Polarity identification and quality testing of transistor 1

According to the principle of low forward resistance and high reverse resistance of P-N junction, it can be determined whether it is a PNP transistor or an NPN transistor. Connect the red meter rod (marked as "+" on the multimeter) to one pin, and connect the black meter rod (marked as "1" on the multimeter) to the other two pins to measure two resistance values. Then replace the red meter rod with another pin, and the black meter rod contacts the other two pins to measure two resistance values. If both of these resistance values are very small (usually around 1 kO), then this transistor is PNP type, and the pin contacted by the red meter rod is the base, as shown in Figure 5-76 (a); If the resistance values measured twice are both very large, usually above several hundred kiloohms, it is an NPN transistor, and the pin contacted by the red meter rod is the base, as shown in Figure 5-76 (b).