What was found
ON TAXI OUT, THE CB POPPED OUT FOR THE POWER BRAKES, AFTER A FEW MINUTES, RESET CB AND RETURNED TO RAMP. AFTER STOPPED ON RAMP, PULLED CB FOR POWER BRAKES. INSPECTED POWER BRAKE AND ANTI-SKID BRAKE SYSTEM, NO DEFECTS NOTED. IAW CUSTOMER REQUEST, REPLACED HYDRAULIC BRAKE PUMP ASSY, PN: 640931, SN: 6768 AND ANTI-SKID POWER PACK MOTOR ASSY, PN: MP50B-1, SN: 2996.