How to judge the quality of a transistor base using a multimeter (pointer)
1, Determine which pin is the base, assuming that we do not know whether the tested transistor is NPN or PNP type, and we cannot distinguish what electrodes each pin is. The first step in testing is to determine which pin is the base. At this point, we take any two electrodes (such as 1 and 2), use two multimeter probes to measure their forward and reverse resistance upside down, and observe the deflection angle of the probe; Next, take the 1 and 3 electrodes and the 2 and 3 electrodes, invert and measure their forward and reverse resistances respectively, and observe the deflection angle of the watch needle. In these three inverted measurements, there must be two measurements with similar results: that is, in the inverted measurement, the pointer deviates more once and less once; The remaining measurement must be reversed, and the deviation angle of the pointer before and after measurement is very small. The unmeasured pin this time is the base (b) we are looking for.
2, After identifying the base of the transistor, we can determine the conductivity type of the transistor based on the direction of the PN junction between the base and the other two electrodes. Contact the black probe of the multimeter with the base electrode and the red probe with either of the other two electrodes. If the pointer of the multimeter deviates significantly, it indicates that the tested transistor is an NPN type transistor; If the deviation angle of the pointer on the meter head is very small, then the tested tube is PNP type.
3, Determine collector and emitter:
(1) For NPN type transistors, measure the forward and reverse resistance between the two poles using the black and red probes of a multimeter upside down. Although the deviation angle of the multimeter pointer is small in both measurements, careful observation shows that there will always be a slightly larger deviation angle. At this time, the black probe must be connected to the collector (c), and the red probe must be connected to the emitter (e).
(2) For PNP type transistors, use the black and red probes of a multimeter to measure the forward and reverse resistance between the two poles upside down. If the pointer deviates slightly once, the black probe must be connected to the emitter (e) and the red probe must be connected to the collector (c)
