The criterion for the serviceability of a bipolar transistor is its ability to amplify the signal as many times as it is amplified in the same mode by a guaranteed serviceable device of the same type. You can check whether this is so in various ways.
Instructions
Step 1
Never test transistors directly in the circuit, unless the tester is specifically designed to operate in this mode. But even in this case, the circuit must be de-energized, and all capacitors in its composition must be discharged.
Step 2
If the device is designed to test the transistor outside the circuit, evaporate it.
Step 3
If there is no special device for testing transistors, use a conventional ohmmeter. Make sure that the short-circuit current of its probes does not exceed the maximum allowable for the part. Please note that a dial gauge in ohmmeter mode usually has a positive pole on the black wire, and a digital one - a negative one.
Step 4
If an n-p-n transistor is tested, it should conduct current from base to emitter and from base to collector when the positive pole is applied to the base, and should not conduct when voltage is applied to the junctions in reverse polarity. With a transistor of the pnp structure, the situation is the opposite.
Step 5
If the meter has a bipolar transistor test mode, connect it to the appropriate jack or terminals according to structure and pinout. First switch the device to the mode of measuring the current transfer coefficient of transistors. The instrument will display exactly this parameter. Compare it with your passport.
Step 6
A very interesting technique is checking transistors in operation. Assemble the amplifier stage, blocking generator or multivibrator according to the scheme most suitable for the type of transistor under test. For a multivibrator, you will need a second, guaranteed working transistor (of the same structure, if the multivibrator is symmetrical, or the opposite, if unbalanced). Connect the tested transistor to the circuit, and if it works as it should, it is serviceable. By supplying signals of different frequencies to the amplifier stage or by making the generator work at different frequencies by changing the ratings of its elements, you can find the maximum operating frequency of the transistor. You can measure it with a frequency meter.
