After removing the circuit board and conducting visual inspection, it was found that the substrate around the power bridge pile was discolored, it was concluded that the bridge pile was burnt out, and the bridge pile was powered on and the test was carried out. Measured with a multimeter, the newly replaced bridge pile has also been burned out, thus judging that there is a short circuit part. Checking the components one by one from the bridge stack, it was found that a three-terminal voltage stabilizer block (7805) was broken down, the component was purchased to replace, and the power indicator on the circuit board turned on after powering up.

        The operator installs the circuit board on the machine, and operates according to the normal procedure to check whether the photoelectric protection function is working, covering the optical eye with his hand, and the falling knife stops immediately. After several attempts, it is normal. The fault is eliminated.