The Darlington transistor is a semiconductor device that is composed of two transistors connecting the emitter of one to the base of the other. The resulting circuit creates a transistor equivalent with larger current-handling capabilities and greater current gain (hFE) across the device. The gain increase is the product of the gain of the two individual semiconductors. If the gain of each is 100, then the overall gain of the Darlington device is 10,000, for example.
Identify the base, collector and emitter leads on the Darlington transistor. The base lead connects to the base of the first transistor in the pair, the collector is connected in common to both components of the pair, and the emitter lead to the emitter of the second transistor. If you are unsure whether the device is an NPN or PNP type, refer to the manufacturer's specification sheet. The steps that follow refer to an NPN-type transistor. Reverse the polarity of the test leads for a PNP-type device.
Turn the multimeter dial to the diode setting. If your tool does not have this option, turn it to the lowest Ohms setting.
Clip or press the positive meter lead to the base lead. If your test leads do not have built-in clips, use the alligator clip jumper to connect the transistor lead and the meter probe. Clipping the probe makes it easier to work with the tiny devices.
Touch the negative test probe to the collector and then the emitter. A properly functioning transistor will show a low hFE (transistor current gain) reading.
Clip the negative meter lead to the base lead of the transistor.
Press the positive lead to the emitter and collector leads. Each reading should display an open circuit (infinite resistance), due to the reverse bias of the test equipment.