As we all know, a triode is a semiconductor device containing two PN junctions. According to the different connection methods of the two PN junctions, it can be divided into NPN type and PNP type transistors with two different conductivity types.
To test the triode, use the ohm gear of the multimeter and select the R×100 or R×1k gear. Equivalent circuit for the ohm stop of a multimeter. The red pen is connected to the negative pole of the battery in the watch, and the black pen is connected to the positive pole of the battery in the watch.
Suppose we don't know whether the transistor under test is NPN type or PNP type, and we can't tell what electrode each pin is. The first step in testing is to determine which pin is the base. At this time, we take any two electrodes (for example, these two electrodes are 1 and 2), use the two test leads of the multimeter to measure its forward and reverse resistances upside down, and observe the deflection angle of the needles; then, take 1 again , 3 two electrodes and 2, 3 two electrodes, respectively reverse the measurement of their forward and reverse resistance, observe the deflection angle of the needle. In these three upside-down measurements, there must be two measurement results that are similar: that is, in the upside-down measurement, the needle has a large deflection once and a small deflection; the remaining time must be that the deflection angle of the pointer before and after the upside-down measurement is very small. The pin is the base we are looking for.