As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ACFT WAS TAXIING TO THE RUNWAY, WHEN THE POWER BRAKES AND ANTI SKID SYSTEMS FAILED. THE CREW STOPPED THE ACFT ON THE TAXIWAY. REMOVED FAULTY MOTOR PN MP50B-1, SN 2728. FOUND COUPLER BETWEEN PUMP AND MOTOR WORN EXCESSIVELY. REPLACED COUPLER WITH NEW PN 6517103-4. TROUBLESHOT TO FAULTY POWER BRAKE ELECTRIC MOTOR. INSTALLED O/H UNIT AND OPS CHECK GOOD. PERFORMED ANTI-SKID FUNCTIONAL CHECK GOOD IAW MM 32-44-20.