Wild_Bill wrote:

I might be tempted to try an external switch to find out what the circuit
requires for more predictable/reliable operation.

The rubbery buttons' pads are conductive, obviously, but rarely low ohms in
resistance. With a common momentary switch and a 1k (or 200, 470 etc) series
resistor, the unit may operate just fine.
Then check the resistance of the existing switch to see if it's near the
improvised resistance that works well.

The rubbery switches' conductive pads generally increase dramatically with
use. Looking at aged conductive pads, they often develop a glazed-looking
surface from being pressed repeatedly.

I often scuff them very lightly with very fine abrasive (approx 600 grit) or
one of those fiberglas pen scuffing tools, but very lightly.. just enough to
remove the glaze from the pad.
The resistance comes back down, and the conductive pads work fine until they
get glazed again.. many uses later (like keyboard keys, IR remote buttons
etc).


I used to repair Commodore 64 computers. The keyboards had the same
type of switches. I would clean them with Isopropyl alcohol, then wipe
them across a piece of cloth (like Denim) to remove the dead surface.
You could see how much was removed, because live surface didn't leave a
streak on the cloth.

--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.