What was found
(CAN) A/C ON GROUND AND ALL PAX BOARDED WHEN F/A INFORMED CAPTAIN SMOKE COMING FROM FLOOR VENTS AT ROW 1. AT SAME TIME CREW NOTICED SMOKE ON FLIGHT DECK. STAIRS WERE STILL ATTACHED TO A/C AND DOORS OPEN. CAPTAIN INFORMED F/A TO DEPLANE PAX. GROUND SUPPORT, MAINT CONTROL WAS NOTIFIED. FIRE TRUCKS RESPONDED. MAINT ISOLATED VARIOUS ELECT. SYS EVENTUALLY FINDING CAUSE. NORMAL EQUIP COOLING FAN CCT BREAKER POPPED (FAN OVERHEATING); MEL 21-27-1 ISSD. BATTERY CHARGER CCT BREAKER POPPED - BATTERY CHARGER OVER HEATED; UNIT REPLACED. A/C SYSS GROUND CHECKED SERVICEABLE AND A/C RETURNED TO SERVICE WITH NO FURTHER INCIDENTS.