HP-41cx educalc module?


I found a working hp-41cx and there is a strange mondule (for me...) install in it : on the back of the module a silver tape label "EDUCALC MODULE SERVICE" and on the normal place for module labeling another silver tape label "Double - A531D" What is that module and how to wake it up? Is it "homebrew" module? What is educalc?

ok, i stop...

Thanks for hints!


Educalc was THE mail order supplier of HP calculators and accessories for many years. They were located in California, USA. About 3 years ago, they went out of business (since HP started selling through large retailers).

As far as the module you have, I know that service modules were made by HP to diagnose 41s with problems. But I did not know Educalc apparently made some. Perhaps someone else may have seen/used one of these modules.

If you do a CAT 2 it should list the programs on the module.



I tried CAT 2 and no program for this module


Try a different port. Turn the machine off, pull it out
and try another port.. Sometimes oxidization forms and
another port (or just the action of plugging it in and
out) will help.

It might be an autoexecute type of module too, like the
cassette duplication module...


Note that only a C or a CV will list the programs with f CAT 2; the CX will just list the modules and ROM's installed.

Hoever bill's remark is totally valid, should the module not being recognized try another port.


jim had some deal to double up x-mem (and other) modules in the same case to save ports. this may be one of thoes. check how much extended you have; if it's all 600 then you have one of thoes.


I assume it added EXTENDED MEMORY also. Check it on a CX with CAT 4. Should show 124 in the X Register. With one EXTENDED MEMORY MODULE, 362, or two EXTENDED MEMORY MODULES 600. You can also check it on a C or CV with the EXTENDED FUNCTIONS MEMORY MODULE by executing EMDIR.

David White (now David Ebras-White) use to do a lot of the soldering foe EduCALC and authored the "Butcher's Block" articles in the PPC Journal, which included a description of module doubling and tripling. See:


for a little longer write-up


I try cat 4 on my CX with the module and it gives me 600; without the module it is 124 so this is a memory module sold/built by educalc... Thanks all!

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