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.
Advice 2 : How to determine the base of the transistor
A bipolar transistor has three electrodes: emitter, collector and base. If the Pinout of the device is unknown, it can be determined empirically. You can use the regular ohmmeter.
Using a sample of the diode, marked the Pinout directly on the body, determine what is the polarity of the voltage on the ohmmeter probes in the measurement mode of resistance. From the gauge it is often the opposite polarity, in which to connect the probes to measure voltage and current. Digital devices of the same polarity in all modes is usually the same. But to implement such a check does not hurt anyway.
Connect the probe of the instrument to one of the terminals of the transistor and then the other probe connect alternately first to one and then to another of the remaining conclusions. If the arrow does not deviate, change the polarity of the test probes and repeat the experience. In the case that to achieve the deflection has failed and in this case, so this conclusion is not basic.
Repeat the above steps for the remaining conclusions of the transistor. Find a combination of electrodes in which a transistor behaves like two diodes connected to either the cathodes or anodes at one point. The conclusion, which summed up the point of their connection, and is the base. But remember that to use the transistor as two diodes because they will interfere with each other.
Define the structure of the transistor. If he behaves like two diodes connected with anodes to the structure - n-p-n, but if it behaves like two diodes connected to the cathodes, then the structure p-n-p.
It remains to determine which of the remaining leads - emitter, and a collector. Assemble a transistor amplifier stage with common emitter. Feed him meals in the correct polarity, depending on the structure (structure n-p-n voltage on the supply bus must be positive, and for the structure p-n-p - negative). If the transistor is properly connected (the emitter on a common cable), its gain will be significantly higher than in case of incorrect connection (when on a common cable header).