HP 31E buttons not responding

[Adam Vaughn]

Hello everyone. I recently picked up a HP 31E calculator. At first, everything seemed fine. However, it seems to have developed an issue with the 8, 5, and 2 keys. They seem to have become highly intermittent, taking many button presses to work. When they do work, there seems to be a far higher amount of 'key bounce' than with any of the other keys, causing lots of repeating. At first, I thought the keys might just be in need of cleaning, but the fact that they're in the same vertical row makes me wonder (though the decimal key seems unaffected). Any ideas on how I might be able to solve this issue? Thanks in advance!

[Michael de Estrada]

Unfortunately, the circuit trace may be cracked on that keyboard button set, and is not repairable. If it were a normal pcb, you could repair the circuit with solder, but the Spice board will be ruined if you do this. I had several go bad on me and had to use donor boards from other Spices. The good thing is that the circuit board is interchangeable among all the Spice models.

[Eric Smith]

You could try a silver conductive ink pen, such as a Circuitworks CW2200MTP. There are also nickel conductive ink pens, which are less expensive, but I think the silver ones would be more likely to provide a satisfactory repair.

I've also used conductive silver-filled epoxy for some repair jobs. It's more expensive yet, and less well-suited for PCB repair.

[Michael de Estrada]

Have you repaired Spice keyboards this way. The problem sometimes is on the snap dome side, and unless the ink pen material is very flexible, the repair is not likely to last.

[Adam Vaughn]

What would I be looking for with regards to breaks? I'm hoping to not have this lovely calculator rendered as a fancy-looking paperweight...

[Michael de Estrada]

It's very hard to see. You need to simply check for continuity with an ohmmeter. Sometimes the film with the snap domes separates from the circuit board where it is connected, losing continuity at that point. Perhaps it could be riveted together to fix it. I tried solder, which just ruined it. You could ask a pro like fixthatcalc if it can be repaired.

Edited: 12 June 2011, 10:58 a.m.