As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LAX - CREW REPORTED AIRCRAFT BECAME DIFFICULT TO CONTROL. AUTOPILOT AND AUTOTHROTTLES BOTH POPPED OFF. DURING THIS TIME THE MACH TRIM INOP LIGHT WAS FLASHING OFF. EMERGENCY DECLARED FLIGHT RETURNED LAX LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. REPLACED THE DIGITAL FLIGHT GUIDANCE SWITCH CIRCUIT BREAKER AT POSITION C-18 THAT WAS FOUND TRIPPED. SYSTEM GROUND CHECK NORMAL OPERATION.