WDB HAS SMOKE IN COCKPIT AND STRANGE NOISES. EMER DECLARED.

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ON TAXI OUT FROM JFK WE WERE UNABLE TO SHUT DOWN THE APU AND THEN TAXI SINGLE ENG BECAUSE THE APU AND OPERATING GENERATOR KEPT HANDING OFF ITS ELECTRICAL LOAD TO THE OTHER. WHEN THIS CONDITION COULD NOT BE CORRECTED AND WE THEN BEGAN TO FAINTLY SMELL SMOKE; WE RETURNED TO THE GATE. MAINT REPLACED THE APU CTL BOARD AND SAID THE CAUSE OF THE SMELL WAS A HOT APU RELAY. NO FURTHER COMPLICATIONS OCCURRED UNTIL CRUISE IN THE VICINITY OF CMH. THE FLT ATTENDANT IN CHARGE (FAIC) CALLED AND SAID FIRST CLASS PAX WERE BEING ANNOYED BY A STRANGE SOUND IN THE FIRST CLASS SECTION OF THE PLANE. THINKING THE NOISE TO BE A 'BUZZ' IN THE AIR CONDITIONING SYS; I ASKED THE FAIC TO COME TO THE COCKPIT TO HELP US DETERMINE THE SOURCE. SHE WAS TO STAND IN THE COCKPIT DOOR AS I CYCLED BOTH THE L AND R PACKS TO DETERMINE WHICH ONE IT WAS. NEITHER PACK BEING SHUT DOWN AFFECTED THE NOISE. HOWEVER; FROM HER VANTAGE POINT IN THE LIGHTED DOORWAY SHE MADE AN EXCITED AND VERY IMPORTANT OBSERVATION THAT THE FO NOR I COULD SEE BECAUSE OF OUR LOW DENSITY LIGHTING -- THE COCKPIT WAS FILLING UP WITH SMOKE! IMMEDIATELY THEREAFTER THE SMOKE RATHER STRONGLY SMELLED. I TOLD THE FAIC TO PREPARE THE CABIN FOR LNDG AND WE DONNED OUR OXYGEN MASKS. BECAUSE OF MY AGE; I NEED BIFOCALS TO READ; ESPECIALLY IN AREAS OF LOW LIGHT. SINCE THE WDB OXYGEN MASK DOES NOT EASILY ACCOMMODATE THE WEARING OF GLASSES; I DIRECTED THE FO TO READ AND COMPLETE WHILE I FLEW THE PLANE. I DECLARED AN EMER AND REQUESTED A VECTOR TO THE CLOSEST ARPT WHICH WAS CMH. WE LANDED FROM AN ILS APCH TO RWY 10R. I DECIDED AN EVAC TO THE JETWAY INSTEAD OF THROUGH EMER EXITS WOULD BE A BETTER COURSE OF ACTION SINCE THE SMELL AND SMOKE SEEMED TO HAVE SUBSIDED SOMEWHAT. WE FINALLY FOUND THE PROB ABOUT 1:30 MINS AFTER ARR WHEN THE FORWARD EQUIP COOLING FAN CIRCUIT BREAKER POPPED. REMOVAL OF THE SLOW SMOLDERING ELECTRICAL FIRE IN THAT FAN SOLVED ALL OUR PROBS. IN SUMMARY; I FEEL THAT THE SPIRIT OF COOPERATION AND COM BTWN THE CABIN AND FLCS ABOUT A SEEMINGLY NON-THREATENING CONDITION RESULTED IN THE EARLY DISCOVERY OF A VERY REAL AND THREATENING CONDITION. THE FAIC CAME TO THE COCKPIT TO DISCUSS A NOISE BUT DISCOVERED THE SMOKE BEFORE WE DID. THE EARLY DISCOVERY ALLOWED US TO BE VERY MUCH AHEAD OF THE GAME AND GET OUR PLANE TO SAFETY EARLY. IT DID MAKE ME WONDER IF THE FLC COULD BE SLOWLY AND SUBTLY INCAPACITATED BY SMOKE BEFORE SMELLING IT OR SEEING IT; ESPECIALLY AT NIGHT IN LOW LIGHT CONDITIONS. COULD SMOKE DETECTORS BE INSTALLED IN THE CEILING OF THE COCKPITS?