As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING DESCENT GEN 1 SOURCE OFF LIGHT ILLUMINATED, FOLLOWED QRH. SOURCE OFF LIGHT WOULD NOT STAY EXTINGUISHED. GROUNDED - YES. FOUND IDG FAULT ON GCU. REMOVED AND REPLACED #1 ENG IDG PER B737-800 AMM 24-11-11. FILTERS ON OLD IDG WERE CLEAN. #1 IDG OPS CHECKS GOOD. NO MORE IDG FAULT ON GCU.