EEVblog #582  - HP41CV Teardown - Page 1
Forum section: electronics / general

author: DavidGoncalv
author_rank: Contributor
timestamp: February 17, 2014, 03:58:34 pm
content: Awesome! I love HP calculators. RPN kicks the quizzes' ass!Don't take the keyboard apart, but would it be possible to get the card reader mechanism and tear that down? That would be neat to see the strip go through and watch the data stream out.

author: FireBird
author_rank: Regular Contributor
timestamp: February 17, 2014, 04:41:05 pm
content: Dave, you've received a newer model. The older one had a separate processor board. Seeherefor a comparison (you need to scroll down to the bottom). The additional board is the time module of the CX model.

author: nathanpc
author_rank: Unknown
timestamp: February 17, 2014, 05:05:13 pm
content: Not worth damaging the calculator. Leave it intact.If anyone wants the video (since it still haven't been posted to the blog webpage):

author: 99tito99
author_rank: Regular Contributor
timestamp: February 17, 2014, 05:39:10 pm
content: Don't go any further.What's the purpose of the zig-zag trace next to the ASIC. Cheers, Mark

author: czdt8m
author_rank: Contributor
timestamp: February 17, 2014, 05:41:47 pm
content: Don't tear this one apart any further.One may pop up that is beyond repair. Worth waiting for that.

author: tszaboo
author_rank: Super Contributor
timestamp: February 17, 2014, 06:11:30 pm
content: It is working, keep it that way.

author: Bored@Work
author_rank: Super Contributor
timestamp: February 17, 2014, 07:02:08 pm
content: Didn't the submitter say this is a repaired/frankenstein unit assembled from several others?

author: hikariuk
author_rank: Unknown
timestamp: February 17, 2014, 07:18:25 pm
content: I'd vote for waiting for a dead one to turn up on eBay.

author: Maxlor
author_rank: Frequent Contributor
timestamp: February 17, 2014, 07:42:54 pm
content: I also say, don't destroy it.But I would like to see what the rest looks like. Surely, someone has a 41CV that's already broken that they can send you?

author: bktemp
author_rank: Super Contributor
timestamp: February 17, 2014, 07:55:13 pm
content: Interesting teardown, but I missed some comments on the odd pcb traces:There is one meander shaped trace, but it does not make any sense to me in such a low frequency design.One trace seems to be cut during design process but not removed.And another trace ends without any connection.Another interesting thing to note:The caps are 105°C rated. This is quite rare in such a low power device.

author: JoannaK
author_rank: Frequent Contributor
timestamp: February 17, 2014, 07:58:30 pm
content: Interesting machine.. Years back I took apart HP-28C model for repairs. Was real Pita to put back together since keyboard was fixed with those melted plastic rivets.So.. IMHO Dave, keep it as it is, no point ripping working classic apart.. I'm sure there will be broken ones around for full smashup.

author: DavidGoncalv
author_rank: Contributor
timestamp: February 17, 2014, 08:05:54 pm
content: This video made me pull out my HP-48G to run some of my favorite old programs. Alas!! Keys B-F no longer work! What will I do now? My programs!I bought it when I started college with summer work money, and man that 'infinite stack' and the stack operations and little time-saving programs I wrote saved me so much time in quizzes and finals. Once I walked out after 15 minutes, my class mates thought I had quit and would get the worst score but they were so wrong - they all did so poorly the professor felt bad and let them try again. I got a B and sat out that 2nd quiz.Cheated? No; if you can write a program to do the job against what might be thrown at you in a quiz, you've understood the problem and method of solution well enough. Also, I had a bad habit of forgetting every so often so I got to use a borrowed calc, a slide rule for giggles, or once just draw up a series of Smith chart plots and circle the solution location on the chart.

author: HP-ILnerd
author_rank: Frequent Contributor
timestamp: February 17, 2014, 08:26:43 pm
content: As my first post, let me just vote: Preserved It!I happen to own mint a C,CV, and CX plus a lot of HP-IL gear that they can run. Like a pair of 3468 multimetersand the 3421 data acquistion module, etc. You could make a whole series on how cool and inter-operable this stuffis.They really don't make 'em like this any more.

author: SeanB
author_rank: Super Contributor
timestamp: February 17, 2014, 08:44:48 pm
content: I have an old TI calculator that looks remarkably similar to the HP. Only issue is the keyboard is getting flaky, but other than that and some cosmetic damage it works fine. Looks like the HP battery packs would fit is as well.

