As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF RUDDER STARTED CYCLING LT TO RT. RUDDER CYCLE BECAME MORE VIOLENT THE FASTER WE WENT. SLOWED TO 220KTS & LEVELED OFF AT 15000'. STATUS MSG, RUDDER PCU. NO QRH TO LOOK AT, RETURNED TO LAND. REPLACED YAW DAMP MODULE & YAW DAMP SERVO.