What was found
IN CRUISE AT FL 310, TWO CLICKS WERE HEARD FROM BEHIND CAPTAIN'S SEAT (ELECTRICAL). ALL INSTRUMENTS ON FORWARD PANEL FLASHED OFF THEN ON THEN WENT BLACK. SEVERAL ORANGE LIGHTS ON THE OVERHEAD. LASTED ABOUT 30 SECONDS, THEN REPEATED ABOUT 4 MINUTES LATER. APU WAS SWITCHED AFTER FIRST EVENT. AT 1,000 FT SMELLED BURNING WHICH CONTINUED UNTIL TAXI-IN. REMOVED AND REPLACED NR 1 TRANSFER BUS RELAY. SYSTEM OPS CHECKS NORMAL.