I have an EZ Cut CNC plasma table that has so far been a great machine....until yesterday. It gave me a code of XB to start. Now it does not seem to be reading any type of limit switch sensor. The gantry will start down the table coming to the "home" position and doesn't want to stop. It will grind the gears on the rack trying to move farther than what is allowed. Any ideas on how I can check the switch or where the sensor for this is located?