What was found
AT THE BEGINNING OF TAKEOFF ROLL, TRANSFERRED CONTROL TO THE FIRST OFFIECER, AND AIRCRAFT SWERVED LEFT. NEITHER PILOT COULD STOP THE SWERVE, CAPTAIN TOOK CONTROL AND STOPPED THE AIRCRAFT. TAXIED BACK. MAINTENANCE INFORMED THE LEFT BRAKE WAS LOCKED. REMOVED & REPLACED THE BSCU IAW AMM 32-42-72-04. BSCU BITE CHECKED NORMAL WITH ITS ENDING CONFIG CODE DISPLAYED. OKAY TO CONTINUE. AS A PRECAUTION, TAXIED THE ACFT FOR A BRAKE CHECK. DURING EXTENSIVE TAXI, USED NORMAL AND ALTERNATE BRAKES SEVERAL TIMES FROM STOPPED POSITION AND ROLLING. NO PULLING OR GRABBING OF THE BRAKES WAS NOTICED. ACFT OK FOR SERVICE.