I would like to buy a synth module for my 9C but am concerned with the quality of the rotary switches. Is there anything in the circuit design that checks for an open switch? Like the kind you get when the switch gets a few years old? And the actual frequency you dialed does not agree with the indicator?

Bob

If a rotary switch is open, it won't transmit. If you're altering channels so much that you're wearing out the switches every year or two, then you'd also be sending in the system for checkups and the switches could be checked/replaced as needed.