The Robertson AP300DL (P/N 20191540) is an autopilot control head that interfaces with the vessel’s steering system and magnetic course detector to provide automated heading control. Common failure modes for this class of units include power‑supply instability, corrupted firmware or configuration data, defective relays/contacts in the steering output circuit, and loss of communication with the magnetic sensor or rudder angle indicator. Initial troubleshooting should verify that the unit receives its rated 12 V DC input (check fuse and regulator), inspect all connector pins for corrosion or loose contacts, and review any diagnostic LEDs or error codes displayed on the head panel. If power and wiring are sound, perform a firmware integrity check and test the steering output by simulating a rudder command to ensure the relay/solenoid is functioning.[oss-gpt-20b]