I've pulled the base of the C8 apart following the instructions on
this site .
The only change I made was instead of removing the 5/8 nut on the bottom of the base unit, I removed the circlip from the top. (the nut was too tight to easily remove)
This allows the main base piece, with the motors to detach.
I applied power (
CAREFULLY! that's 240V exposed) and watched the gears - sound but no movement..
Looking at the top case of the motor, there is an inspection hole that shows the motor is turning.
Looks like a gearbox problem. If you hold the gear on the motor, there is no indication that it's trying to turn. There's a fair bit of backlash too.
Next step - pull off one of the motors and see if the gearbox can be accessed.