What was found
(CAN) CEILING LIGHT, SHORT CIRCUIT. UPON ENTERING AIRCRAFT, THE CABIN ATTENDANT SMELLED SMOKE AROUND ROW 20 AND AFT. PILOT CONFIRMED THE SMELL OF SMOKE AND SAW VISIBLE SMOKE FROM AROUND ROW 20 SEAT AC AND TURNED OFF ALL ELECTRICITY AND THE SMOKE STOPPED. MAINTENANCE WAS CALLED FOR ASSISTANCE. INVESTIGATION/ACTION TROUBLESHOOTING SHOWED AN OVERHEATED LAMP HOLDER PN 404830 AT POSITION 20. THE LAMP HOLDER WAS REPLACED.