What was found
TYR - FLT 3773 - DURING WALK-AROUND, FOUND ALL EMERGENCY LIGHTS INOPERATIVE. REMOVED AND REPLACED ALL FOUR POWER SUPPLIES. OPERATION CHECK SATISFACTORY. AIRCRAFT RETURNED TO SERVICE. PART TOTAL CYCLES, 774. REFERENCE OPERATOR CONTROL NR SIMA960141, NR 96ZZZX909, AND NR 96ZZZX910.