What was found
(CAN) AIRCRAFT DEPARTED, 30 KM OUT, REPORTED SMOKE IN THE CABIN. THE SMOKE DISSIPATED AND THE FLIGHT LANDED. MAINTENANCE FOUND THE CABIN TEMP CONTROL HAD A BURND DIODE IN IT. THE CONTROLLER WAS REMOVED AND THE SYSTEM WAS DEFERRED IAW THE MEL. AIRCRAFT THEN CONTINUED OPERATING UNDER THE MEL AND RETURNED TO BASE THAT EVENING. OPEN DIODES IN THE CONNECTOR TO THE LT HEAT EXCHANGER BYPASS VALVE WERE REPLACED AS THE SUSPECT CAUSE OF THE DIODES OVERHEATING IN THE CABIN TEMP CONTROLLER. AIRCRAFT WAS RETURNED TO SERVICE AFTER CLEARING THE DMI.