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. ...
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...