author: Wytnucls
author_rank: Super Contributor
timestamp: February 17, 2014, 09:18:42 pm
content: I have a TI58 and HP41C. The battery packs are totally different, unfortunately.I also have two HP67s which can be completely dismantled, without destroying anything, if you're careful.

author: NickS
author_rank: Unknown
timestamp: February 17, 2014, 09:23:40 pm
content: Quote from: bktemp on February 17, 2014, 07:55:13 pmI noticed that too. Seems to link between 2 caps but it looks really bizarre.On the 'bottom' of the video there is also a cap, inductor, diode combo. Surely it doesn't have a switch mode regulator built in to the chip?

author: moemoe
author_rank: Regular Contributor
timestamp: February 17, 2014, 09:30:38 pm
content: It's teardown…MONDAY?

author: hans
author_rank: Super Contributor
timestamp: February 17, 2014, 11:27:47 pm
content: I would leave it intact, as nice as it is now.With a bit of googling, one can find the other side of the PCB rather easily:http://www.keesvandersanden.nl/calculators/hp41cv_inside.phpAnd it's just a few dome buttons.

author: electronics man
author_rank: Frequent Contributor
timestamp: February 17, 2014, 11:37:46 pm
content: Quote from: moemoe on February 17, 2014, 09:30:38 pmits tuesday in australia

author: Macbeth
author_rank: Super Contributor
timestamp: February 17, 2014, 11:47:19 pm
content: Don't turn it on - TEAR IT APAAARRT! RIP IT TO BITS!Too many HP fanboyz. Casio is where it's at wit' da kool kidz in town. Casio fx-82 is 4 life. It haz a ENG key, you know for real engineers, not paper plazzy degree engines.Kill tha pretentious HP shit. Fo Real dood! fx-82 has an ENG key!Ok, I will put the crack pipe down now...

author: Maxlor
author_rank: Frequent Contributor
timestamp: February 18, 2014, 12:40:24 am
content: Quote from: Macbeth on February 17, 2014, 11:47:19 pmThe HP-35s hastwoENG keys!

author: moemoe
author_rank: Regular Contributor
timestamp: February 18, 2014, 08:05:47 am
content: Quote from: electronics man on February 17, 2014, 11:37:46 pmI referred to youtube saying 'Published on 17 Feb 2014' even when country is set to Australia. But I wondered if I can't get it more accurate, so I digged into the yt rss feed:Code:[…]<pubDate>Mon, 17 Feb 2014 14:39:07 +0000</pubDate><atom:updated>2014-02-18T07:47:01.000Z</atom:updated><category domain='http://schemas.google.com/g/2005#kind'>http://gdata.youtube.com/schemas/2007#video</category><title>EEVblog #582 - HP41CV Calculator Teardown</title>[…]And Sidney is UTC+11 => Mon, 17 Feb 2014 14:39:07+0000 becomes Tue, 18 Feb 2014 01:39:07+1100 and you're right, but only technically (as the 'felt day' turns over with sleep').

author: Kjelt
author_rank: Super Contributor
timestamp: February 18, 2014, 08:14:18 am
content: Quote from: DavidGoncalv on February 17, 2014, 08:05:54 pmHmmm the 48 was not allowed in our courses since some smart ass had developed a program to communicate with ir to share the answers to other 48 owners. In your definition of cheating that would also be allowedI still use mine on a weekly basis but mostly for standard calculations.

author: EEVblog
author_rank: Unknown
timestamp: February 18, 2014, 08:40:15 am
content: Quote from: moemoe on February 18, 2014, 08:05:47 amFor those who really care, I uploaded this Monday night about 11pm or something and went to bed, it was a several hour upload. I forgot to set to Private, so it got released as soon as it was uploaded.

author: lewis
author_rank: Frequent Contributor
timestamp: February 18, 2014, 09:20:34 am
content: Quote from: moemoe on February 18, 2014, 08:05:47 amNowthat'scommitment

author: moemoe
author_rank: Regular Contributor
timestamp: February 18, 2014, 09:54:58 am
content: Quote from: lewis on February 18, 2014, 09:20:34 amThat's the legendary "german gründlichkeit"But to return to the original question: No, dave, don't tear it apart further. There is not much of interest on the other side:http://www.keesvandersanden.nl/calculators/hp41cv_inside.php

author: smashIt
author_rank: Contributor
timestamp: February 18, 2014, 10:16:18 am
content: Quote from: Macbeth on February 17, 2014, 11:47:19 pmPHA!ti30 is best calculator evaaaaaaaaaaa

author: EEVblog
author_rank: Unknown
timestamp: February 18, 2014, 10:19:45 am
content: Quote from: smashIt on February 18, 2014, 10:16:18 amThe Casio FX61F rules. It has dedicated electronics buttons!

