As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE FIRST CLASS LAV SMOKE DETECTOR WENT OFF, CAUSED BY A BURNED OUT LIGHT BALLAST. THE BALLAST WAS PLACED ON MEL AND THE AIRCRAFT RETURN TO SERVICE. REMOVED AND REPLACED BALLAST, OPERATIONALLY CHECKED LIGHT, CLEARED MEL AND RETURNED TO SERVICE.