There occurred many faults in the antenna servo systems since CINRAD/SA put into operation. As the main part of the antenna servo system, the DC azimuth motor is also one of components with frequent faults. A continuous locking fault occurred in DC azimuth motor at Changle radar station in 2014, leading to radar shutdown and tachometer performance degradation, in which the instability of antenna rotational speed resulted in abnormal PUPC in the process of major weather guarantee. The causes of the problem are analyzed by using the test program RDASOT (radar data acquisition system operability), measuring the resistance of the DC azimuth motor, and the feedback voltage of the tachometer according to the controlling process of antenna signals. The results are useful for the maintenance and operation of radar DC motors.