HP 41CX "restoration"



looking for someone to restore my HP 41CX in quick turnaround time. it has sticky keys, cracked display window (lcd ok) and missing rubber feet. found someone on the net awhile back but can no longer locate them.
any suggestions? my unit works but i would like to get it fixed as i use it daily in my work. prices for decent used 41's are ridiculous or would simply purchase. any help would be greatly appreciated.

b. turner


Is a fullnut or halfnut?


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If the calculator is a "fullnut" then all you need to do is
get an HP41C from eBay and swap the circuitboard. Its a quite straightforward operation and can be done in about an hour.

HP41Cs (or even CVs) can be found on eBay at reasonable prices if you take your time.




to identify which one is yours, look at the image below:

This is an original MoHPC image.

I successfuly exchanged the case from both fullnut and halfnut with each other. If you cannot find a compatible case, it's possible to exchange but will take a lot more than one hour and will need some service.

The keyboard on each calculator must be removed, what means cutting plastic rivets out and settling the keyboard back in the other case somehow. If you are using a fullnut case and a halfnut circuit, some plastic rivets must be completely removed because the halfnut keyboard does not have all holes existing in the fullnut's keyboard. The opposite situation does not require this operation.

Look at the image below:

The board shown in the left is a halfnut's board, and the one in the right is a fullnut's. The black holes in the fullnut's image indicate which rivets must be removed in a fullnut's case when "receiving" a halfnut's board.

Hope this helps.

Luiz C. Vieira - Brazil

Edited: 22 June 2003, 12:40 a.m.



How do you fix the keyboard again?. What can be used to replace the plastic rivets?




Hi, Jon;

the fact is that I cut only the necessary out of the original rivets. I do not remove the "mushroom" completely, I cut around them. Then I use existing plastic slices (or styrene) and melt some of them back (not all) to settle the keyboard. What I use to melt the plastic is something that works for me: a 220Vac soldering iron (35 to 40 watts) connected to a 110Vac outlet. It heats the plastic enough so it melts but it's not hot enough to burn the plastic. You can also use a rectifying diode (my first experiences) in series with the soldering iron so it will take only half of the AC wave, and in this case you'll have about the same effect as connecting it to 110Vac. I gave up the diode because in one time its terminals touched each other and I did not see it, so one small plastic burnt out and I inadvertently smell the fumes. Believe me, not a good experience.

After this partial settling, I use a silicon-based glue in the remaining rivets. What makes me sad is that this technique gives good results, but is not 100% perfect. I'm sad to say that in at least two cases I did not get the best results. I reassembled some keyboards in Pioneers, Voyagers, Woodstocks, HP41 and two HP48. Spices have an extra advantage: no melted rivets at all. I also don't know what is the HP49 made of...

The HP41 is a particular case. I have a fullnut HP41C that has no refurbished rivets, the keyboard is solely maintained by the four case screws. I thought about the HP41 and it's a particular case: the keyboard is completely "pressed" by both cases. The two big screws (close to the LCD) lock the keyboard in place because of the BATT/IO assembly, and the two small screws must press the mainboard to the keyboard. The four screws lock both half cases together and the result is that the keyboard remains steady even if all rivets are loose.

I'd like to know what others are doing.

Best regards.

Luiz C. Vieira - Brazil

Edited: 22 June 2003, 4:58 p.m.


Hi Jon, guys;

I also remember (have no clue about who, when, how) someone mentioned one kind of glue that is sort of sealing, rubbered material when "dried". It seems to be perfect, but I have never used it and have no idea of what sort of stuff it is.

Maybe the one who posted about it will read this and add the identification.


Luiz C. Vieira - Brazil

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