author: RupertGo
author_rank: Regular Contributor
timestamp: February 18, 2014, 10:42:40 am
content: Don't take it apart any further - what would we see?But a couple of questions. Where does the processor get its clock from? I didn't see any resonator or crystal on the board. Wasn't that inductor, was it? Bit chunky.Also, at 17:00 and thereabouts during the close-up of the display connections, there are two fat PCB fingers that veer towards each other and end in what you'd expect to be vias - but aren't. What's that about? It almost looks like a spark gap, but I'm having a hard time believing that.You could work out more about the display interface with a bit of scoping. That might be interesting: reverse-engineering interface protocols is a bit of an art in itself, and can only get more so as the global stock of under-documented vintage digital kit grows! And you don't have to saw off the heat pillars...R

author: moemoe
author_rank: Regular Contributor
timestamp: February 18, 2014, 10:48:57 am
content: Quote from: EEVblog on February 18, 2014, 10:19:45 amMy vintage calculator also has electronics 'buttons'

author: DavidGoncalv
author_rank: Contributor
timestamp: February 18, 2014, 11:04:35 am
content: Has no stack!

author: moemoe
author_rank: Regular Contributor
timestamp: February 18, 2014, 11:47:54 am
content: Quote from: DavidGoncalv on February 18, 2014, 11:04:35 amJust forgot to take a picture of it:http://commons.wikimedia.org/wiki/File:PostItNotePad.JPG

author: DavidGoncalv
author_rank: Contributor
timestamp: February 18, 2014, 12:10:46 pm
content: Nice!

author: robrenz
author_rank: Super Contributor
timestamp: February 18, 2014, 12:19:01 pm
content: Don't take it apart, that would be a real shame. There is nothing on the other side that interesting to warrant killing a functioning piece of calculator history.

author: FireBird
author_rank: Regular Contributor
timestamp: February 18, 2014, 12:37:28 pm
content: Quote from: RupertGo on February 18, 2014, 10:42:40 amThe display is connected to the same bus as any other module/peripheral device. It is a 56 bit serial bus, where ROM address (16 bit) and ROM data (10 bit) is transmitted on one line, RAM data (56 bit) on another line. In addition, there are 2 clock and some other control lines. The LCD acts like a RAM, which means that it monitors the opcodes coming from ROMs and if the right ones passes by, it will read the data from the data bus.

author: BMac
author_rank: Contributor
timestamp: February 18, 2014, 01:20:09 pm
content: Yeah I agree, nothing of interest on the other side of that board to warrant destroying such a beauty!BMac

author: RupertGo
author_rank: Regular Contributor
timestamp: February 18, 2014, 02:38:03 pm
content: Thanks, Firebird! Does the display look for opcodes or addresses, or are they combined?Something like the HP calculator is well documented anyway, but I still think it would be fun to see Dave do a bit of protocol analysis. One of the more engaging aspects of the fault-finding and fundamentals videos is actually using all that lovely test equipment, so a live teardown appeals a lot...(happy thoughts of a live teardown on a 5kW VHF amplifier final...)

author: FireBird
author_rank: Regular Contributor
timestamp: February 18, 2014, 02:43:00 pm
content: Just for the opcodes because RAM and ROM address space is separated. These special opcodes are NOPs to the CPU but trigger some action in the peripherals.

author: Kompost
author_rank: Contributor
timestamp: February 18, 2014, 04:25:51 pm
content: There's no way around it, it's time to go in Mike's footsteps and get yourself an x-ray machine

author: Wytnucls
author_rank: Super Contributor
timestamp: February 18, 2014, 06:19:45 pm
content: This is the board of my 41C, serial 2213S44694. Bought in the eighties, if I recall properly.

author: RadioGeek
author_rank: Newbie
timestamp: February 18, 2014, 06:35:45 pm
content: Hey Dave, great tear down, but don't go any further. Would be a shame to tear up that classic!

