What was found
ON APPROACH, AFTER GEAR EXTENSION FA NOTICED A BURING PLASTIC SMELL. WHEN RAMPER OPENED MAIN CABIN DOOR, THEY TOLD FA THE AIRCRAFT HAD A BURNING PLASTIC SMELL. REMOVED FROM SERVICE. COMPLIED WITH MCN 62172-01, ISSUE 2, PAR 1A(1-4). DURING INSP NOTICED THAT READING LAMPS AT PSU 1AB WERE CONTACTING THE PLASTIC SURROUND NEAR LAMP SOCKET, CREATING A NOTICABLE BURNING PLASTIC SMELL NEAR THE PSU. REPLACED PSU ASSY AT SEAT 1AB LOCATION REF TASK 25-28-00-000-801 AND 25-28-00-400-801. OPS CHECK GOOD WITH ALL CABIN/COCKPIT LIGHTING ON NO OTHER ODORS NOTICED. RAN ECS SYSTEM WITH APU BLEEDS AND ENGINE BLEEDS. NO ODORS NOTICED. RETURNED TO SERVICE.