What was found
JUST PRIOR TO PUSH BACK, APU AUTO SHUTDOWN AND "BUS LT EMER DC OFF" MESSAGE DISPLAYED ON EAD AND SD. INTERROGATED EPCU CURRENT FAULT AND FAULTS REVIEW NO FAULTS NOTED, CHECKED C/B'S AND RCCB FOUND NO FAULTS T/S IAW FIM 24-30-04-00, STEP 1. R & R R2-5154 (CPN:0006974) IAW SWPM, NO HELP.NEED FURTHER T/S IN PROGRESS. FURTHER T/S IAW 24-30-04-00 STEP 2,3,4,5 AND 6 FOUND R2-17 RELAY WAS BURNED (TERMINAL-B2). R & R LT EMERGENCY CONTROL RLY R2-17 THEN EMERGENCY POWER TEST OK AND EPCU RTS TEST PASSED IAW AMM 24-08-01-5. RETURNED ACFT TO SERVICE.