HP-41 Module conflicts or what?


Sudden erratic behaviour (weird tones beeping, flashing display, funny symbols, locked display, had to take batteries out to unlock the calc, then more erratic behaviour when turned back on etc). Config:

HP-41CX with the following modules installed in the various slots:

X-Memory - Financial I

Math/stat - Navigation

The one I added last that caused erratic behaviour is the Navigation module. I then took the Math/Stat out and moved the Navigation module in its place. Then it's all ok again. Hm...

Any idea why?


Can you recreate the fault by putting the modules back where they were?


Check if any of the software modules you use have

either same XROM numbers and/or same function names.

This information can usually be found in the associated manuals.

Additionally, you should place the X-Memory into the lowest numbered slot.

AFAIR the latter is not mandatory, but recommended by HP.



XROM numbers should not be an issue. Math = 1, Stat = 2, Navigation = 14, Finance = 04. Only cuprit I can think of is the Finance mod, if it is a different one (like GMAC or so). To check, plug it in and enter a program using one of its functions and then plug it out and check the program. It will show the XROM number for that function. If it is 1,2 or 14 you have found the issue...




Hi, Geir;

I had seen some problems related to erratic behavior and, in extreme cases, calculator locked, mainly because of bad contact between the Battery/IO assembly and the keyboard PCB. In some cases, broken/cracked screw posts are the case, and solutions are diverse. Do you have the means to check if the both upper and lower halfcases are firmly together? Just slightly (SLIGHTLY) try to pull them appart, close to the LCD assembly. The simplest feeling of having them moving appart from each other is enough to certify if there is a case problem.

Also: please, don't be mad with me after reading my suggestion, because it is more likely that you'd have done this if you had the means to, but I can't help asking: do you have the means to perform a ROM checksum in these modules?

Hope this gives you some new clues... Let us know how it goes.


Luiz (Brazil)


Hi guys,

Thanks for the input.

1) Problem can be replicated.

2) The calculator is very firm, not possible to move apart at all.

3) No means of seeing ROM checksum

4) I will try another CX I have. I'll let you know.

Edited: 22 Dec 2005, 4:45 a.m.


Sudden erratic behaviour (weird tones beeping, flashing display, funny symbols, locked display, had to take batteries out to unlock the calc, then more erratic behaviour when turned back on etc).

Sometimes that kind of behavior can be caused by a module that is not inserted fully, or that has loose-fitting or dirty contacts, etc. It may happen more with some module/port combinations than others. For instance, I have a 41CV that behaves that way when my barcode wand is inserted in one port, but it works fine in the other three ports. Other modules work fine in the "bad" port, and the wand works fine in all four ports of my 41CX.

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