41CX with Interesting Problem


I just obtained a halfnut CX that works great, except for one thing. The 'CLX' (left arrow) key doesn't work. What makes it interesting is that the key does work when doing a full reset. So "CLX-ON-release CLX" results in "MEMORY LOST," but pressing CLX after that doesn't clear the message. As far as I can tell, all the other keys are working. The calculator does seem reluctant to turn on from time to time.

Before I open it up, I thought I'd ask here to see if anyone had thoughts on that set of symptoms. Thanks for any help you can offer!


Does CLA (CLX in ALPHA mode) or SHIFT-CLX work at all?


I was going to say "NO" to both, but then I discovered that pressing SHIFT followed very rapidly by CLX works, both in alpha and normal mode. Pressing them simultaneously doesn't work, and any conscious delay beyond the shortest one I can manage won't work either.



any related awkward behavior in PRGM mode, too? I mean, does it clear program steps as it should do the `back step` procedure?

Is there any chance that it has any additional module inside? Have you tried CAT 2 and observe if there is any occurrence?

This is actually interesting... I hope you succeed having your CX back into normal operation.

Luiz (Brazil)

Edited: 29 July 2005, 11:30 a.m.


Yes, I thought it was interesting. 8)

Nothing unusual shows up in CAT 2. The machine came with an I/R module and a surveying module, but I've removed those. There was also a protected program in memory that went away when I reset the machine. I haven't asked the seller about that because he looks to be a surplus/second hand dealer with no other calculator stuff for sale. The machine came in a bundle of other machines from TI, Casio and Sharp. All that suggests the seller won't know anything specific about the machine.

The CLX key works the same in program mode. That is, pressing SHIFT-CLX in rapid succession enters "CLX" into the program. Pressing SHIFT, then SHIFT CLX rapidly deletes the current program line.

My theory is either that there there is internal corrosion that is affecting the CLX key press by itself due to increased resistance. In this scenario that resistence is overcome briefly by pressing the shift key. Or else there's a problem in the decoding of the key presses in the CPU. I guess it's also possible that it's the classic broken lower post problem. But pressing one or both keys forcefully doesn't seem to affect the behavior.

There's no sign of corrosion externally, but I sure hope I find some inside. There would be hope of fixing things in that case, whereas a bad CPU is probably the end of the line, since I don't have a spare halfnut CX. On the other hand, I find that I can reliably operate the key now that I have the hang of it. I think I'll make this my main 41 for a while. It has a scratch across the display too, which makes it less valuable for resale. My practice is to hold on to flawed but servicable equipment for my own use and sell the better quality stuff. I figure I add value through my selectivity in the base machine and the add-ons that way.

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