As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: ON PUSH BACK AFTER ENG #2 START, SET PARKING BREAK AND LOST ALL PARK BRAKE AND ACCUMULATOR PRESSURE TURNED ON Y PUMP THEN OFF AND LOST BRAKES AFTER ONE APPLICATION. REPLACED PARKING BRAKE CONTROL VALVE 102GG AND ACCOMPLISHED A SATISFACTORY LEAK / OPERATIONAL CHECK PER AMM 32-45-53.