HP-41CX with built-in HEPAX module

[Jurgen Keller]

Today I got an HP-41CX for testing/refurbishing. After inserting batteries I was happy to see that it still works perfectly. However, I was quite surprised when I did a CAT 2 and saw '-HEPAX 1C' on the display. So it looks like this 41CX has a built-in HEPAX module! Quite cool, a very uncommon modification, at least I never saw such a variant before. Furthermore, it has a red switch on the left side to enable TURBO mode as you know it from 41CYs, for example. HEPROOM displays 2610 so my understanding is that it's a 16K HEPAX module, right? Does anybody know of such a modified 41CX? If so any background information will be highly appreciated.

Sorry, have to stop here and play around with this special 41CX! :-)

[KimH]

Hm…. Do you have a picture of the turbo-switch - maybe this is one i have made…..

(03-23-2022 07:08 PM)Jurgen Keller Wrote:  Today I got an HP-41CX for testing/refurbishing. After inserting batteries I was happy to see that it still works perfectly. However, I was quite surprised when I did a CAT 2 and saw '-HEPAX 1C' on the display. So it looks like this 41CX has a built-in HEPAX module! Quite cool, a very uncommon modification, at least I never saw such a variant before. Furthermore, it has a red switch on the left side to enable TURBO mode as you know it from 41CYs, for example. HEPROOM displays 2610 so my understanding is that it's a 16K HEPAX module, right? Does anybody know of such a modified 41CX? If so any background information will be highly appreciated.

Sorry, have to stop here and play around with this special 41CX! :-)

[rprosperi]

I recall hearing something about this back the 80's, but there was no specific information or proof. For all I know, the whole thing may have been started by someone saying "Hey, let's start a rumor that there is a 41CX with HEPAX integrated...". I never heard more about it and never saw one, and in fact forgot about it until your post today.

From what I've learned about the HEPAX ceramic circuit boards from Diego, they are mighty fragile and so whoever made this has well above average skills. I'd say really, really don't open it, despite the obvious temptation to take a peek.

We look forward to hearing more about it.

Hint: Assign "HEPAX" to [shift] [1/x] so you can quickly do [shift] [1/x] [1/x] for HEPAX CAT-2 listing.

[charger73]

Jürgen, you're a lucky man ;-)

[Jurgen Keller]

(03-23-2022 08:50 PM)KimH Wrote:  Hm…. Do you have a picture of the turbo-switch - maybe this is one i have made…..

(03-23-2022 07:08 PM)Jurgen Keller Wrote:  Today I got an HP-41CX for testing/refurbishing ...

Here we go


It looks like the red switch used für 41CYs, so maybe W&W did the modification. Did you work for them?

[Jurgen Keller]

(03-24-2022 02:19 AM)rprosperi Wrote:  I recall hearing something about this back the 80's, but there was no specific information or proof. For all I know, the whole thing may have been started by someone saying "Hey, let's start a rumor that there is a 41CX with HEPAX integrated...". I never heard more about it and never saw one, and in fact forgot about it until your post today.

From what I've learned about the HEPAX ceramic circuit boards from Diego, they are mighty fragile and so whoever made this has well above average skills. I'd say really, really don't open it, despite the obvious temptation to take a peek.

We look forward to hearing more about it.

Hint: Assign "HEPAX" to [shift] [1/x] so you can quickly do [shift] [1/x] [1/x] for HEPAX CAT-2 listing.

Thank you for the information and the hint, Bob. I was indeed tempted to open it, however, it's not mine and even then I'd probably wouldn't do it. I've seen so many broken posts and encountered so many other problems after opening HP-41s that I open them only if there is a real need, not just curiosity.

Back in the 80ties it think it was quite common to build modules into 41s just to keep some ports free for other stuff. So, why not a HEPAX?

[Jurgen Keller]

(03-24-2022 06:18 AM)charger73 Wrote:  Jürgen, you're a lucky man ;-)

Tobie, it's not mine, I just got it for testing purposes and rebuilding the battery pack. At least, I can play around with it a bit.

[Jurgen Keller]

The owner of this special 41CX just told me that he was wondering why he had the HEPAX manuals but no module anymore. After more than 30 years he forgot that it was built into the calculator. He was very happy that the module is still there, even if it's a bit hidden.

I took a few pictures. To avoid overloading this thread I just added the links:

• Picture #1
• Picture #2
• Picture #3
• Picture #4
• Picture #5
• Picture #6
• Picture #7
  

[KimH]

(03-25-2022 03:54 PM)Jurgen Keller Wrote:  

(03-23-2022 08:50 PM)KimH Wrote:  Hm…. Do you have a picture of the turbo-switch - maybe this is one i have made…..

Here we go


It looks like the red switch used für 41CYs, so maybe W&W did the modification. Did you work for them?

Thanks for the image, I made all mine inside the battery compartment, better esthetics. IMO…

No I didn’t work with/for W&W, I was more of a hobbyist modifying 41s and 71s and all mine were done in DK. Hundreds…. But all in DK. as Steen P. (who wrote the HEPAX) a Dane

[Garth Wilson]

EduCalc was selling a "turbo" modification in the 1980's, and I bought one. The switch might have been red, but I don't remember. However, the paper that came with the kit said it was not suitable for if you use HPIL or combined modules, both of which I used constantly, so I sent it back without installing it.

[rprosperi]

(03-25-2022 04:10 PM)Jurgen Keller Wrote:  I took a few pictures. To avoid overloading this thread I just added the links:

Ah... a HalfNut... tis a shame.... though I've heard some folks actually prefer them.

Nice photos Jurgen!