HP-41CX "Halfnut" Internals (image)



I am the proud new owner of an HP-41CX purchased on eBay. After receiving it, I noticed some parts rattling about inside - although it proved to be fully functional. As it was missing two rubber feet, and I was going to manufacture some new ones, I thought it worthwhile opening it to see about the rattling and to clean up a small amount of battery corrosion before gluing on the new feet.

It turns out there were a few plastic posts to do with the module/battery connector assembly that had broken off and I have now successfully glued them and reassembled the 41CX with no more rattling. It all works beautifully again. :-)

A few observations: I had the 41CX disassembled for about 18 hours, cleaned contacts, glued posts and so forth. Upon reassembly the memory contents, programs, registers and so on, were still fully intact - amazing! The date and time, however, were indeed reset. I was quite surprised that the capacitor managed to last that long!

I have never seen an image of the inside of a "Halfnut" 41 anywhere, so for anyone who's interested, I have put an image of the opened 41CX on my web-server (1280x960 at 215Kb). The CPU appears to be surface-mounted directly, rather that being on a separate (and much more complex) circuit board as was on the "Fullnut" ones. The red and black wires on the right lead to the piezo speaker which is taped to the other case half.


My question is, can anyone tell me what the beige circuit board with the foam strip is? Is this perhaps the Time/Ext-Functions/Ext-Memory module that is added to a 41CV? Or is that the actual CPU board and the surface mount IC visible underneath (with the "hp" logo) is just a support chip? Not important... I'm just curious...

I am really impressed with the 41CX. I briefly owned a 41CV in the mid-eighties before moving on to the 48SX/49G/49g+ but I am now much more impressed with the design of this calculator than I remember being back then. Don't get me wrong though... I am a huge fan of (most of) HP's RPL models too!

Mike Mander

Edited: 19 Jan 2004, 3:55 a.m.



The board (or maybe better bridge) is indeed the X in CX.
The black chip sticking out on the MB is the CPU ROM etc all in one chip.

Under the bridge (id you remove it) you will find the resonator circuit that drives the clock. at that's about it.

Hope this helps



Hi Kim,

Thanks for the info! HP sure did simplify things! Any idea if the operating power consumption is lower on the "Halfnut" models? I suspect it probably is...



I honestly don't remember anymore it's over 10 years ago I played with these (turbo in the hundreds), but I would assume you're right.


I have some 41CX machines that have kept their memory alive on the capacitor for over a month. CV's usually last a week or two. 41C units up to a week.

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