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HP Forum Archive 08

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HP-41C: Port problems
Message #1 Posted by Juergen Rodenkirchen (Germany) on 19 July 2002, 7:06 p.m.

Some days ago, I posted a note about a module conflict on my HP-41C in connection with the use of Memory Modules (original message will be attached below). In fact, I did receive a few responses: thanks again to all who made the effort to write! Alas, after checking and trying out what I was told (cleaning contacts ond taking care of the correct port order), it seems that my problem is still not solved (same behaviour as before, that is). Besides, further experiments with a QUAD MM showed the following: Installed in port 1 or 4, the machine allows access to the full of 319 registers. Unlike that, if the QUAD would be plugged into port 2 or 3, SIZE 000 just shows 128 registers, indicating that only another 64 + 1 registers will be addressed. Any idea how this can happen and how this can get fixed? Thanks for your time!

< Original Message:

I have an HP-41C which shows some kind of failure when a Memory Module (MM) is plugged in (might well be that the same failure would show up with a Quad- or a completely different module, though I haven't checked it yet). The machines "operating mode" depends on the port that is occupied by the MM: When the machine is operated with a MM in port 1 it seems to work correctly (at least, the MM is recognized by means of SIZE). If a MM is plugged into ports 2 or 4, a very faint (actually barely perceptible) and high pitched tone is emitted by the machine and it doesn't respond to the keyboard anymore. In port 3 the MM is not recognized at all. Otherwise (without MM that is) the calc seems to work fine. Does anyone have an explanation for this behavior? >

Re: HP-41C: Port problems
Message #2 Posted by Vieira, Luiz C. (Brazil) on 19 July 2002, 11:14 p.m.,
in response to message #1 by Juergen Rodenkirchen (Germany)


I still believe you have some contact problems, but with the new info, I'd check the integrity of the flex circuit itself, the one wrapped around the IO/BATT assy. It may have broken cooper trails. It is not that impossible...

Also, the contacts between the IO/BAT assy and the motherboard. If there's anything wrong in there, the modules' contacts may be fine, and the port's contacts may be not fine.

Well, you'll have other ideas, for sure. I have seen (and had my own experiences) that bad connections and bad contact are the most usual problems in HP calculators. A bit of solder and cleaning brought some fellas back to life (in this very week, I resoldered two HP12C, one HP11C, some SMD's on a mishandled HP48 and upgraded my HP42S to 32K! Busy days, when soldering is the special).

Cheers and success.

Re: HP-41C: Port problems
Message #3 Posted by Andrés C. Rodríguez (Argentina) on 20 July 2002, 12:49 p.m.,
in response to message #1 by Juergen Rodenkirchen (Germany)

I have had no Quad module to experiment with, and also my HP41 has some contacts problems, so my suggestion is mainly from similar but not equal experiences and some educated guessing.

The standard memory modules must be installed always in a consecutive manner and starting from port 1. I suppose the calculator searches for RAM starting at port 1 addresses, and then at the following ports. If it finds any unused addresses, it will assume there is no more RAM to look for. It may be similar with the Quad, so unusual behavior in ports 2,3 or 4 as you observed may be caused by conflicting addresses or because the firmware in the calculator finds an unexpected condition and "hangs up" or triggers other error conditions.

Other modules such as extended functions and extended memory also have specific rules specifying which sequence the ports are to be used for.

My guesses may be wrong, and it may well be that the Quad has fixed (hardwired) addresses, since it occupies a defined address space in full. In that case, it should work at any port. Please see the Quad Module documentation to see if this is the case. In the meantime, using it at port 1 shouldn't be an issue.

Re: HP-41C: Port problems
Message #4 Posted by Vieira, Luiz C. (Brazil) on 20 July 2002, 6:47 p.m.,
in response to message #3 by Andrés C. Rodríguez (Argentina)


There is a particular case. I have a 41C in the box (I mean, disassembled) and four memory modules. I remember when I had only one module I could plug it in any port; the fact is that only when it was plugged in Port 1 I could use all memory for programs. In ports 2, 3 or 4 I should "map" the 64 registers, because a gap would exist. It seems to me the 41's OS searches for memory in a bottom-to-top scan (Maybe it's faster). I remember I could access higher registers, store numbers in there, switch the calculator off, move the memory module to another port, switch it on and search for the register that would contain the numbers I stored.

I did not have any other module, I could get them (X-Functions, X-IO and Navigation) only after buying a 41CX. I never used them in a 41C, so I do not know what sort of reactions may come with modules between two memory modules.

At the time I was writing this post, Juergen answered; but I would mention that it is stated in the 41C manual that the Quad Memory Module (QMM) can be plugged in any available port. No restrictions.


Thanks a lot for your inputs!
Message #5 Posted by Juergen Rodenkirchen (Germany) on 20 July 2002, 3:25 p.m.,
in response to message #1 by Juergen Rodenkirchen (Germany)

Luiz, Andres, thanks a lot for your valuable info concerning my current problem. I'll try to "digest" what you told me and hopefully be able to fix this HW problem from your hints! B.t.w. Andres, the QMM documentation says that it can be used in any port, proving your guess the QMM having a fixed address space :-) Thanks again!

Re: Thanks a lot for your inputs!
Message #6 Posted by Andrés C. Rodríguez (Argentina) on 20 July 2002, 7:13 p.m.,
in response to message #5 by Juergen Rodenkirchen (Germany)

Ok, so now I know the Quad is not port-dependent (I first thought otherwise, now it is clear) Thank you, Juergen and Luiz!

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