

      1. It ran a year for you on those 3 alkaline AAAs? Impressive. For me normal usage was 3 months…. I kept a tiny bit of paper in the battery compartment where I notated the date new batteries were installed (I also keep all fuel receipts in the ashtray of my car, going 12 years back, and I write the date on CFL bulbs when I install them….)

        In school we used TI-30 stats, and those are my ‘junk’ calculators (one in the car, in the shop, in the shed, etc.). I can usually find them pretty cheaply at flea markets, as the things were the normal highschool calculator here in the mid-80’s. Because I’ve spent most of my highschool years using one, I can blindly find my way on them…. though I still have a habit of entering numbers in RPN on them…. Come to think of it, those TIs don’t need fresh batteries often either….

        1. and I write the date on CFL bulbs

          Huh. You, too?

          At one Family Gathering I asked how many of my cousins wrote the purchase date on long-lived items; a surprising number of them confessed to that compulsion… so it must be genetic!

  3. OMG!…. what has happened?! Just had a look at the 49 and the 50…. and they look disgusting (no matter how powerful they may be – I can’t judge that).

    I always loved the sobre, stylish tasteful look of HP calculators. Seems they were made for (wannabe) professionals…. but these new calcs look like they’re made for schoolkids :-(

    1. the sobre, stylish tasteful look of HP calculators

      I suppose that vanished when HP decided to chase a market they had no clue how to capture.

      The display is a real disappointment. I can cope with the rest of the thing, although some the empty space around those four cursor buttons would be better used to chivvy a large Enter key over on the left where it belongs.

  4. What is it with crusty engineers and the old HP RPN calculators?

    An HP41CV was my first real calculator in college. I had the card reader, bunches of modules, hacker guides etc. I “built in” a time module by using wire-wrap soldered to the gold foil connector (long before I really understood why gold is used as a contact :( ), so it was “almost” a CX.

    I’ll credit programming the HP-41 for much of my early programming understanding. Assembly is not daunting after mastering programming a HP-41 :)

    Now the “V-41” emulator from http://www.hp41.org (login required, sorry) is on every machine, and another emulator on the i-phone ( http://itunes.apple.com/us/app/i41cx-rpn-calculator/id292619450?mt=8 ). So even though my physical HP-41 is deep in the back of a drawer, I have virtual ones in reach all the time.

    My daughter is not a math fan, but needed a graphing calculator for schop. We got her a TI nSpire CX:


    and a few days ago she mentioned that “math is kinda fun with the calculator”. That calculator is pretty amazing. Also, it is $137 is weak 2011 $US, where the price of a HP-41CV was like $300 much stronger 1983 dollars.

    1. What is it with crusty engineers and the old HP RPN calculators?

      We imprinted on them, early and hard…

      TI managed to get their calculators into high schools and that’s the end of that story.

      “math is kinda fun with the calculator”

      After you understand and master the fundamental operations up through simple integration & differentiation by hand, then there’s no reason to ever do that stuff again. No interesting physical situations succumb to closed-form integration or differentiation, so you may as well feed the equations / coefficient into a calculator and let it do the heavy lifting.

      FWIW, the original HP 35 came out when I was in college and my folks asked if it would be helpful. I told them not to buy it, because calculators would only get cheaper and better: one of the very few correct predictions I ever made! So I was in the last generation of engineers who routinely used slide rules to solve actual problems…

  5. Somewhere around here I have the shards of a homebrew calculator I made while in college. Could not afford the real thing, so I bought a Cal-Tex chip (CT5005: 4 functions with memory) from PolyPaks, scrounged a keyboard and 12 tiny numeric led displays, and wired up the whole thing in a small aluminum Bud box.

    It sort of worked, but it was kind of hard to tell because those dozen LEDs ran the battery down almost instantaneously :-)

    Seemed like a good idea at the time, but all in all this mostly served to heighten my appreciation of the HP calculators I later adopted.

    1. bought a Cal-Tex chip … from PolyPaks

      Polypaks: “No time to test them!” Now there is a name I haven’t heard in a while…

    1. Wish I’d found that before I killed the poor thing! The keys might have remained dead, but I would’ve felt better about it…

      Thanks for the note: I hope someone else will benefit from it.

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