Auto-Throttle system completely inop. No movement during return-to-service test. "A/T ENG CAM" failures reported for all three engines. Tried servo, no help. Removed servo, manually drove gearbox and had spline freely spinning and NO throttle movement. With servo held in hand, ran RTS test again, servo spline drove in both directions. (All FCC electrical inputs and servo outputs valid and operational.) Gearbox bad. No throttle movement was picked up by FCC's because none of the cam position switches changed state after servo was commanded to move throttles.
MD-10-10 ATA 22-30 Auto-Throttle Troubleshooting
Maintenance Manual 22-31-03-4