Thank you for your reply and additional information. The most common cause of erratic DFC operation is the Start Voltages of the Roll and Pitch Trim Motors. A good Motor will begin to respond at around 2 Volts. Any voltage beyond 2.5 volts will cause erratic operation of the autopilot. The autopilot is also …
The DFC-90 requires Aircraft Power to be supplied to "A/P Disconnect" P1-17 and "Trim Interrupt " P2-14. If either input is missing the Autopilot will Disengage. The most common cause of DFC-90 problems is the connector mating into the old S-Tec 55x Tray. Insure that the unit is securely seated into the rack. …