HP41CV keyboard problem

[isanchez]

Hi,
I am repairing an HP41CV. There is no rust or corrosion inside.
I have replaced the zebra stripe (lower contacts) and one of the lower posts.
The upper contacts are original and look fine.
It turns on well and works fine, EXCEPT because the upper keyboard row does not respond at all.
( E+, 1/x, SQRT, LOG & LN). The rest is fine, all of them.
I would like to know where should I address my attention: to the lower contacts (zebra ) I suppose, or is ther any other issue I should also check?

Thanks and kind regards.

Happy Christmas for everybody!!!

Ignacio

[rocket.scientist]

Those keys are definitely all on the same ROW. According to the HP-41C/CV/CX Service Manual 00041-90472:

Quote:If there is a bad row or column, a key line is open or short-circuited (keyboard assembly, logic board, logic connector) or the CPU is bad.

I'd suspect the zebra connector first, especially having worked on a lower post.
1) Look for physical interface issues between board, zebra strip, and CPU board. Even a thin layer of wayward glue can cause an issue.
2) If you have a multi-meter look for conductivity between traces on the keyboard and the cpu board.
3) Try pressing carefully on the CPU board and zebra strip and see if that changes behavior.

Good luck!

(12-23-2024 01:11 PM)isanchez Wrote:  Hi,
I am repairing an HP41CV. There is no rust or corrosion inside.
I have replaced the zebra stripe (lower contacts) and one of the lower posts.
The upper contacts are original and look fine.
It turns on well and works fine, EXCEPT because the upper keyboard row does not respond at all.
( E+, 1/x, SQRT, LOG & LN). The rest is fine, all of them.
I would like to know where should I address my attention: to the lower contacts (zebra ) I suppose, or is ther any other issue I should also check?

Thanks and kind regards.

Happy Christmas for everybody!!!

Ignacio

[isanchez]

Hi,
Thanks a lot.. I would check the zebra contacts.
I can also replace the board and see if it solves the issue.

Kind regards

Ignacio

[isanchez]

Hi Rocket,

you were absolutely RIGHT! I have cleaned the contacts and replaced the zebra (the one I used was an old v.3 of Jose González) for his v.4 and voilá!!! works nice.
Thanks again!!!



regards,

Ignacio

[rocket.scientist]

Certainly. The folks on this forum have been so very helpful to me, it is nice to pass things on.

Enjoy your newest toy. Um - tool. :-)

Best of the Holiday Season to you and yours.

-Pat