Mystery HP41 CX


Hi All

One of the nice things about being a collector is occasionally coming across a mystery custom machine.

Its a 41CX with a double DIP switch on the opposite side to the charger port, it has been double speeded (determined by the BEEP tone). The DIP switch appears to make either the Navigation Rom or ZenRom change visible in CAT 2 (or both).

So the questions

(1) Whose mod might this be

(2) Is there a way of uploading new software ROM's to it?

Thanks in advance



Most likely the PCBs of the two modules are build inside the 41. The switch connects the ISA-line of the modules to the calculator.

If the switch is turned on, the build in module is hardwired to one of the HP41 ports and you cannot use this port for another ROM module.

Beside some others I did such kind of mods for many people in europe. You could even buy a PCB to build in 4 modules. Here is a picture..

There ist no way to upload other software as it is a hardware mod with ROM modules.


Hello Winfried

Thank you for your informative reply, I *may* open the machine up to see whats going on now...and which ports it overlays (though i could of course test that with a module too)


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