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HP41CX tragedy strikes
01-28-2014, 01:11 AM
Post: #1
HP41CX tragedy strikes
I *had* a perfectly good working HP41CX that just had some minor issues in the battery compartment which I previously had fixed with a strategic piece of tinfoil.

Unfortunately my cat only understands algebraic entry, and in his frustration of trying to use RPN he knocked the calculator to the floor. (At least that what I surmise happened from the other room--I heard a crash, and walked into the room to see the cat on the chair and the HP on the floor.) It only fell about two feet, but now will not power on. No visible external damage, which includes the glass in the LCD. My first thought was that the tinfoil bridging the two corroded connectors on the battery was displaced, but in repeatedly popping the battery compartment and re-shifting the tinfoil, that is not seeming to be the problem. It looks like that minor drop has killed my 41CX.

It's not at all obvious how to disassemble the case. Before I crack it open and ruin my vintage calculator, is there anything that anyone has to suggest on how to disassemble it? If this is a common problem, any idea what type of internal damage I should look for? Any other good suggestion for something to try before I attempt a potentially dangerous repair?
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01-28-2014, 01:24 AM
Post: #2
RE: HP41CX tragedy strikes
They are relatively easy to open there are screws under the for rubber pads. One thing that may have happened to it in its fall is one of the posts that the screws go into may have broken. If this is a full nut CX there are two places where connection are made by the pressure of the screw holding the two halves together. If you place it on a table top and apply pressure to the top does it move a bit? If so try holding down the top like that with batteries installed and see if it will show some signs of life. If you go to "Repairs & Batteries" on the front page you will find some hints about fixing a 41.
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01-28-2014, 03:15 AM
Post: #3
RE: HP41CX tragedy strikes
A few times, including after very minor falls, I've had the problem with my halfnut cx that it won't power up. I always lay it down very gently now because of this, and the problem shows up a couple of times a year. I've never looked at the insides, but the power control seems to be on the same bridge board with the built-in time and date module, and the connections to it are not the best anymore. I just bang the side of the calc on the heel of my hand, and it it works again. I have to reset the time and date, but the other memory is unaffected.

http://WilsonMinesCo.com (Lots of HP-41 links at the bottom of the links page, http://wilsonminesco.com/links.html )
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01-28-2014, 03:51 AM
Post: #4
RE: HP41CX tragedy strikes
Thanks very much guys. I read through the repair tips on the main page, and both of your experiences. Pressing the calc together doesn't seem to work, but I am pretty sure that the case closure and/or disconnected ribbon is the issue. Without too much force, I can partially separate the case on one side about 1.5 mm or so. This seems a pretty clear indicator that one of the screw posts is broken.

I'm going to disassemble and try to repair it (just not tonight). I'll let you know if I'm successful or not.
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01-28-2014, 03:56 AM
Post: #5
RE: HP41CX tragedy strikes
100% guarantee that it is a compromised screw post front shell / screw back shell problem. Be it a suddenly loosened screw, cracked screw posts or separated screw post.

Check out this article and then search for "cracked hp41c screw posts" and see where that takes you.

Screw post article

Geoff

Do not tighten screws until you determine if the posts or shell halves are cracked!

Do not over tighten screws.

The module plugs and the battery foil are mounted to the same block and require a compression fit to the keyboard PCA. Otherwise dead or buggy hp 41c.
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