HP41 - check routine Is there any method?


I miss my HP41C that was stolen. Now I´m going to buy one.
I want to know if there is some way to check if the calculator is running perfectly.
Is there some sequence of keystrokes to trigger an internal checking routine to know if the calculator is working OK?
Please send copy of answers to my e-mail.
Best regards, Horacio


The 41C family does not have any built-in self-test, unfortunately.

If you can perform simple calculations from the keyboard, and if the memory is all present, it's very likely that there's nothing wrong with the electronics.


Eric's right. Although some machines prior to the HP-41 had self tests in them (the Spice series), this feature wasn't implemented on the 41. I might be misremembering a conversation with one of the 41's designers, but I think the reason was that, since the 41 was both extremely complex, and not self-contained, it was too hard to do an acceptable job of self-testing in the space available in ROM. They ended up with the Service module instead, but that was never released to customers.

If I were checking out a used 41, I might try something like the following to reassure myself that the unit was probably okay:

  • I'd remove all the modules, port caps and batteries, and physically examine the machine, looking specifically for evidence of corrosion in the battery compartment, wear on the port contacts, and liquid spills on the keyboard and under the display
  • while holding the top (display end) of the 41 in my left hand, I'd twist the machine around its long axis with my right hand and look for signs of looseness along the seams up the side of the machine; there should be very little play in a 41 that has not been opened
  • I'd examine the rubber feet to see if they'd been removed,
    and I'd pick at the edges of the keyboard overlay to see if it was loose
  • I'd make sure that the U-shaped plastic separator that fits between the front and back halves of the case is in the right way around; some people who disassemble their 41s put this in back-to-front, and you can tell by touch and by looking down on the 41 towards its I/O ports
  • With known good batteries in the machine, I'd hold down the '<-' button, press and release 'On', and make sure the machine comes up with 'Memory Lost'.
  • On a CX, I'd then press shift-on and expect to see a ticking clock; whatever it said the time was, I'd set it to something else, make sure the new time came up, and then I'd turn the machine off and on again
  • At this point, I would not expect a 'Memory Lost', and I would expect shift-on to show me that the clock had not reset or become garbled.
  • I'd enter '1', press enter three times, expect to see 1.0000 in the display; I'd then press '+' repeatedly, and I'd expect to see the number in the display become 2.0000, 3.0000, 4.0000, 5.0000, and so on for as long as I liked
  • I'd turn the machine off and on again, and expect to see whatever number was last in X still on the stack
  • I'd go into ALPHA mode, and I'd enter things like +,8:*.O; over and over, and look carefully to make sure all the segments in all 12 display positions behaved themselves
  • I'd go into PRGM mode and look for 00 REG 46 on a 41C, or 00 REG 219 otherwise
  • I'd do SIZE 000 and expect to see 00 REG 63 or 00 REG 319, and I'd do SIZE 063 or SIZE 319 and expect to see 00 REG 00
  • I'd then start pressing '+', and I'd expect to see PACKING TRY AGAIN on the fifth one
  • I'd exit PRGM mode, and repeatedly press sigma-+ and expect to see 1, 2, 3, 4,... appearing in the display
  • Then, I'd press BEEP, and I'd expect to hear the 41 beep
  • If this were a half-nut, I'd try to get it to whine by repeatedly making it BEEP and, while this is sounding, pressing ON and Enter^ -- after a few goes, you should be able to warm-start the OS with the bender port open, and you'll be greeted with a 6kHz tone whenever the CPU is active
  • If you manage to make it whine, you can then just press and hold each key on the keyboard, and expect to hear a consistent whine while you hold it down -- it's not the best keyboard test in the world, but it can help you to spot dodgy contacts; otherwise, you need to make sure that every key does what it's supposed to, and feels okay
  • If this is a CX, you can then press shift-ON to bring the clock up, and you should hear the 41 chirrup once a second, as it wakes up to update the display
  • Once you're fed up with the whining, just go BEEP again to stop it
  • The PRGM and SHIFT annunciators should already have been seen to be working -- I'd check the other annunciators by setting flags 0 to 4, GRAD mode, USER mode, and go into ALPHA mode and PRGM mode (I don't know of a way to force the BAT annunciator on without having something like a Zenrom handy, or very carefully worn-out batteries)
  • If I had any plug-in device handy (such as a Math ROM), I'd plug it into each port, and make sure it showed up in CAT 2

By this point, I'd probably have a fair degree of confidence that the machine was behaving itself. If I had a CX, I'd probably also read and write some data to its built-in extended memory -- I'd probably just use 'ED' to write something into a file, and make sure it was still there.

I don't know if this is helpful or not, though, or if it just shows that you should avoid me getting my hands on your precious 41. :-)

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