72 CE Down, any ideas??

[HPC]

Our Polar 72CE went down again, I keep patching this thing as its a good backup. When the power is turned on the backgauge locks in position, will not move. Also, the knife will not come down. It has full power going to it, belts are fine, motor fires right up, fuses have all been checked, overload breakers all checked and not tripped. Can anyone think of anything else??