What was found
DURING TAXI OUT THE "POWER BRAKES" CIRCUIT BREAKER TRIPPED. LOST ALL BRAKING SHORTLY THEREAFTER AND USED THE "EMERGENCY BRAKE" SYS TO STOP THE ACFT. R & R THE POWER BRAKE MOTOR, (PN MP50B-1, SN 3905) PRESSURE SWITCH, (PN GPP1250-73 S/N 0236273) MOTOR TO HYD PUMP COUPLING, (6517108-4 NSN) POWER BRAKE CIRCUIT BREAKER (PN S2899L15.0 ) AND CONTROL RELAY (PN MS24166-D2). OPS & LEAK CHECKS GOOD. REF MM 32-42-04, MM 32-44-20, MM 32-32-42-06, MM 32-44-00 AND MM 32-40-01. SERVICED GEAR AND BRAKE PNEUMATIC BOTTLE IAW MM 12-13-01.