What was found
DUAL IDG FAILURE ON TAKEOFF ROLL AUTO EVENT UPDATE PERFORMED BPCU BITE PER 24-20 TREE 801. LAST LEG SHOWED LEFT GCU WITH FAULT GCB/WIRING/GCU. RIGHT GCU SHOWED NO FAULTS. RAN ENGINES AT IDLE WITH NO FAULTS. RAN A SECOND TIME AND TAXIED TO RUN UP BLOCKS FOR HI POWER RUNS. NO FAULTS NOTED. TECH SUP RECOMMENDS REPLACING BOTH LEFT AND RIGHT GCU AND PERFORM A IDLE ENGINE RUN. ENGINEERING RECOMMENDS REPLACING L GCB C901 IF NO FAULTS ARE FOUND DURING WIRING CHECKS. REMOVED & REPLACED LH GCU REF.AMM 24-22-02. BPCU TESTS EXT POWER, #1 ENG, #2 ENG, APU SYSTEM OK. REMOVED & REPLACED RH GCU I.A.W. AMM 24-22-02. PERFORMED BPCU TESTS ON EXT POWER, #1 ENG, #2 ENG, AND APU SYSTEMS. TEST PASSED. VERIFIED LEFT & RIGHT IDG DIFFERENTIAL PRESSURE INDICATOR IN NORMAL POSITON.PARTS USED: 1921020,QTY :1 ROTABLE PARTS CHANGE WAS INDICATED - TT # 1921020 SN OFF 2304 IPC REFERENCE # 24-22-02-50 ITEM 30 REMOVED AND REPLACED LEFT GCB C901 PER AMM 24-22-03-401. REQUIRES INSTALLATION TEST PER AMM 24-22-03-424-006 STEP F. (1).