Thank you so much, Alan! I was not prepared for how insanely complicated the mechanism is, and how vague the manual is (like a lot of professional workshop manuals, I know). It assumes you know a lot about the technical names, locations, and functions of the components before you even open the book. I'm slowly figuring out what/where things are by staring at the drawings, and then poking around the machine.
It does seem logical that an electrical component between the search unit and the record magazine has suddenly dropped out, but since it was working before, and I didn't really "do anything" except take it the whole thing out, and then put it back into the cabinet, I was having trouble figuring out where to even start. So thanks for the suggestions. Also, in going back and thinking about what I touched in the process, I remembered that I did absentmindedly reconnect the main connector to the search unit with the power on, and heard what sounded like relays fire. Was that potentially damaging to something? Really appreciate your help, Alan! As technicians seem to be disappearing from Earth, the AMI Rowe community is very lucky to have you around.