What was found
(CAN) AFTER DEPARTURE, THE ACFT ENCOUNTERED A DMC 3, FAILURE INFLIGHT. THE FLIGHT CREW ELECTED TO RETURN, THE LANDING WAS NOT OVERWEIGHT & DID NOT REQUIRE ANY DECLARATION OF AN EMERGENCY. THE ACFT WAS MET BY MX & TAKEN OFFLINE FOR TROUBLESHOOTING. DUE FAULT SYMPTOMS OF THIS SNAG, NR 2 TR & NR 2 GCU REPLACED & TESTED SERV IAW AMM 24-32-51 & 24-22-34. CABIN LIGHTS TESTED NORMAL IAW TSM TASK 33-21-00-810-806-A.