WHILE FLYING A B737-300; IN CRUISE AT FL330; CAPT DISCOVERED #2 AND #3 TRANSFORMER RECTIFIERS HAD NO OUTPUT AND CIRCUIT BREAKERS WERE TRIPPED. CAUSE UNKNOWN.

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FROM DEN TO IAH; FLT WAS UNEVENTFUL. AT FL330 WITH MOSTLY CLR SKIES; CHKED THRUST REVERSER OP FOR APCH AND LNDG AT IAH. NOTICED HIGHER THAN NORMAL LOAD ON THRUST REVERSER #1. CHKED THRUST REVERSER #2 AND THRUST REVERSER #3 AND THEY WERE INDICATING NO PWR. WE THEN CHKED FOR CIRCUIT BREAKERS POPPED AND FOUND THRUST REVERSER #2 AND THRUST REVERSER #3 TO BE POPPED. CALLED DISPATCH THROUGH COMRDO AND THEY CONNECTED ME TO MAINT. TOLD THEM ABOUT PROB AND ATTEMPTED TO TROUBLESHOOT. MAINT THEN INSTRUCTED ME TO PULL SEVERAL CIRCUIT BREAKERS; ONE AT A TIME; TO TRY TO RESET THE SYS. AFTER A LONG DISCUSSION ABOUT PULLING ANY BREAKERS; I ASKED WHAT EFFECT THIS WOULD HAVE AND IF WE WOULD GO DARK IN THE COCKPIT. HE SAID IT SHOULDN'T. THE FIRST ONE I PULLED PUT US ON STANDBY INSTS AND DARK. PAX CABIN REMAINED PWRED. I IMMEDIATELY RESET THE CIRCUIT BREAKER WHICH RESTORED PWR TO WHERE WE WERE BEFORE. WE RESET ALT WINDOW; RE-ENGAGED AUTOPLT AND VERIFIED NAV. DATA GOOD. I THEN REFUSED TO PULL ANY MORE CIRCUIT BREAKERS. WE WERE CLOSE TO DFW AND IAH; WHICH WERE VFR. WE HAD GOOD PWR ON ACFT. LNDG UNEVENTFUL. CALLED DISPATCH AND MAINT AFTER BLOCK-IN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED NO MASTER OR ANNUNCIATOR WARNING WAS RECEIVED ON THIS ELECTRICAL MALFUNCTION. THE RPTR SAID IT IS BELIEVED THE BREAKERS TRIPPED DURING TAXI FOR TKOF BECAUSE BOTH CREW MEMBERS HEARD WHAT SOUNDED LIKE A SNAP LIKE THE NOISE THE CHART HOLDER RETAINER MAKES. THE RPTR STATED THE CREW FOLLOWED THE MAINT CTLR'S ADVICE ON THE CIRCUIT BREAKER RESET BUT WHEN THE COCKPIT WENT DARK; THAT WAS THE END OF THE TROUBLESHOOTING. THE RPTR SAID MAINT HAS RPTED NO FINDING ON THE CAUSE OF THE TRIPPING OF THE TRANSFORMER CIRCUIT BREAKERS. CALLBACK CONVERSATION WITH RPTR ACN 562256 REVEALED THE FOLLOWING INFO: THE RPTR STATED THE CAPT DISCOVERED THE #2 AND #3 TRANSFORMER RECTIFIERS HAD NO OUTPUT DURING A CHK OF THE TRANSFORMER RECTIFIERS LOAD. THE RPTR SAID THE DISPATCHER AND MAINT CTLR WERE ADVISED OF THIS CONDITION AND REQUESTED WE PULL AND RESET A CIRCUIT BREAKER. THE RPTR STATED THE BREAKER WAS PULLED AND PUT THE COCKPIT IN DARKNESS AND IMMEDIATELY THE BREAKER WAS RESET WHICH RESTORED THE COCKPIT LIGHTING AND OTHER SYS WHICH HA BEEN INTERRUPTED BY THE PWR LOSS. THE RPTR SAID THIS ENDED THE TROUBLESHOOTING AND THE ACFT WAS LANDED NORMALLY WITH #1 TRANSFORMER PWRING THE DC BUS. THE RPTR SAID MAINT HAS NOT RPTED THE MAINT ACTION TO CORRECT THE LOSS OF TRANSFORMER RECTIFIER #2 AND #3.