Auto-Feed
There can be many issues. It could be your auto-feed tach. See if the tach is responding. If the tach is okay, please check the auto-feed solenoid and see if it's getting voltage. If it's getting voltage the cartridge could be corroded and the solenoid is energizing however, the cartridge won't move back and forth. You can take a fine grit emory paper and clean it up. Before putting it back in use a very light oil like 3 in 1 and it should work just fine. Another thing I just thought of would be the speed sensor that reads the rpm's off of the fly wheel could be bad. Usually chippers read the rpm's off of the altenator or the speed sensor that goes through the clutch bell housing.
Hope this helps!
Dave
Global Equipment Exporters