What was found
MID-FLIGHT, EMERGENCY POWER ON ALERT ILLUMINATED. REVIEWED CHECK 20-30 WEST OF LIT, BATTERY LOW ALERT ILLUMINATED. SHORTLY THEREAFTER MULTIPLE ELECT ALERTS OCCURRED. INCLUDING FCC 1B FAULT, FADEC ALT, ALL 3 ENGINES AND OTHERS. CAPTAIN, NR 1 AND NR 3 DU FAILED. NR 2 DU GAVE ATTITUDE ONLY, NO SPEED OR ALTITUDE. EMERGENCY DECLARED. CHECKLISTS COMPLETED. ON FINAL, LEFT EMERGENCY AC BUS FAIL OCCURRED. INSTALLED NEW AC BUS 1 SENSING RELAY IAW SMP A-3-15. ALL OPERATIONS /FUNCTIONS APPEAR TO BE NORMAL, AIRCRAFT ENGINE RUN COMPLETE OPS CHECK, GOOD.