What was found
DURING COCKPIT PREFLIGHT, CREW HEARD ADF NR 1 CIRCUIT BREAKER TRIP. WITHIN A FEW MOMENTS, THE ODOR OF SOMETHING BURNING WAS DETECTED. REMOVING THE ADF HEAD, THE UNIT SMELLED BURNT. THIS SAME S/N HEAD EXPERIENCED THE SAME THING A YEAR AND A HALF AGO, (545 FLT HRS). PREVIIOUS REPAIR REPORT INDICATED A FAILED POWER SUPPLY BOARD, P/N 701-0314-01.