What was found
NOTE THAT NO REPORT WAS RECEIVED OF VISIBLE SMOKE BEING OBSERVED BY A CREW MEMBER OR PASSENGER. THE AFT LT LAVATORY SMOKE ALARM ACTIVATED DURING APPROACH FOR LANDING AT MSP. THE INTERPHONE COMMUNICATIONS WAS LOST TO THE AFT CABIN. THE PILOT DECLARED AN EMERGENCY AND CFR MET THE ACFT AFTER TOUCHDOWN, VERIFIED THAT NO FIRE, SMOKE, SMELL OR HEAT PER INFRARED SCAN AND ESCORTED THE ACFT TO THE GATE. MX FOUND THE LIGHT BALLAST FOR THE AFT LT LAVATORY WAS CHARRED AND SHOWED EVIDENCE OF INTERNAL DAMAGE. THEY WERE NOT ABLE TO DETERMINE CAUSE FOR LOST OF CABIN INTERPHONE, FAILURE OF AFT SECTION OF CABIN LIGHTING, OR THE INTERMITTENT TAIL CONE LIGHTS. LAV LIGHT BALLAST WAS REPLACED, COALESCER SOCKS REPLACED AND THOSE SYSTEMS FUNCTIONALLY CHECKED.