AN MD80 WAS DISPATCHED AFTER REPLACEMENT OF THE FLT GUIDANCE PANEL; AT 13000 FT HAD AUTOPLT AND AUTO THROTTLES DISCONNECT AND CIRCUIT BREAKER TRIP. ACFT YAWED R AND THEN L.

Narrative

AFTER ESTABLISHED AT FL370 FOR CRUISE THE AUTO PLT AND AUTO THROTTLES DISCONNECTED AND CB-C18 (DIGITAL FLT GUIDANCE SYSTEM SWITCH) POPPED. THE ACFT YAWED R THEN L. I WAS CONCERNED ABOUT AN UPSET AND STARTED A DSCNT WHILE THE FO GOT A CLRNC FROM ATC. THE DIGITAL FLT GUIDANCE PANEL WAS INOP ON 1 AND 2. THE ALTITUDE ALERT SYSTEM WAS FROZEN. THE SPEED COMMAND BUG WAS FROZEN AND THE PMS WAS INOP. BECAUSE OF THE YAW WE DISCONNECTED THE YAW DAMPER SYSTEM AND DSNDED IN STEPS TO FL240. WE HAND FLEW THE REST OF THE TRIP AND APCH. MAINT IN CONTACT WITH ZZZ1 TECH; CHANGED THE FLT GUIDANCE PANEL AND RESET THE CB AND CLRED US FOR DEP BACK TO ZZZ. PASSING ABOUT 13000 FT THE CB TRIPPED AGAIN WITH THE SAME RESULTS. WE AGAIN ADVISED ATC OF OUR PROB AND CONTINUED TO ZZZ. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE FIRST INCIDENT OCCURRED AT FL370. THE AUTOPLT AND AUTO THROTTLES DISCONNECTED AND A CIRCUIT BREAKER TRIPPED. THE RPTR SAID THE AIRPLANE YAWED TO THE RIGHT; HELD MOMENTARILY THEN CENTERED; THEN YAWED TO THE LEFT HELD MOMENTARILY THEN CENTERED. THE RPTR STATED THE YAW DAMPER WAS SWITCHED OFF AND THE AIRPLANE HAND FLOWN. THE RPTR SAID AFTER MAINT REPLACED THE FLT GUIDANCE PANEL AND TESTED PER THE MAINT MANUAL THE AIRPLANE WAS THEN DISPATCHED. THE RPTR SAID CLBING THROUGH 13000 FT THE DISCREPANCY WAS REPEATED AGAIN AND THE AIRPLANE WAS HAND FLOWN TO THE TRIP TERMINATION. THE RPTR STATED THE AIRPLANE WAS REMOVED FROM SVC AND WAS FOUND TO HAVE A BROKEN WIRE ON THE DUAL ELEVATOR SERVO DRIVE UNIT.