Watching operation the drum shaft/barrel turns around twice: the first run is extension of the food drum and the second rotates the drum to dispense the food. On the first rotation the plastic off the barrel goes past the switch quickly and does not trip the reverse of the motor. After dispensing the food as the barrel rotates in the fully extended position right before the home position it hits one of the risers on the barrel sleeve which slows the motor enough for the switch to be tripped reversing the motor, that is the clicking sound we hear as the drum gets close to the retraction position. I'd think over time the height of the riser will wear down and stop the switch from signalling the reversal of the motor.
After assembling the AFS seems to be working correctly, for now. I think the exact position of the circuit board - and the sensor attached to it, is the primary cause of the malfunction. Be careful when inserting the USB plug. The board is held in position by 4 guides and gap to the AFS body set by 4 posts. The only hing holding the board in place is a 2 sided sticky adhesive on the top, not screwed down. I think as the AFS is running the movement in the body/vibration and the tacky adhesive is allowing the board to move out of ideal position resulting the switch not being tripped to reverse the motor.
We'll see what happens over time now that I'm working properly again. What was happening was the drum would rotate multiple time and not retract in the correct location/ not good on the motor or gears. I'd fill it up and after a few days find the drum not in the correct position and empty - dumping a whole drum into my tank. Can you say massive over feeding and chemical spikes? For the money I'd think this would have been engineered and field tested a little better, worst Neptune product I've tried. Hopefully a next gen will be better designed and manufactured.