I have a Rigid TP 1300 planer that started making an unusual noise as the blades/rollers stop. I removed the top and side cover, exposing the gearbox and chain drives. I wanted to jog the action to see if anything looks unusual but when I jog the switch on and back off, there is a hum but no movement of the mechanism. Yes, I know to be cautious when the cover is off, and unplug it to do anything more than observe. My question is whether there is an interlock of some sort that prevents the rollers/blades from moving when the cover is off?