What was found
EMERGENCY LIGHT AMBER EICAS MESSAGE PRESENT. PERFORMED EMERGENCY LIGHT QUICK BITE TEST & IT FAILED WITH MSG 33-11729-CLASS 29, WELS CONTROL UNIT LAMP DRIVER PWR CIRCUIT FAILED. EMERGENCY LIGHTS AT SEAT ROWS 48 TO 52 ARE INOPERATIVE. SWAPPED WELS CONTROL UNIT 29 & 27. FAULT WENT AWAY & ALL LIGHTS WERE OPS AND QUICK BITE TEST PASSED. RETURNED CONTROL UNITS TO ORIGINAL LOCATIONS & FAULT RETURNED. REPLACED WELS CONTROL UNIT 29. LOADED CORRECT SOFTWARE AND PERFORMED OPS CHECK. OPS CHECK FAILED AND FAULT REMAINED. LET WELS BATTERIES CHARGE, PERFORMED FULL GROUND TEST BITE TEST IAW 33-51-00-07A-343A-A. TEST PASSED. PERFORMED OPS CHECK OF LIGHTS AND ALL PREVIOUSLY AFFECTED LIGHTS ROWS 48-52 ARE NOW OPS & FAULT IS NO LONGER ACTIVE. IAW AMM 33-51-07-01A-720A-A & FIM 33-50-F1-E9A-421A.