What was found
AFTER PREFLIGHT WHERE ALL SYS TESTED NORMAL, TAXIED OUT OF RAMP. ON FIRST BRAKE CHECK OF CHECKLIST BOTH HAD BREAKS. AFTER ABOUT 200 YRDS TAXING THE "ANTISKID INOP" LIGHT STARTED FLASHING AND THE CIRCUIT BREAKER POPPED. TRYED TO RESET (IAW CHECKLIST) BUT IT POPPED IMMEDIATELY SO STARTED TAXIING BACK TO RAMP. THEN "LO BRAKE PRESS" STARTED FLASHING AND HAD NO BRAKES. WAS TAXIING SLOWLY AND STOPPED THE ACFT WITH THE EMERGENCY BREAK HANDLE. REMOVED AND REPLACE POWER BRAKE MOTOR WITH NEW. ALSO INSTALLED AND OVERHAULED PRESSURE SWITCH. BLED THE BRAKE SYSTEM. WORK IAW MM 32-42-06. OPERATIONAL & LEAK CHECK GOOD.