You can easily test output transistors with a digital multimeter.
Transistors are electronic devices that amplify and control electric currents. Output transistors can drive large currents, enough to power a speaker up to loud levels of sound. When a music amplifier fails, the cause may simply be a bad output transistor. You can test the transistor with the Hfe or gain function found on today's digital multimeters. It helps to first identify the transistor, determine its gain specification and if it has positive-negative-positive (PNP) or negative-positive-negative (NPN) polarity. When you connect the transistor to the multimeter, the meter will clearly show if the transistor is good or not.
Instructions
1. Examine the transistor closely. You will see a part number printed on its body. Find the part number in the transistor catalog and note its gain and whether its polarity is NPN or PNP. Also note the locations of the transistor's base, collector and emitter pins.
2. Switch the digital multimeter on and turn its function knob to measure transistor Hfe, also called beta or gain. Note that the meter may have separate sockets for NPN and PNP transistor testing, and the base, collector and emitter pins have their own separate places labeled on the socket. Connect the transistor to the appropriate socket, and with the base, collector and emitter pins correctly arranged.
3. Read the Hfe number on the meter's display. It should read roughly between 10 and 200, and it should be close to the gain number in the catalog. If it reads less, the transistor is likely defective or damaged and you should replace it.
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