Discrimination and detection of transistor electrode damage
To distinguish the three electrodes of a transistor with unclear or unmarked model markings, a multimeter can also be used for testing.
First, set the range switch of the multimeter to the R×100 or R×1k resistor position. The red probe contacts one electrode of the transistor at will, and the black probe contacts the other two electrodes in sequence to measure the resistance between them. If the measured resistance is several hundred ohms, then the electrode contacted by the red probe is the base b, and this transistor is a PNP transistor. If high resistance ranging from tens to hundreds of kilo ohms is measured, the electrode in contact with the red probe is also the base b, which is an NPN transistor.
On the basis of distinguishing the transistor type and base b, the collector is determined using the principle that the forward current amplification factor of the transistor is greater than the reverse current amplification factor. Assuming that one electrode is the c electrode and the other electrode is the e electrode.
Set the range switch of the multimeter to the R×1k resistor position. For PNP tubes, connect the red probe to the c pole and the black probe to the e pole. Then, pinch the b and c poles of the tube with your hand, but do not directly touch them to measure a certain resistance value. Then swap the two probes for a second measurement and compare the resistance between the two measurements. For PNP type tubes, the electrode connected to the red probe is the collector electrode for the smaller resistance. For a low resistance NPN transistor, the electrode connected to the black probe is the collector electrode.
