What was found
PILOT REPORTED TRANSPONDER INOP, NR1 COMM/NAV INTERMIT. MAINT REPLCD NR1 COMM/NAV AND REMOVED TRANSPONDER FOR REPAIRS. NEXT FLIGHT, PILOT REPORTED NR2 COMM/NAV INTERMIT LOSS OF POWER & THE INTERCOMM INOP. MAINT TROUBLESHOOTING FOUND AUDIO PANEL COMM SELECTOR FUNCTION INOP NR2 COMM/NAV INTERMIT, INTERCOMM INOP & AUTO PILOT AUDIO WARN INOP. CAUSE WAS FOUND TO BE AVIONICS BUS BAR HAD FOUR LOOSE SCREWS WITH SEVERE ARCING. THE LOOSE SCREWS WERE ON THE FOLLOWING C/B, AUTO PILOW, GPS, NAV COMM 1 AND NAV COMM 2. NO MAINT PERFORMED ON ANY ELECTRICAL C/BS SINCE PURCHASE OF AC AND THE BUS IS HIDDEN BEHIND THE MAIN WIRE HARNESS W/LMTD VISUAL OF CB. RECMD AC BE INSP ASAP FOR LOOSE SCREWS ON ALL CIRCUIT BRKRS