Finished recapping the Capstan Speed Control (forgot to take pictures, damn it!) and the -12V rail is restored. However, the capstan and take up motors still spin upon power on.
I was testing some transport functionality, so the machine was on for a few minutes and IC 3 on the pre-divider started smoking. It’s cracked, and I don’t know if that’s a fluke/wear, or a failure that caused it to overheat. Anyway, I’m not sure that has anything to do with the motors spinning.
Recap tally: PSU, all 3 motor control boards (suppression caps), transport, capstan speed control. The counter isn’t recapped, but I don’t think that could be it. It feeds (or gets a signal from) the transport, so maybe that’s why the motors are spinning? Maybe the motors’ transistors are gone? I guess that could be an easy test since one motor isn’t spinning, and they all use the same transistors.