What was found
DURING AFTER START FLOW #2 ENGINE GENERATOR DOES NOT REMAIN ENGAGED AND SOURCE LIGHT ILLUMINATES. GROUNDED - YES. #2 GCU SHOWS IDG FAULT, RESET FAULT AND STAYED CLEAR. OPERATED #2 ENG IDG AND THE IDG TRIPPED OFF ONCE. AFTER THAT, CYCLED IDG MULTIPLE TIMES ON AND OFF ELECTRICAL BUS WITH FULL ELECTRICAL LOAD WITH NO FAULTS. SUSPECT BTB #2 INTERMITTENT, REPLACED BTB #2 AS PRECAUTIONARY REF B737-800 AMM 24-21-41 AND B737-800 FIM 24-21/821. OPERATED #2 IDG MULTIPLE TIMES AGAIN WITH NO FAULTS. VOLTS AND FREQUENCIES NORMAL.