Help: HP-41CX and IR module


I just got an IR module for my HP-41CX. Unfortunately it does not seem to work.

I have an Advantage module in port 1 and that's it. I have tried the IR module in the other ports but the calculator does not seem to recognize it. It does not show up in the catalog and the commands are not recognized.

I saw a bit of corrosion on the contacts of the IR module and cleaned them off but that did not help.

Any suggestions on how to troubleshoot further?



Ahh. After playing around some more, I have gotten the IR module to work. The problem appears to be with the calculator and slots 2 & 4. If I have the Advantage module and the IR module in slots 1 & 3, all is good. If I have them in 2 or 4 they are not recognized.

The calculator looks really clean - no corrosion on the contacts. What other types of issues could cause two of the slots to be non-recognized?


Hello Marcel,

I have tried all the combinaison of those two modules and I was always able to print.

Ad1:IR2, Ad1:IR3, Ad1:IR4,
Ad2:IR1, Ad2:IR3, Ad2:IR4,
Ad3:IR1, Ad3:IR2, Ad3:IR4,
Ad4:IR1, Ad4:IR2, Ad4:IR3

41CX Halfnut (2814S...)
Advantage (8617)
82242A (2922)
82240A (2825S...)




Thank you for the information. It is good to know that it should work. (Although it is not good to know that my 41cx has something wrong with it)



Hi Marcel,

This type of side-malfunction (so to say) is mostly caused by a poor/damaged/cracked screw post (the upper ones), which prevents the I/O flex-PCB from making a reliable contact with the keyboard PCB.

My advice would be to take your HP-41 apart and check/fix these upper screw posts.

Also, once opened, a good contact cleaning with isopropyl alcohol won't hurt :-)

Hope this helps.

All the best from Dominican Republic.



Thank you for the advice Diego. I searched around a bit and it seems that this topic has been covered many times but there are different opinions on the best way to fix the posts.

What is currently thought to be the most straightforward and reliable way to fix them?


Be aware that if the screw post is half-dead it may end up completely broken when you take the unit apart and put it back again - so be prepared for some repair action.

I think the best should be replacing them with metal threads, which requires fine crafting and precision milling, certainly not for my poor skills.

Edited: 13 Nov 2013, 12:01 p.m. after one or more responses were posted


Sigh. That is not good news, as evidenced by the two dead 32Sii calculators which started out with minor keyboard problems before I tried fixing them.


FYI, here is a detailed description of broken posts fixed with metal standoffs: HP-41 Permanent broken Post Fix


Diego; Did you change islands (and sides of the ocean) or are you on vacation? -db


He's oscillating. ;)


At what frequency? I'll try to tune him in.


Hi all,

Regarding my 'oscilation' :-), it has a quite long 1/f (f = 9.56e-8Hz) of around 4 months with a some 1/4 duty cycle at the East (Canary Islands) side and remaining 3/4 on the West (Dominican Republic) side.

I'm however on-line most of the time and my inbox is happy to receive your messages ;-)

Back to the original thread and the 'post repair'; unscrewing them will more like cause no harm whatsoever and, since you have (want) to fix it, it is mandatory to take them apart, so...

Although Ángel's comment on the 'definitive' metal posts replacement is undoubtly true, there are many cases in which less severe repair procedures may lead to good reliable results.

Once you've removed them, if you dont feel confident on the acctions to take to fix the problem yourself just post here some hi-res pics of the damaged part so others can have a clear idea and offer convenient advice.

Hope this help.

Best from Caribbean.



Thanks for the advice Angel, Diego and Didier. I will take it apart this weekend and figure out next steps from there.


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