Testing methods for positive, negative, and mass of crystal diodes

Before use, crystal diodes must undergo positive and negative electrode identification and quality testing. Generally, diodes themselves have positive and negative markings. If you cannot see the logo, you need to use a multimeter (pointer or numeric meter) to detect it. When using a pointer multimeter for detection, turn the multimeter to the 1 k Ω or 100 Ω position to detect the diode. If the measured resistance is only a few hundred ohms (positive resistance value), then the end connected to the black meter rod (i.e. the positive terminal of the power supply in the meter) is the positive terminal, as shown in Figure (a) below; If the measured resistance is several hundred kiloohms (reverse resistance value), then the end connected to the red meter rod (i.e. the negative terminal of the power supply in the meter) is the positive terminal. As shown in Figure (b) below.

The forward resistance value of a diode should generally be below 1 k Ω. The smaller this value, the better the quality (if this value is infinite, it indicates that the diode is internally disconnected). The reverse resistance value should generally be above 100 k Ω. The larger this value, the better the quality (if this value is equal to zero, it indicates that the diode has been broken down). Internal disconnected or broken down diodes cannot be used.

For using a digital multimeter to measure diodes, the multimeter should first be rotated to the position marked with the diode symbol, and the probe should be connected to both ends of the diode. If the meter displays a number between 450 and 600, it means that one end of the red probe is the positive terminal of the diode and the other end is the negative terminal. Swap the direction of the probes and test the multimeter. The displayed number should be greater than 1. If it is not within this range, it indicates that there is a problem with the quality of the diode, as shown in figures (c) and (d) below.