I read on a forum that the shaker is activate by Sol.24 and Q.25 on A3 Driver board.
Only got Stargate schematic where nothing is link to Sol.24
Follow wires by colours to fuses panel next right to the tranformator...test them all (don't know the one is)
If new fuse burns, the motor could be HS
To test a DC motor put Ohmmeter and if you got 1 as a value with sound, it is HS, if you got a value under 1 it is good.
If it is HS you might look at Q25 on A3 board.