When replacing parts of any equipment, it is often necessary to determine the type of transistor, emitter output, base and collector. On old transistors, the markings are erased, and imported transistors have non-standard markings, which makes it difficult to identify. In this case, the type of transistor is set using an ohmmeter.
For p-n-p transistors, equivalent diodes are connected by cathodes, and “n-p-n” are connected by anodes. Checking with an ohmmeter is reduced to testing the p-n junctions - collector base and emitter-base. The negative output of the ohmmeter at the "p-n-p" is connected to the base, and the positive output alternately to the collector and emitter. For "n-p-n", the connection is made in the reverse order.
Using the device, determine the output of the base by the reverse and forward resistances of the collector and emitter junctions. The base lead is usually in the middle or on the right, so connect the black and red test leads to the right and left lead.
If the indicator shows a high resistance ("1"), then try another combination by connecting to the center and left terminals and to the center and right terminals, alternating the red and black test leads.
If a black probe was connected to the center terminal of the base, then we can assume that the transistor is of the "p-n-p" type. If the red terminal were connected, then the transistor could be attributed to the "n-p-n" type.
Connect the red test lead to the right terminal. The resistance indicator should change its value slightly. Since the junction at the emitter has more resistance than the junction of the collector, the collector pin will be on the left and the emitter on the right. Otherwise, if the value is less, the emitter will be on the left. For reliability, you can measure the transfer coefficient on a special ohmmeter connector.