HP-29c keyboard dead 2nd row problem

[Xavier A. (Brazil)]

Hello everybody,

Until today, my beloved HP-29c was behaving like a charm - I just entered in a 94 steps program a week ago, and made a lot of calculations with. Everything was okay.

Today I realized the 2nd row was not reacting at all. Neither x<>y, nor Rd, STO, RCL nor Sigma+, and even the 2nd & 3rd functions are like dead.

I shall open my HP next week-end. I searched the forum to find any message about this problem exactly, but in vain. I saw some old but precious advices about cleaning, I'll apply them. I read also something about HP-67 cicuitry, I think it could help.

What can it be?

Thank you for any advice!

P.-S.: just to add that my program contains instructions STO & RCL and the calc executes them correctly.

Edited: 11 July 2012, 9:33 p.m.

[Harald]

If you are lucky, it is just a bad contact from the keyboard to the main pcb.
Take it apart and check for corrosion on the contacts. Clean if necessary. Hopefully it should work after that.

Good luck!

[Xavier A. (Brazil)]

Thanks for answering, Harald. It should be what you told me (well, if I'm lucky); more news on Sunday.

Edited: 12 July 2012, 7:59 p.m.

[Xavier A. (Brazil)]

Bad news. It seems to be a keyboard issue, since my pgm was okay with a lot of STO, RCL, x<>y and Rd instructions.

I carefully cleaned the contacts, but the row is still not responding. Is there any other solution than find a keyboard replacement?

[Jim Johnson]

Hello Xavier: You may try to use a meter to check out your keyboard. If you look at the reverse side of the keyboard (pcb side)you'll see a row of plated through holes near the top/display end of the keyboard. The row for the affected 2nd row keys go to the plated through hole that I call #7 (3rd pcb plated hole from the right as looking at the keyboard from the reverse side). Either this pin has become loose on your main pcb or there could be some interconnect issue inside of the keyboard. The keyboard row pins are scanned through the 1820-1382 cathode driver IC. This connection goes to pin 20 on the 1820-1382. You can check the traces and the solder connection to this IC which should route back to the previously mentioned pcb plated hole #7. I have a diagram of the keyboard that may help explain this. But I'm having some trouble using Flickr and linking the image into the HP Forum messages.

[Xavier A. (Brazil)]

Thank you, Jim.

Actually after my last message I have tried to press smoothly the keyboard two or three more times, and, you know what? the 29 is now working normally.

But for sure there is something wrong into the keyboard, or at the PCB connections (but I think it's in the kb). I shall do what you adviced, and also clean the kb in a vinager-water 50% solution.

Edited: 17 July 2012, 7:10 a.m. after one or more responses were posted

[Xavier A. (Brazil)]

Jim, there is no need to send me your schematics, since everybody can find it here or there. Thank you (and you know why!)!

Edited: 17 July 2012, 9:22 a.m.