Edit: Looked at schematics for a while. Look at the two diodes that rectify the 9v AC. Where the heck they're located, I'm honestly not sure. The manual is very vague about this. It'd be where the two fuses for the shaker motor are.
Edit edit: I'm pretty sure they're on the shaker motor board. What a weird setup.
Edit edit edit: Okay, last edit I promise. Yeah, you either need to change out the diodes, or one of the two fuses is blown. If you're not cool with soldering and the fuses are okay, you can buy a new shaker motor board from marco.