THE FLC OF AN AT72 STOPPED THE ACFT SHORTLY AFTER TAXI BEGAN IN RESPONSE TO SMOKE IN THE COCKPIT. A MULTI- FUNCTION COMPUTER HAD FAULTED AND THE ELECTRIC SMOKE WARNING LIGHT ILLUMINATED. CHKLIST PROCS FAILED TO ISOLATE THE SMOKE AND THE ACFT WAS SHUT DOWN AND EVACED. ATCT GND CTLR ALERTED CFR. MAINT COULD NOT DUPLICATE AND RPTRS STATE THAT THIS OCCURRED PREVIOUSLY; ALSO REQUIRING ACFT EVAC.

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ON TAXI OUT; ONE OF THE FOUR ON BOARD COMPUTERS FAULTED. I CALLED FOR THE CHKLIST AND STOPPED THE ACFT. WE BEGAN TO SMELL ELECTRICAL SMOKE AND GOT THE 'ELECTRIC SMOKE' WARNING LIGHT. I SHUT DOWN THE L ENG; AND CALLED THE FLT ATTENDANT TO BEGIN AN EVAC OUT THE L SIDE OF THE ACFT. OUR POS WAS ONLY 100 FT FROM WHERE WE HAD BEEN PARKED; IN VIEW OF THE CTL TWR. WE TRIED TO ISOLATE; VIA THE CHKLIST; WHERE THE SMOKE WAS ORIGINATING BUT COULD NOT. SMOKE BEGAN TO FILL THE COCKPIT AND I DECIDED TO SHUT DOWN REMAINING ENG AND ALL PWR TO THE ACFT. AN EMER WAS NOT DECLARED SINCE NO FLAMES WERE VISIBLE AND I KNEW ONCE ALL ELECTRICAL PWR WAS SHUT OFF; WHATEVER WAS SMOKING WOULD STOP; AND IT DID. FIRE TRUCKS WERE DISPATCHED BY THE CTL TWR ONCE THEY SAW PEOPLE EVACING FROM THE ACFT. MAINT PERSONNEL ARRIVED TO FIX THE PLANE; BUT COULD NOT DUPLICATE THE PROB AND SIGNED OFF THE LOGBOOK; THE AIRPLANE THEN FLEW BACK TO DFW WITHOUT FURTHER PROB. THE SAME THING HAPPENED WITH THIS ACFT 6 WKS EARLIER AND AN EVAC FOLLOWED. MAINT PERSONNEL COULD NOT FIND THE PROB THAT TIME EITHER. THE ACFT CONTINUES TO FLY TODAY. SUPPLEMENTAL INFO FROM ACN 328717: #1B MULTI-FUNCTION COMPUTER FAULTED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE MULTI-FUNCTION COMPUTER IS A MGMNT AND MONITORING COMPUTER DESIGNED TO ACT IN LIEU OF SEPARATE ELECTRONIC UNITS FOR EACH OF THE SYS. IT BASICALLY CTLS ELECTRICAL DISTRIBUTION FOR THE ACFT. ITS PRIMARY SOURCE OF PWR IS DC AND THE BACKUP IS OFF THE EMER BUS. THERE ARE 2 MULTI-FUNCTION COMPUTERS AND 2 RELATED MODULES. THE MULTI-FUNCTION COMPUTER HAD SELF TESTED (AMBER FAULT LIGHT FOR 3 SECONDS) DURING INITIAL TAXI. A COUPLE OF MINS LATER; THE MULTI-FUNCTION COMPUTER FAULTED AGAIN. THIS TIME THE FLC RECEIVED AN ELECTRICAL SMOKE WARNING AND SMOKE BEGAN POURING INTO THE COCKPIT BELOW THE CTR CONSOLE. WITH THE INITIAL FAULT; THE FLC WAS ALERTED BY A COMBINATION OF A SINGLE CHIME; A MESSAGE ON THE ALERT PANEL ON THE CTR PEDESTAL; AND A PUSH BUTTON FOR THE MULTI-FUNCTION COMPUTER. THE SUBSEQUENT ELECTRICAL SMOKE WARNING WAS INITIATED BY THE SMOKE DETECTION SYS (FAN AND SENSOR) IN A ZONE UNDER THE COCKPIT FLOORBOARD; BENEATH THE FORWARD CARGO COMPARTMENT. MAINT COULD NOT DUPLICATE THE FAULT -- THERE WERE NO BURNED WIRES; CIRCUITS OR ANYTHING. RPTR WAS LATER TOLD THAT SOME CIRCUITS COULD POSSIBLY BE BURNED OUT IN THE COMPUTER; BUT UNLESS IT FAILED TESTING THEY WOULD NOT REPLACE THE COMPUTER. AS A SIDE NOTE; THE FO STATES THAT WHEN HE TOLD THE FLT ATTENDANTS TO DEPLANE THE PAX; THE FLC WAS NOT AWARE THAT THERE WAS SMOKE IN THE CABIN. THE FLT ATTENDANTS PERFORMED AN EMER EVAC THROUGH THE AFT STAIR AND THE FORWARD L EMER PLUG BECAUSE OF THE PRESENCE OF SMOKE IN THE CABIN.