What was found
AFTER TAKEOFF AS GEAR WAS RETRACTING CAPTAIN`S 1, 2 & 3 DU'S WENT DARK. MULTIPLE LEVEL 1 & 2 ALERTS, SOME WERE TRANSITORY. THOSE WE WORKED WERE GEN 1 OFF, AC BUS TIE 1, EMER POWER & BATTERY DISCHARGE. CLEANED UP CAC IAW MM 05-50-02. INSPECTED & FOUND NR 1 GCU FAULTED. R & R NR 1 GCU IAW MM 24-21-03-4. PERFORMED OPERATIONS CHECK IAW 24-21-03-5. ALL CHECKED GOOD. GND RAN ALL 3 ENGS IAW JRH CHAPTER 5. SWAPPED POWER FROM ENG TO APU GND. ALL CHECKED GOOD. ACFT OK FOR SERVICE.