Double Extended memory module HP41cx..


Call me slow, but can I find the 'how to' guide to installing two extended memory modules into one module or into the HP41cx itself.

I have spent quite some time searching through the site, and using google site search tool all to know avail. Lots of postings on the extended memory and double x memory but only side talk about the journal article at the museum and etc.

I am looking for the actual with photo how to on doubling up the x-memory module or better yet the article on installing the chips internally and lining them up on either side of the battery compartment.

The reason is I want to free up a port for a clonix41 module which will include a series of my programs as well as the CCD module and whatever else I can cram into it!

Cheers, Geoff

Edited: 15 Mar 2008, 7:54 p.m.


Go to the article
and open the attachment :-)


D**m, I thought I tried this and I KNOW I have seen the article.

Many thanks and I will give it a try. The other point would be, has anyone done this hardwired internally. If so pointers would be appreciated or I might just play this safe and leave it in the module.

Cheers, and thanks Geoff


If you can bear the pain, I would strongly recommend the modules vice modifying the 41CX. Here are some things to consider:

IMHO Pro's of the module approach:

  1. If you screw both XMEM's you're only out $100
  2. If you succeed and it is well done, you will have something worth MORE than $100. (Closer to $150)
  3. It can be transfered to another machine when needed.
  4. You run no risk of damaging the delicate posts on your 41cx by NOT opening the case (and you can test the module on a less valuable machine before plugging in to the nice cx!)
  1. If you mess up your 41CX you are out at least $200
  2. If you succeed and it is seamless, you will likely decrease the value of your CX. (decreased reliability in spite of increased capability)
  3. It can't be ported to another calculator.
  4. The chances go up significantly of breaking a post every time you open your 41 series to do upgrades/repairs.

Allen solved your problem much quicker and better...

FWIW, for doing it internally, maybe the first article mentioned (V8N1 p20-21) might give you some ideas. It has a picture showing two memory modules internally.




I have done these modifications several time. I combined two X-Memory modules into a "Double X-Memory Module" and I combined a X-Functions and a X-Memory to a "X-FUNC & X-MEM Module".

The work is really hard as the wires you can use are extremly fine and the short and will desolder during your work many times. I need about 90 minutes for a module.
Now I have about 6 Double-X Memory Modules. If you need one, drop me a mail.



Cool overlay! I once went through the trouble of reading all the PPC, CHUU, Datafile, etc journals that are available on the various DVD's and print out and sort the articles into themes. So I have a bunch of articles that are related to double/tripple modules, some of them from the old days talking about normal memory modules. Some of the maybe more relevant articles for your effort can be found at:

PPC V8N1 p20 - Installing modules inside the HP-41C
PPC V6N7 p24 - 24c Ram Mod
PPC V11N1 p28 - Procedure for Module Doubling/Tripling
PPC V13N7 p21 - Procedure for Module Doubling/Tripling
PPC V11 N5 p3 - The BUtchers Block - Part III
(part II is about adding another module to the HP-IL.
if can be found at V11 N4 p16.
part I, the introduction about the layout of modules etc
it can be found at V11N3 p 6.
Lastly, the author, David White, I believe, can be found here on the forum...

I also have one page, handwritten from W&W about how to build 'Two X-Memory modules'. Alas, it is in German and not part of any DVD afaik

Let me know if you do not have access to the PPC journals mentioned and I shall find a way to get them to you (fax, mail. No scanner in reach right now...) You can reach me via email here, just make sure that there is a HP-41 reference in the subject line, as there simply is too much spam covering that inbox (sorry Valentin for borrowing your trick, I hope you do not mind)

Cheers, Peter


Here are some internal pictures.. a little better than the hand drawings of what you may expect inside.


Thanks Allen and Peter for your direction and references.

Cheers, Geoff


microsoft word and formatting the font and size until it prints in scale to the overlay.

I then print on a sheet of clear adhesive backed inkjet paper by avery. Using a razor blade and steel ruler I slice each row and then place on the overlay.

Sure beats the Letraset I used back in the early 80's.



Double and triple module conversion isn't much of a challenge! :-)

In the olden days, before the 82170A quad memory module, a few adventurous people like Bob Edelen were making the equivalent out of four 82106A memory modules. In order to make four of them fit, they had to be filed down, and the inside of the plastic module housing alos had to be milled down. The difficulty with this was that in some modules the bond wires were too tall, so filing the module would cut them. Bond wires are typically 25 to 32 micron diameter. There was no practical way to repair them, so the module was ruined.

Edited: 16 Mar 2008, 3:19 p.m.


Everyone, thanks again for the help.

As of now I have 2 x memory sitting in my calc and need them for work so I have 2 spares on there way along with some empty modules already opened and waiting.

I will update all when they arrive and are completed.

Matthias Wehrli, thanks for your offer and if I mess up (hope not) I will be contacting you. If I do not mess up I will set the second two into a module and end up with one double xmemory per HP 41cx (my spare also).

I tried to email you but that function has been turned off during Peters spam check. I will try again later when it allows me back in.

Cheers, Geoff

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