How to use a digital multimeter to test diodes and transistors

1. Detect diode (diode range) Connect the red pen to the positive pole and the black pen to the negative pole; the forward voltage drop of the diode can be displayed. Normally, it should be displayed as follows: 0.500~0.700 for silicon tubes and 0.150~0.300 for germanium tubes. The voltage drop of Schottky diodes is about 0.2V, ordinary silicon rectifier tubes (1N4000, 1N5400 series, etc.) are about 0.7V, and light-emitting diodes are about 1.8~2.3V. Replace the test pens, and the display shows "1" if it is normal, because the reverse resistance of the diode is very large, otherwise the tube has been broken down. If both the forward and reverse measurements are 0 or 1, it means that the tube is damaged.

2. Detecting transistors (diode gear) Detect transistors according to the above-mentioned method for detecting diodes. First, determine the collector C and emitter E; use a meter to measure the forward voltage drop of the two PN junctions, and both readings are about 0.7V; the collector C has a smaller voltage drop, and the emitter E has a larger voltage drop. The common pole (B pole) is measured twice with a red pen, and this tube is an NPN type; the black pen is used, and this tube is a PNP type. ⊿ The above detection method should be noted during the circuit test: If a resistor of less than 700 ohms is connected at both ends of the PN junction, the displayed value will be smaller. At this time, do not blindly think that the transistor is damaged. You can weld one end of the resistor and then measure it, or you can weld the tube off and measure it. ⊿ The resistance between CE of an ordinary transistor should be infinite. For transistors with internal resistance, there is a certain resistance between CE.