What should I do if the photoelectric protection function of the paper cutter fails? Remove the circuit board and carry out a visual inspection. It is found that the substrate around the power bridge pile is discolored, and it is concluded that the bridge pile is burnt out. The bridge pile is powered on and tested, and there is still no response.

        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.