After checking everything that you all suggested (motor, lid switch, coupler, blockage, brake, transmission, etc.) I decided to put the whole thing back together and start the troubleshooting anew, with an eye more towards electrical. Well, it seems to run perfectly again. One thing though... since so much time elapsed between tearing it down to re-assembly, I ended up w/ 2 small (5/8" x #8 or #10, maybe) sheet metal screws left over, and no recollection of where they belong. The machine has run through bout 4 or 5 full cycles and nothing has flown across the room... yet. Any fresh thoughts on either what the problem may have been, or will be again... or where those 2 screws go?