There is usually a fuse on the front face of the clock near the reset button.
You have to push the black knob in and rotate to get the fuse out.
This will kill power to the clock.
Good luck
Imperial Valet controllers are different than what you describe. Their circuitry did not keep the power transformer connected to line voltage, unless a zone was actually powered. Therefore, a fuse for its primary side wasn't really needed, and the Imperial Valet controller only has a circuit breaker for the 24-volt side of that transformer. All the controller motors run on line voltage, and as long as the controller is connected to power, the main timing motor is running.