During a carve the carving bit suddenly dug a hole and stopped with a 313 z stall error. I couldn't start anything (measure, carve etc) afterward because as soon as I hit a button I would get z stall immediatly. After checking different things I found the encoder disk (I guess thats what you call it-almost clear disk on the inside back of the z motor) had separated from the spindle and wasn't spinning. Put a little super glue with a small paint brush on it, pushed it together, and works like a charm now. Hope this helps someone else.