author: TheWelly888
author_rank: Frequent Contributor
timestamp: February 18, 2014, 07:53:26 pm
content: Another one here saying, don't tear the board out! As long as the calculator is working, it's worth keeping.It's not worth taking a calculator fully apart as the keypad side of the board is quite boring. Though I once took my Casio FX100c apart out of curiosity, yawned at the keypad then re-assembled the keys. A few days later, my Physics teacher borrowed my calculator to show me the result of something and he could not understand why he was getting a nonsense answer until I realised I put the + and - keys the wrong way round!

author: (In)Sanity
author_rank: Regular Contributor
timestamp: February 18, 2014, 08:45:32 pm
content: Don't take it apart, turn it on.....and use it.

author: rjk5378
author_rank: Contributor
timestamp: February 19, 2014, 01:12:42 am
content: I vote NO!! Don't destroy it. However, it should not be too much problem to locate and acquire a non-working or "for parts only" model that you could tear up. <g>I'm the proud owner of an HP-41CX (that I still use). I had an HP-41 (with extra memory modules) from 1980 until 1994 when I absent-mindedly left it in a hotel room. The engineering and design of the calculator itself was, of course, a thing of true beauty. But also impressive was the documentation. The 41-CX had, in addition to the quick start guide, a two-volume manual spanning nearly 400 pages. Everything was laid out clearly. Not only operation of the unit, but the programming as well. One who had no computer programming experience could, by learning to use this calculator with that manual, get a very good foundation in programming concepts.My office at the time had the competing high-end calculator made by Texas Instruments. I can't remember the model number, but in order to get alphanumeric on it, you had to plug it into a larger units (approximately the size of a small portable typewriter) and it would print the information on a paper tape roll. Not just the results, but the interactive alphanumeric prompts, etc., as well. But without that extra unit, you had to rely just on the numbers in the display (red LED's if I remember correctly). Still, to me that was impressive at the time, and I was thinking of buying one for myself. A colleague dissuaded me. He loaned me his HP-41 and manuals for a weekend and, as he predicted, by the time I came back on Monday morning, I was sold on the HP. Went out and bought one at lunch time that day, and never gave the TI model another thought!I still use my HP-41 today. It sits on or near my desk, and I grab it when I want to do quick calculations. I have newer calculators, but truth-be-told, I am all but helpless without Reverse Polish Notation. <g> Except for an occasional nostalgia fix, I don't run programs on it any more, basically because it is slow. The kinds of things I sued to use the HP-41 to solve, that would in some cases take the better part of a minute and occasionally longer, can usually be had instantaneously today with the single click of a mouse on some web site. But I am nevertheless still in awe of the accomplishment that was this calculator.-- Bob, KY3R

author: rjk5378
author_rank: Contributor
timestamp: February 19, 2014, 01:22:36 am
content: Quote from: moemoe on February 18, 2014, 11:47:54 amLOL. I think you got your stack from the same place where they sell DaveCAD. <g>

author: calexanian
author_rank: Super Contributor
timestamp: February 19, 2014, 01:26:43 am
content: I also vote to leave it be. I would be more interested in seeing what the most complicated program it could run and how long it would take to arrive at the solution.

author: HP-ILnerd
author_rank: Frequent Contributor
timestamp: February 19, 2014, 02:55:45 am
content: That could actually be a while. One thing it isn't, is particularly fast. What it is, isflexible. The programing language "Forty One CAlculator Language" (FOCAL) is amazingly expressive for something runs on a calculator. It's capable of both indirect addressing and indirect execution, allowing you (in effect) to construct arrays or implement jump tables. Plus, via the User key, it's set up so you can re-define almost every key on the keyboard to execute a program or subroutine simply by assigning it to a key. If you have the Extended Functions module, or a 41-CX you can have aprogramreassign the keys, allowing you to configure the whole calculator for whatever it is you are doing. If you are an undisciplined programmer, you could make a horrid mess of spaghetti-code, but that said, it's nearly impossible to lock up the machine with anything in its instruction set. It's "synthetic" programming capabilities are a different matter. That lets you get at functions that were not for user use, and are dangerous to use casually.Other fun peripherals:The Time Module: Created at NASA's behest, this allows you to have programmable alarms that put the calculator to sleep, wake up at a predetermined interval, do something, then according to conditions set another alarm to do it (or something else) again, etc. There's one guy on one of the calculator forums who reports a 41 running an HP3421 data acquistion module to operate lawn sprinklers. The 3421 has a 5 1/2 digit multimeter built in, so you could (say) periodically (via the time module) measure sunlight with a photocell and turn on the sprinklers (it has relays built in) when it was too sunny.The applications are really limited by your imagination...and it's pokey clock speed.Excellent resource:http://www.hp41.org/Intro.cfmIf you have an iPhone, there is a phenomenal 41CX emulator available for it. I've written programs on that, had it email them to myself, made barcodes, read them into a real 41 via the barcode wand.

