What was found
WHILE PERFORMING 1,200 HOUR CHECK (CODE 340009 ON PAGE 4 OF CHAPTER 5) OF EFIS POWER SUPPLIES, FOUND EFIS TUBES TO BLANK OUT WITH RT GENERATOR OFF AND BUS TIE OPEN. FURTHER INVESTIGATION FOUND 35 AMP CIRCUIT BREAKER B5 (TO FEED PS1B BUS FROM PS1 BUS) ON PANEL ZK TRIPPED. THIS C/B WAS CHANGED. ANOTHER ENGINE RUN TO FUNCTION TEST THIS SYSTEM SHOWED (WITH RT GENERATOR OFF AND BUS TIE OPEN) EFIS TUBES TO REMAIN ON FOR ABOUT 10 SECONDS AND THEN 35 AMP B5 BREAKER WOULD TRIP WITH 22 VOLTS SHOWING ON PS2 BUS (SHOULD READ ZERO). WHILE ISOLATING VOLTAGE SOURCE, FOUND SMOKE COMING FROM SUBPANEL 'C' OF DA PANEL. FOUND LOWER TERMINAL OF 1 AMP BREAKER (PN 7274-2-1) FOR 'EFIS EQUIP NR 1' ABRADED INTO A WIRE BUNDLE.