What was found
#1 SOURCE OFF & GEN BUS OFF LIGHTS ILLUMINATE. STARTED APU AND PUT APU GEN ON LT SIDE #1 GEN VOLTAGE WAS NO VOLTS. GROUNDED - YES. BITE CK OF GCU SHOWED IDG FAULT, CLEARED FAULT, RAN ENGINE, IDG OPERATION RESULTED IN SOURCE LIGHT OFF AGAIN. APPLIED ALT DEACTIVATION PROCEDURES REF MX PROGRAM CHAPT 5 05-07-01 TABLE 3 STEP 9. REMOVED AND REPLACED IDG REF AMM 24-11-11. ALT DEACTIVATION PROCEDURES REVERSED. PERFORMED OPERATIONAL TEST REF AMM 24-11-00 OPS AND LK CK'D GOOD.