Rudys mouth would not open but it would close, you could hear it pulsing in test after it initially closed. I checked the 2 drivers and pre-drivers and the transistors on the high current board right before the motor. I suspected at this point the LM 339 chip, socketed and replaced. No go. Upon tracing it turned out to be the ground wire from the high current driver board to the main driver board (bad IDC connection). On J1 of the high current driver there is +12, ground, and 2 inputs coming from 2 different drivers. The output is + and - to the motor. Here's my question, if the ground was missing how could the mouth close? On the schematic, one driver is labeled (driver up down) the other driver says (enable) And, I'm sure the comparator chip has everything to do with flopping the + & - to the motor, any insight on how this circuit works would be interesting.