author: senso
author_rank: Frequent Contributor
timestamp: February 19, 2014, 03:27:01 am
content: Whats inside that MATH card?

author: HP-ILnerd
author_rank: Frequent Contributor
timestamp: February 19, 2014, 03:37:44 am
content: From the manual:Matrix operations,Solution to f(x)=0 on an intervalPolynomial solutions/evaluationNumerical integration,Differential equationsFourier seriesComplex operationsHyperbolicsTriangle solutionsCoordinate transformations (2 and 3d)

author: senso
author_rank: Frequent Contributor
timestamp: February 19, 2014, 03:50:18 am
content: Its like an expansion ROM filled with programs?

author: HP-ILnerd
author_rank: Frequent Contributor
timestamp: February 19, 2014, 04:04:57 am
content: In the case of the Math pac, yes. Programs. Sometimes the modules just add functions in hardware. There are even custom ROMS that were made if they were ordered in sufficient quantity (min was 5000). It may speak to the nature of the era when these were made that there was a Nuclear Weapons Air Burst Effects module made.

author: phamuc
author_rank: Contributor
timestamp: February 20, 2014, 12:03:31 am
content: For all that love HP calculators.You can get your free official HP calculator (Emulator).You have your choice of 10S, 300S, 15C, 35S, all with Full manuals in the help function!http://www.hp.com/sbso/product/calculators-emulators/scientific-calculator-emulator.htmlMy favorite is the 15C, its look and feel (OK the feel is psychology, I own a real 15C) is incredibly!I wish there was also a 16C Emulator.The only thing that sucks with these calculators, is you can't do a tear down of them.But you should NEVER do a tear down of a HP!and I hope Dave does NOT tear down (break) the HP41CV! Dave, I vote NO!!!Save the HP41CV! Long live the HP41CV!-Paul

author: johanan
author_rank: Newbie
timestamp: February 21, 2014, 12:50:38 pm
content: Don't kill it. I am almost sure there is nothing but the lcd display at the bottom.

author: electronics man
author_rank: Frequent Contributor
timestamp: February 21, 2014, 06:18:06 pm
content: Dave dont go any further it would be terable to kill something like that, find a dead one and then rip that one apart.

author: HP-ILnerd
author_rank: Frequent Contributor
timestamp: February 22, 2014, 12:57:02 am
content: Dave,A dead one might be interesting in and of itself, sincewhythey are usually dead is a good lesson on hownotto store your electronics: You will see often see used or even possibly unused ones on ebay where someone left the batteries in for years. Since the 41 draws while it's off, I've seen tons of sad looking units that have had their battery contacts eaten to green powder. Some of those get broken down and sold for parts.If anyone is looking to get a (good) one, makesurethey show battery contacts, and make sure they show it on, close-up on the display, make sure they mentionthe state of the keys. There are a few US sellers I'm comfortable with, and I have no idea where they keep turning up nice new specimens, but they do. Case and manuals are also helpful.The original HP-41 manual is the only manual I ever actually read cover to cover, and is a model of how a good manual should be written. There's copies of all the manuals for nearly everything at thehttp://www.hp41.org/website.[Edited for spelling. Good grief, need more coffee]

author: HeywoodFloyd
author_rank: Contributor
timestamp: February 23, 2014, 10:36:05 pm
content: Quote from: rjk5378 on February 19, 2014, 01:12:42 amThis sounds like the TI59 or 58:http://en.wikipedia.org/wiki/TI-59_/_TI-58. I am the proud(ish) owner of a TI-58C, still in its original box and with manuals, but it doesn't work any more. I actually used the thing myself at uni, and people were laughing at me for having a (by then) ancient calculator with LED display. I remember programming it, writing code for all its 480 bytesAnd I seem to remember it took it tens of seconds to do a complex square root...I also vote don't destroy the HP... IMHO one should not destroy stuff that works - not even to figure out how it works. And I like HP calculators. RPN - nice.

