What was found
ON PUSHBACK AND AFTER ENGINE START RIGHT SOURCE OFF LIGHT ILLUMINATED WHEN APPLYING IDG. GROUNDED - YES. GROUND RAN #2 ENGINE. ABLE TO DUPLICATE FAULT MANY TIMES. GCU LOGGED FEEDER FAULT. NOT ABLE TO RESET. REF B737-800 FIM 24-21 TASK 801. ACCOMPLISHED FIM 24-21 TASK 813. REMOVED & REPLACED #2 ENG IDG REF B737-800 AMM 24-11-11, OPS CHECKED #2 ENGINE IDG REF AMM 24-11-00-700-803, RAN BOTH ENGINES TO OPS CHECK BOTH GCU'S NO FAULTS NOTED REF AMM 24-11-00-700-802 STEP 2H(3) & AMM 24-11-00-700-803 STEP 3H(3).