What was found
AIRCRAFT WAS GROUNDED. DURING THE TAXI OUT FOR T/O, WHEN THE PARKING BRAKE HANDLE WAS PLACED IN THE PARKED POSITION, THERE WAS NO INDICATION ON THE BRAKE PRESSURE INDICATOR. THIS HAPPENED SEVERAL TIMES. I THOUGHT PERHAPS THE INDICATOR HAD FAILED, SO I PUT THE BRAKE HANDLE IN THE PARKED POSITION AND ADDED ENGINE THRUST AND THE A/C BEGAN MOVING FORWARD. SERVICED YELLOW HYDRAULIC SYSTEM ACCUMULATOR TO PROPER PRESSURE AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK, PER AMM 32-45-00-710-001-A.