author: linux-works
author_rank: Super Contributor
timestamp: February 23, 2014, 10:51:24 pm
content: about 10 or 15 yrs ago, someone on the local usenet group (remember when they were still non-binary and non-spam?) wanted to give away a free hp41 that was non-working. I took him up on the offer.here is my flicker shoot of my repair:http://www.flickr.com/search/?details=1&w=47907743@N00&q=hp41the motor in the card reader was gummy (of course). and the wires to the lcd (elastomer) was bad so I bit the bullet and hard wired it with kynar. works fine and is more reliable now than with the rubber baby buggy bumpersI never use the 41, though. I bought a used hp25 which I like better, for some odd reason.

author: linux-works
author_rank: Super Contributor
timestamp: February 23, 2014, 10:55:13 pm
content: Quote from: TheWelly888 on February 18, 2014, 07:53:26 pmlol.reminds me of the steven wright joke:I bought a new phone though. I didn't have much money so I had to buy an irregular phone -- it had no number 5 on it. I saw a close friend of mine the other day... He said, "Steven, why haven't you called me?" I said, "I can't call everyone I want. My new phone has no five on it." He said, "How long have you had it?" I said, "I don't know... My calendar has no sevens on it."

author: SeanB
author_rank: Super Contributor
timestamp: February 24, 2014, 10:31:33 pm
content: I have 2 TI58C I bought on auction years ago. Dead ( really dead on the one and growing blue green fuzz all over, missing on the other) and no power supplies either, and cosmetic damage. Cleaned them up a little and bodged in a simple 4V8 zener diode as a battery replacement. Interesting way they stacked chips in them. think the memory capacitor is very dead now though. Must pull the photos off the camera and post them up.

author: rjk5378
author_rank: Contributor
timestamp: February 25, 2014, 12:41:20 am
content: Quote from: linux-works on February 23, 2014, 10:55:13 pm

author: SeanB
author_rank: Super Contributor
timestamp: February 27, 2014, 06:51:33 pm
content: Well, opened it up and took a few photos. Interesting in how they stacked the assorted chips to increase density.

author: HP-ILnerd
author_rank: Frequent Contributor
timestamp: February 27, 2014, 11:35:30 pm
content: Linux-works: Nice job fixing those, and spectacular photos! Amazing how no one anywhere seemed to realized what would happen to the gummy wheels over time. I have an HP-97 that works perfectly (cosmetically fine, too) but needs to have its gummy wheel replaced. It's on the list of things to do when I finish up my new bench...SeanB: How much of that main board is factory? Also, is that hot glue on the display?

author: Wytnucls
author_rank: Super Contributor
timestamp: February 28, 2014, 12:09:59 am
content: My TI 58C is much different inside. It is original, apart from the battery contact springs, which corroded a long time ago.The TI quality is very inferior to the HP workmanship.No stacked chips in this one.

author: SeanB
author_rank: Super Contributor
timestamp: February 28, 2014, 04:19:18 am
content: Only bodges are the epoxy on the cracked display on the front, and the zener diodes and capacitors replacing the battery clips which rotted away from the battery failing. The display has a cover to hide the crazing and scratches, must look to replace it or polish it, but it does not worry me. All the stacked chips and such are original, this is a very old unit, probably was made when I was still in school. It has a slightly bouncy keyboard, but still does all that it needs to.

author: Hydrawerk
author_rank: Super Contributor
timestamp: March 30, 2014, 02:24:53 pm
content: I have one, too. But I do not like RPN.

author: SeanB
author_rank: Super Contributor
timestamp: March 30, 2014, 02:39:34 pm
content: You need to dust it......

author: sa-penguin
author_rank: Newbie
timestamp: August 11, 2014, 06:11:37 am
content: This is now considered an old thread, but I just joined in order to say:"Don't pull the old HP-41 apart, unless you can GUARANTEE you can get it together again".If anything, this should be considered an exercise in quality manufacturing: using modern assembly techniques, is it possible to make a custom keypad to this quality level?Seriously, there are calculator enthusiasts who re-purpose the HP-30b into the WP-34S.They are trying to make a whole calculator from scratch (WP-43S) but it's slow progress.Some insight into how to make a keypad, as good as the one on this 41 model, would be appreciated.