How to test transistor using Multimeter

How to test transistor with Digital Multimeter?

In this post let us discuss about how to test transistor using multimeter. For this purpose keep the multimeter in the Ohmmeter/Continuity mode. Before proceeding further it is good to refresh about basics of BJT.BJT_Schematic_Symbol

  1. If the transistor is an NPN, connect the positive multimeter lead to the Base and the negative to the Collector terminal. The multimeter should indicate continuity, the reading should be about same as reading obtained when the individual diode was tested across its terminals.
  2. With the positive multimeter lead still connected to the Base terminal of the transistor, connect the negative lead to the Emitter terminal. The multimeter should again indicate a forward diode junction.
    Note: If the multimeter does not indicate continuity between the base-collector or the base-emitter, the transistor is open.
  3. Connect the negative multimeter lead to the Base and the positive lead to the Collector. The multimeter should indicate infinity or no connectivity.
  4. With the negative multimeter lead connected to the Base, reconnect the positive lead to the Emitter. There should, again, be no indication  of continuity.
    Note: If a very high resistance is indicated by the multimeter, the transistor is leaky but it may still operate in the circuit. If a very low resistance is seen, the transistor is shorted.
  5. To test a PNP transistor, reverse the polarity of the multimeter leads and repeat the test. When the negative multimeter lead is connected to the Base, a forward diode junction should be indicated when the positive lead is connected to the Collector or Emitter.
  6. If the positive multimeter lead is connected to the Base of a PNP transistor, no continuity should be indicated when the negative lead is connected to the Collector or the Emitter.

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