On the Royal Super the motor capacitor could be the problem.
Are you able to change it?
On the Crown Supermax you should unsolder the Varta Batterypack, it ist very old and will beginn to leak. You are very luck, till today it seems to be ok.
You can solder a new battery Holder for normal AA Batterys, but then you have to solder a blocking Diode, because in original it is a chargable battery pack. Or you could use 2 AA charagble Batterys in a Battery holder mounted outside.