AN ACR FREIGHTER FLC HAS ELECTRICAL SMOKE IN THE COCKPIT AND THEY DIVERT AND LAND AND EVAC THE ACFT.

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ENRTE FROM ATL TO TPA; APPROX 70 NM N OF TLH AT FL290; SMOKE BEGAN COMING FROM UNDER FO FORWARD PANEL; CREW DONNED OXYGEN MASKS; DECLARED EMER AND STARTED DIVERTING TO TLH. EXECUTED SMOKE SOURCE IDENT CHKLIST TO THE EXTENT THAT TIME PERMITTED; AND ACCOMPLISHED APCH CHKLIST AND BEFORE LNDG CHKLIST PRIOR TO LNDG. AFTER LNDG; PERFORMED LAND EVAC CHKLIST AND EXITED ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID THAT THE CAUSE OF THE SMOKE WAS A FLUORESCENT LIGHT BALLAST THAT WAS LOCATED UNDER THE FLT STATION FLOOR BELOW THE CTR AISLE STAND ON THE FO'S SIDE. IN THIS EVENT A CIRCUIT BREAKER OPENED AND THE ELECTRICAL PWR WAS INTERRUPTED AND THE SMOKE DISSIPATED WHILE THEY WERE ON FINAL APCH TO AN ALTERNATE ARPT. THE RPTR ALLEGED THAT A SIMILAR EVENT HAPPENED SEVERAL WKS LATER TO THE SAME ACFT. HOWEVER; THIS TIME THE CIRCUIT BREAKER DID NOT OPEN AND THE BALLAST CAUGHT FIRE WHILE THE ACFT WAS STILL AIRBORNE. AGAIN THE FLC TURNED OFF OF THE RWY; SHUT DOWN THE ACFT; AND EVACED THE ACFT. ONCE THE ELECTRICAL PWR WAS INTERRUPTED DURING THE SHUTDOWN PROC THE FIRE WENT OUT. THE RPTR ALSO ALLEGED THAT ANOTHER OF HIS COMPANY'S B727- 100'S HAD A SIMILAR FLUORESCENT LIGHT BALLAST OVERHEAT AND THAT CREW DIVERTED INTO THE SAME ALTERNATE ARPT. THE SIMILARITY WAS; OTHER THAN THE SAME FLT NUMBER; THE SAME ARPT USED AS A DIVERSION AND THE SAME BALLAST FAILING -- THAT ALL OF THE FLCS HAD TURNED THE LIGHT OVERRIDE SELECTOR TO 'ALL WHITE' AS THE SUN WAS COMING UP. THIS SELECTION TURNS ALL THE FLUORESCENT LIGHTS AND WHITE CTL STAND LIGHTS COME ON WITH FULL INTENSITY. THIS MAY BE OVERLOADING THESE OLD BALLASTS.