Rain Bird ESP-6 Sprinkler controller buttons no longer functioning—do I need a new controller?
If the membrane buttons are on the circuit board, a new one might fix
it.
On the other hand it's an electronic device that's 19 years old.
Assuming you can even get a replacement part, it will probably cost a
significant percentage of just replacing the whole thing with a new
unit (and typically the new unit will have a warranty period, while a
replacement board may not.) Go shopping for both ways and make up
your mind.
A third possibility would be to see if you see anything that you
might try when you search for "membrane keyboard repair" - I have not
sifted through the results, and I'm not going to link to any, but
there did seem to be a variety of options such as replacing the
unreliable things with reliable types of switches, and various
attempts at opening them up and cleaning them. I'd prefer replacement
(not a fan of the things, longevity-wise), which should be as easy as
wiring 4 switches into the place where the membrane switches connect.