What was found
DURING CLIMB AT FL250, THE NR 1 ENGINE DRIVEN GENERATOR DISCONNECTED AND A SOURCE LIGHT ILLUMINATED WITH A MASTER COUTION LIGHT ELEC ALSO ILLUMINATED. ATTEMPTED TO RESET THE GENERATOR IT DID NOT RE-POWER THE SOURCE LIGHT. APU WAS STARTED AND IT DID EXTINGUISH THE SOURCE LIGHT. ACFT GROUNDED. TROUBLESHOT DETERMINED IDG FAULT. REMOVED AND REPLACED THE IDG IAW AMM 24-11-11-080-801. NO CONTAMINATION FOUND. INSTALLED AND OPS CHECK NEW IDG IAW AMM 24-11-11-400-801.