As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER DEPARTURE, THE FLIGHT CREW RECEIVED AN EICAS MESSAGE "AVIONICS SMOKE." THE FLIGHT CREW ELECTED TO RETURN. THE LANDING WAS APPROX 6000 KGS OVER THE MAXIMUM STRUCTURAL LANDING WEIGHT. CFR WAS ON STANDBY AS A PRECAUTION. MX DID PERFORM A BRIEF INSP PRIOR TO THE ACFT EXITING THE RUNWAY. THERE WAS NIL ADVERSE PASSENGER REACTION. SMOKE DETECTION CONTROL UNIT (SDCU) RESET AND CHECKED SERV, PN RAI2800M0706.