Repair: TI 58C

[Bicurico]

Hi,

I was at a flea market today and picked up a TI 58C. It came with charger and case and looked not too bad. The seller told me the calculator was not working, so at least he was honest.

I paid a ridiculous 5 Euro, which I though was worth it even if the calculator was beyond repair.

I expected the battery to have leaked and it was confirmed right away.

I gave the PCB some cleaning and connected 3.6VDC from my power supply and saw the "0" pop up. But none of the keys were working, so I investigated further.

Upon fully removing the PCB from the case I saw why the keyboard was not working: the leaked fluids had corroded the upper 3 rows of contact plates plus the centre wires. I expect the keyboard to be beyond repair, at least I wouldn't know where to get the metallic stripes with the cone shape that form the key contacts. Also, it seems pretty impossible to replace the contact wires.

So my question is: does anyone have some tips and tricks on how to repair the keyboard?

The calculator might suffer from bad RAM, which seems to be normal when the user tries to run the calculator with the power supply but without the battery pack in place.

If the keyboard is not repairable, then I guess it is not worth trying to repair the remaining PCB. This is a shame, though, as the screen is working beautifully and the PCB seems OK, as well as the case itself. I will try to post some pictures later on.

Cheers,
Vitor

[fzabkar]

Could we see some photos?

This TI calculator has snap domes under each key:

https://goughlui.com/2019/10/13/tech-flashback-repair-texas-instruments-sr-56-programmable-calculator/

[Bicurico]

This site has a wonderful repair documentation and some pictures:  https://www.hpmuseum.org/forum/thread-2334.html

The snap domes (didn't know the correct name for that) are seen here:



They form several rows and each row is like a stripe of snap cones.

They are held together by tape and snap over vertically laid out wires (which in my case are corroded, as well).

I will attach pictures in a couple of days, as I won't be home.

Regards,
Vitor