What was found
AFTER APU SHUTDOWN AND EXTERNAL POWER APPLICATION AVIONICS COOLING HORN SOUNDED. GROUNDED - YES. CONFIRMED DEFECT AND ALSO OBSERVED RIGHT "TRANSFER BUS OFF" LIGHT ILLUMINATED. FOUND BUS POWER CONTROL UNIT WITH A "EPDIST/BUS FAULT" LIGHT. PER B737-900 FIM 24-41 TASK 803 CYCLED POWER TO THE BPCU TO REMOVE LOCK OUT CONDITION OF BUS TIE BREAKER. REAPPLIED GRD PWR, RIGHT "TRANSFER BUS OFF" LIGHT EXTINGUISHED, AVIONICS COOLING WARNING HORN OFF. PERFORMED BUS POWER CONTROL UNIT BITE PER FIM 24-41 TASK 801, NO FAULTS.