Royal crosscut paper and cd shredder PX110MX repair?

My Royal PX110MX paper and cd shredder (2 months out of warranty) will not automatically shut off. I have thoroughly cleaned the cutting blades and even removed the protective housing around the blades to expose the circuitry, wiring and switch. Sometimes it will start up immediately upon turning it on, sometimes not. It started by itself in the middle of the night when I accidentally left it in the standby mode. It never shuts off after shredding paper whether it is one piece or 20 pieces unless I tap the reverse button while it running. Sometimes there is a second click when turn the unit on and that is a sure indication that the unit will run continuously.