William suggested the logic probe. We also have the privilege of being able to examine a full CPU board diagram from the identical Addams family (no circuit diagram in the Getaway docs).

Pin 16 is the relevant one for switch column 3. The logic probe output on Pin 16 sounds good, and similar to its neighbors. However testing it all the way to jumper J206, we find the corresponding pin 3 input sounds different from all the good ones. This makes it likely that there is a bad component in the resistors / capacitors on the board (R69 or C13).

Note: for using the logic probe, you will find on the power board there is ground at GND and 5 volts at test point TP2