What was found
DURING INITIAL TAKEOFF ROLL, FOLLOWING POSITIVE PARKING BRAKE RELEASE CHECK, LT MAIN WHEEL BRAKE LOCKED-UP. TAKEOFF ABORTED DUE TO SLOW ACCELERATION, POOR DIRECTIONAL CONTROL. UNABLE TO MOVE AIRCRAFT UNTIL RT BRAKE APPLIED AND RELEASED, THEN TAXI-IN NORMAL. REPLACED LT MAIN WHEEL BRAKE. ALSO REPLACED PN 4500A2 PARKING BRAKE VALVE ASSY. AS A PRECAUTION IAW OPERATOR REQUEST. REPLACED LT MAIN WHEEL ASSY. DUE TO FLAT-SPOTTED TIRE. AT THIS TIME SUSPECTED FAULT IS IN LT BRAKE ASSY, BRAKE ASSY. QUARANTINED BY OPERATOR FOR FURTHER EVALUATION. (K)