What was found
AFTER STARTING THE ENGS WE GOT AN APU FAULT CAS MSG. SHUTDOWN THE APU THEN THE ESS BUS TURNED AMBER ON THE ELEC SYNOPTIC. SHUTDOWN ENGS & POWERED DOWN ACFT. FOUND ESS BUS 7 1/2 CB POPPED ON THE J BOX ABOVE THE NR 1 BATTERY. ALSO NOTED ELEC SMELL IN FWD SERVICE COMPARTMENT. REMOVED LT ELEC J BOX COVER & NOTED A STRONG BURNT ELEC SMELL. APPLIED POWER TO ACFT & FOUND THAT ESS B 512KA CB WILL NOT RESET. TROUBLE SHOT TO A BURNT CONTACTOR 7KA. R & R 7KA CONTACTOR WITH NEW & APPLIED POWER, CB STAYED RESET, BUT APU STARTS AUTOMATICALLY. REMOVED PCB 544PC1 & INSTALLED AN INSPECTED ASSEMBLY, OPS CHECKS WERE GOOD IAW MM 24-61-05-900-801. CARD PN 220CE04Y02, SN 231. CONTACTOR PN 215CC02Y1, SN 882.