Here's how to judge whether a diode is good or bad:
Use a multimeter to measure the resistance at both ends: connect the red pen and black pen of the multimeter to the two ends of the diode and measure twice. If the measurement value is large or infinite, and the measurement value is smaller after adjusting the meter pen, it means that the diode is good. If the deviation of the resistance value between the two measurements is not large or large, it means that the diode is internally open. If the resistance is small both times, it means that the diode is short-circuited internally.
Measure the diode with the on-off gear of the multimeter: If the multimeter makes a beeping sound, it means that the diode is short-circuited inside.
In addition, you can also use a multimeter to judge the positive and negative poles of the diode:
Measuring ordinary diodes: adjust the multimeter to the diode gear, and when measuring, the voltage is from the positive electrode to the negative electrode, and cannot go from the negative electrode to the positive electrode. When measured with a multimeter, the red watch rod is the positive pole and the black watch rod is the negative pole. The positive electrode touches the positive electrode, and the negative electrode touches the silver negative electrode, and there will be a number 055 pressure drop. When measured in the opposite direction, there is basically no response, indicating that the diode is normal.
Measure a diode with three feet together: when measuring with a multimeter, there is no reaction on this side, and there is a 0 on the opposite sideA voltage drop of 26 indicates that the diode is good.