What was found
RDU - FLT 2990 - EN ROUTE FROM LGA TO PBI, THE NR 1 BUS OFF LIGHT ILLUMINATED. CREW STARTED APU BUT WAS UNABLE TO POWER THE BUS. FLIGHT DIVERTED TO RDU AND LANDED WITHOUT FURTHER INCIDENT. NO EMERGENCY WAS DECLARED. MAINTENANE FOUND A TENNIS RACKET BEHIND CO-PILOTS SEAT NOT IN A PROTECTIVE COVER. REMOVED SAME. FOUND TRANSFER BUS CIRCUIT BREAKER POPPED. RESET TRANSFER BUS CIRCUIT BREAKER AND RAN ENGINES. ITEM REPEATED SEVERAL TIMES. MAINTENANCE REPLACED APU GENERATOR CONTROL UNIT, NR 1 NORMAL BUSS TRANSFER RELAY. NO FURTHER ITEMS. OPERATIONAL CHECK NORMAL PER MM. (M)