The zener diode is generally used to measure the leakage on the oscilloscope. The reverse voltage is gradually applied at both ends of the zener diode, and the leakage current of the zener diode increases gradually when it reaches the critical point. The higher the voltage, the greater the leakage current. Measuring the forward and reverse resistance of the zener diode with a multimeter can only roughly judge its quality.

We all know that the zener diode works in the breakdown state, so we can use this characteristic to distinguish whether it is a common diode or a zener. Use a 500 volt megger, the output end of which is connected with a multimeter in parallel, either a digital meter or a pointer meter. Adjust the voltage range of the multimeter to 500 volts, shake the megger to make the needle deflect in the positive direction, and the red pen is the positive pole.

Then connect the two probes to the two electrodes of the tube to be tested. If the positive and negative electrodes of the tube to be tested are known in advance, connect the red probe to the negative electrode of the tube to be tested. Shake the meter. The voltage measured on the meter is the voltage stabilized value of the voltage stabilizing tube. If the positive and negative electrodes of the tube to be tested are not known, shake it first to check the voltage. If there is no voltage (0.5 V), change the probe and then measure. This method is suitable for detecting voltage stabilizing tubes below 200V. If the measured voltage exceeds 200V, the possibility of diode is high. However, it should be ruled out that this tube is a low back voltage diode.