To check bipolar transistors connect one probe of multimeter connect to the base of the transistor, the second probe hold alternately to the emitter and the collector, then adjust the probes sometimes repeat the same steps. Please note that the inside of the electrodes many digital or powerful transistors can be placed in protective diodes between collector and emitter and built-in resistors between base and emitter or in the base circuit if you do not know, by mistake, may find the item is faulty.
When testing field - effect transistors consider the fact that they come in a variety of types. For example, the test transistorswith the shutter on the basis of the isolation layer p-n junction, is. Take an ordinary analog or digital ohmmeter (the second is more convenient).
Measure the resistance between the drain and the source, it must have a small size and be approximately equal in both directions. Now measure forward and reverse resistance of the junction, to do this, connect the test probes to the gate and drain (or source). If the transistor is good, the resistance will be different in both directions.
When I check the resistance between the drain and the source, remove the charge from the gate for this for a couple seconds, close it with the source, if you do not – you will get a unique result. Most low-power field - effect transistors are extremely sensitive to static. Therefore before to take the transistor in hand, make sure that your body is not left charges. To get rid of them, touch the hand of any grounded instrument (battery heating). Powerful field-effect transistors are often equipped with protection against static, but despite this protection when working with them won't hurt.