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This might seem a basic questions but I am relatively new to circuit implementations and working with PCBs. I suspect that one of my transistors is burned. I am using 2N3904.

For example, is checking short circuit between base to emitter a good idea (should there be a short circuit between these two legs)? I know the theoretic properties of a transistor, but giving it some current I, in the base and checking if the emitter current is (\beta times I), does not feel to me like a very good idea.

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  • \$\begingroup\$ This is not possible in circuit (as you seem to be asking) unless you have a thorough enough understanding of the circuit to recognize specific issues. Generally speaking usage of the term "burned" suggests that is not the case. If you want practical help, you'll need to edit a schematic diagram of the circuit into the question, and annotate it with things like voltage readings which are leading you to suspect that there is a problem. \$\endgroup\$ – Chris Stratton Jun 3 '19 at 18:21
  • \$\begingroup\$ testing at a low voltage (like diode test mode on a multimeter) with the curcuit powered off (and all capacitors discharged etc) will not damage ordinary parts. - it may not be possible to get good answers with the part in-circuit but it is most unlikely to do further damage, \$\endgroup\$ – Jasen Jun 3 '19 at 18:57
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You'll need to take the transistor off the board and follow these steps (for an NPN transistor):

Step 1: (Base to Emitter)

Hook the positive lead from the multimeter to the to the BASE (B) of the transistor. Hook the negative meter lead to the EMITTER (E) of the transistor. For an good NPN transistor, the meter should show a voltage drop between 0.45V and 0.9V. If you are testing PNP transistor, you should see “OL” (Over Limit).

Step 2: (Base to Collector)

Keep the postitive lead on the BASE (B) and place the negative lead to the COLLECTOR (C).

For an good NPN transistor, the meter should show a voltage drop between 0.45V and 0.9V. If you are testing PNP transistor, you should see "OL" (Over Limit).

Step 3: (Emitter to Base)

Hook the positive lead from the multimeter to the to the EMITTER (E) of the transistor. Hook the negative meter lead to the BASE (B) of the transistor.

For an good NPN transistor, you should see “OL” (Over Limit).If you are testing PNP transistor, the meter should show a voltage drop between 0.45V and 0.9V.

Step 4: (Collector to Base)

Hook the positive lead from the multimeter to the to the COLLECTOR (C) of the transistor. Hook the negative meter lead to the BASE (B) of the transistor.

For an good NPN transistor, you should see “OL” (Over Limit).If you are testing PNP transistor, the meter should show a voltage drop between 0.45V and 0.9V.

Step 5: (Collector to Emitter)

Hook the postitive meter lead to the COLLECTOR (C) and the negative meter lead to the EMITTER (E) – A good NPN or PNP transistor will read "OL"/Over Limit on the meter. Swap the leads (Positive to Emitter and Negative to Collector) – Once again, a good NPN or PNP transistor should read “OL”.

Source: https://vetco.net/blog/test-a-transistor-with-a-multimeter/2017-05-04-12-25-37-07

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  • \$\begingroup\$ So cool.. Thanks!! \$\endgroup\$ – user135172 Jun 4 '19 at 6:17

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