What was found
FLT 5 - HNL - RADAR/TCAS, F/O SIDE, A SPARK ARCED BETWEEN THE LOWER INST PANEL EYEBALL AIR OUTLET AND RADAR/TCAS DISPLAY UNIT. THE LOUD ARCING SOUNDS WAS 1 TO 2 SEC, AND LOOKED WHITE OR YELLOW. THEN 3 HOURS INTO THE FLIGHT AT 2100 HOURS IT ARCED 2 MORE TIMES IN QUICK SPACES. PULLED C/B D-29 ABOVE F/E. FIRST ARC WAS ABOUT 1/2 HR INTO FLIGHT. REPLACED THE F/O'S RADAR INDICATOR. THE GROUND CHECK WAS OK ON TEST AND THE TCAS SYSTEM TESTED OK. (M)