A B737-300 ON DSCNT AT FL290 DECLARED AN EMER DUE TO CRACKLING NOISE AND FLASHING FROM CIRCUIT BREAKER PANEL BEHIND CAPT'S HEAD.

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ON MAR/TUE/04 WHILE CONDUCTING FLT OPS ON FLT TO ZZZ AND ACTING AS FO ON A B737-300; CAPT AND MYSELF; FO; DECLARED AN EMER ENRTE TO ZZZ. WHILE ENRTE APPROX 125 MI OUT OF ZZZ AND BEFORE BEGINNING OUR DSCNT; CAPT NOTICED DURING OUR HRLY CHK THAT OUR OXYGEN PRESSURE GAUGE WAS READING BTWN 300-500 PSI. CAPT NOTED IT; WROTE IT UP IN THE LOGBOOK AND CALLED MAINT TO NOTIFY THEM OF THE EARLY MAINT WRITE-UP. APPROX 10 MINS LATER; I STARTED OUR DSCNT AND WITHIN A FEW MINS I NOTICED A 'CRACKING' NOISE AND 'FLASHING' COMING FROM THE CIRCUIT BREAKER PANEL BEHIND THE CAPT'S HEAD. I NOTIFIED THE CAPT (AS HE COULD NOT SEE IT). CAPT SAID TO DECLARE AN EMER AND 'GET THIS ACFT ON THE GND ASAP.' I DECLARED AN EMER; AND THE CAPT GOT OUT THE FIRE EXTINGUISHER AND FIRED IT AT THE AREA. WE NOTICED THAT THERE WERE APPROX 10-20 CIRCUIT BREAKERS POPPED OUT ON THE LOWER HALF OF HIS PANEL. I CONTINUED THE DSCNT AND SUBSEQUENT LNDG (WITH NO LNDG LIGHTS) WITHOUT FURTHER EVENT. AFTER WE TAXIED IN TO THE GATE; THE FIRST PERSON ON THE ACFT WAS A FIREMAN WITH AN INFRARED HEAT DETECTOR; AND HE WANTED US TO EXIT THE COCKPIT SO HE COULD CHK IT OUT. THE NEXT PERSON WAS A MAINT TECHNICIAN WANTING TO LOOK IT OVER. WE HAD THE PAX EXIT THE ACFT; AND AFTER THEY DID SO I WAS ABLE TO GET MY FLT BAG OUT OF THE COCKPIT AND I WAS ABLE TO GET THE LOGBOOK SO I COULD ENTER THE FLT TIMES. I WAS TOLD TO HANG AROUND A FEW MINS BECAUSE THERE WAS TO BE A CONFERENCE CALL WITH MAINT OFFICE. WE WENT DOWNSTAIRS AND CONDUCTED THE CALL AND WERE TOLD THAT WAS EVERYTHING THEY NEEDED. CAPT AND I WENT BACK UPSTAIRS; GOT OUR BAGS AND LEFT. NEITHER CAPT NOR I ENTERED THE RESULTING EMER WRITE-UP INTO THE LOGBOOK. I BELIEVE IT WAS IN ONE OF THE MAINT PERSON'S POSSESSION AND IT ESCAPED OUR MINDS DUE TO THE EVENT.