I have a 20 year old, 6 zone Rainbird ESP controller that was behaving erratically. One of the symptoms was the display would not always show when I set the selector knob in 4 of the 6 zones. I wanted to adjust the length of sprinkling time.
I called Rainbird who told me due to age it will behave that way and its time to replace it. But since I don't give up easy, I wondered if the contact of the selector switch may just have some build up and were not making contact.
So after unplugging the power supply I pulled the knob out and popped the cover off exposing the board and the selector switch. I blew compressed air all over the unit to remove any possible dust and was going to spray the sw with contact cleaner and blow it some more. I was out of contact cleaner so I focused on the switch with compressed air a few more times.
Put the covers and knob back, plugged it back and Voila!!! Works!!!