AN AVRO ARJ 85 WAS RETURNED TO SVC IN NON COMPLIANCE WITH THE ELEVATOR DAMPER CIRCUIT BREAKER PULLED AND COLLARED; BUT WITH NO LOGBOOK DOCUMENTATION.

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PRIOR TO TOWING ACFT OUT OF THE HANGAR; CIRCUIT BREAKERS WERE CHKED TO MAKE SURE THAT THEY WERE ALL SET. FOUND THAT CIRCUIT BREAKER K14 (ELEVATOR DAMPER) WAS PULLED AND COLLARED. I CHKED THE ACFT LOGBOOK AND DEFERRED MAINT LOG. NO ENTRIES WERE LOGGED FOR ABOVE MENTIONED BREAKER. IT WAS DECIDED TO ATTEMPT AN OPS CHK OF THE ELEVATOR DAMPENING SYS. UPON REMOVING COLLAR AND RESETTING BREAKER; THE CIRCUIT BREAKER POPPED IMMEDIATELY. AFTER TROUBLESHOOTING SYS; FOUND THAT A DIODE (CE7) WAS INSTALLED BACKWARDS. THIS ALLOWED A DIRECT SHORT TO GND. I REPLACED THE DIODE AND COMPLETED THE OPS CHK WITH NO DEFECTS NOTED AND THE ACFT WAS RELEASED FOR SVC. THE ELEVATOR DAMPENING SYS WAS JUST INSTALLED PER AN MCD AND THERE IS NO DEFERRAL AT THIS TIME FOR IT. THE MCD WAS COMPLETED IN ZZZ1. ALSO UPON REVIEWING WIRING DIAGRAM (27-34-01 FIGURE 1) THERE IS NO POSSIBLE WAY THIS BREAKER WOULD STAY SET WITH THE DIODE INSTALLED INCORRECTLY. ALSO NOTED WAS THAT AIRSPD LIMITATION FOR PITCH OSCILLATION WAS REMOVED FROM THE COCKPIT.