What was found
REFER PG 4427 (REMOVED AND REPLACED GCU). AFTER DEPART HNL, CLIMB TO FL 270, A FLASH CAME WITH LOUD BANG AND ELECTRICAL BURN SMELL (SMOKE) FROM UNDER S/O PANEL, NR 2 FIELD LIGHT ON, GEN OPEN LIGHT ON, NR 2 TRANSFORMER RECTIFIER READ ZERO VOLTS AND ZERO AMP, TR NR 2 CIRCUIT BREAKER POPPED, AND NR 2 GCU ANNUNCIATOR LIGHT ON, ON S/O PANEL. RETURNED TO HNL. REMOVED AND REPLACED NR 2 TRANSFORMER RECTIFIER, BORROWED FROM CAL AT HNL. TR OPS CHECKS OK IAW MM 24-30-00. RAN NR 2 ENG FOR OPS CHECK OF AC ENG GEN AND NR 2 ELECTRICAL SYS. OPS OK IAW MM 22-20-00.