What was found
IN CLIMB AT APPROX 7000 FT HEARD LOUD POPPING NOISE THEN APPROX 1 MIN LATER ANOTHER POPPING NOISE FOLLOWED BY POWER LOSS ON NR 3 ENGINE AS INDICATED BY N1 AND N2 AS WELL AS AIRCRAFT YAW. COMPLETED SHUTDOWN OF NR 3 ENGINE. FLIGHT ATTENDANT REPORTED, PASSENGER SAW FIRE FROM ABOVE. ENG 3 FIRE EXTINGUISHER 1 WAS ACTIVATED AS A PRECAUTION. MAINTENANCE REMOVED AND REPLACED OVERSPEED PICKUPS AND ELECTRICAL LEADS DUE TO SHORTING CONDITION, CAUSING OVERSPEED SYSTEM TO SHUT THE ENGINE DOWN. ALL WORK PERFORMED IAW LF-507 MANUAL AND JOBCARD, ALL CHECKS GOOD.