I would test the encoder in service mode. If it's working, you might be looking at a new main board unfortunately. If it doesn't work, you might just have a bad sensor.
To test the sensor:
-Power on while holding the up, right, and down buttons
-Once it boots, scroll down to the, "Inspection" menu and hit enter
-Then scroll down to the, "Encoder" menu and hit enter.
-Then select the PF encoder option and hit enter
-Now have someone move the feed motor forward manually and watch the screen.
-If the number stays at 0000, the sensor is broken. If the value changes, it is probably good.
After that the only other thing is the main board as it's what controls the motor.