How to repair the rapier falling yarn?

Don't stop when the weft is broken. A) Check whether the weft detector is damaged and the sensitivity is too low. B) Check whether the reset dial number k on the computer board has been dialed. C) The letters 1, 2 and 3 are not lit, so it is necessary to check whether the lead is off-line, 5V output and the sensor is damaged. D) Check whether the positions of the sensor and transmitter disk are correct.