The failure of our CA6140 lathe to suddenly stop operation during work. Detection: First check the total power supply and insurance and thermal relays, no abnormalities. Let the operator start the lathe again, and the AC contactor KM1 that controls the spindle motor has an action, but cannot be self-locking (see illustration). Continue to press the start button SB1, KM1 high frequency bounce still can not be stable. At the same time, the machine lighting is weak and synchronous strobe, and the rated output of the transformer TC1 is 110V. Check if each switch is