Multimeter to detect the working status of transistor

For example, if an amplifier has no output, and one of the base and emitter voltages is 0v (measured on the circuit board), does that mean that the transistor is broken? From the given conditions, it is impossible to determine that the transistor is broken based on the existing data. Two points need to be noted here: the amplifier output ensures that the transistor is used as an amplifier or a switch. In addition, if it is used as an amplifier, then the bias circuit of the tube should be checked first (if there is no bias circuit, the base of the tube should be negative when it works normally).

So can a multimeter be used to determine whether the transistors on a circuit board are good or bad? What will be the voltage at each pole of the transistor when it is working in different stages such as amplification, saturation, and cutoff? Obviously, this method can only be used for reference. It is also necessary to turn off the power to detect the online resistance or even remove the transistor and test it again with a multimeter. As for what the voltage at each pole of the transistor will be like, in the amplification state: uc>;ub>;ue (pnp) or (ue>;ub>;uc (npn), in other words, the emitter junction is forward biased and the collector junction is reverse biased. Saturation state: emitter junction is forward biased; collector junction is forward biased. Cut-off state: emitter junction is reverse biased; collector junction is reverse biased. The specific voltage is determined according to the actual situation, but the above conditions must always be met.

Let's briefly talk about the method of measuring transistors with a multimeter. First, there is no need to disconnect the circuit. You can directly use the voltage range of the multimeter to determine which state the crystal transistor is in.

Measure the collector-emitter voltage, which is approximately between 0.3 and 0.6 V, indicating it is in saturation state.

Measure the collector-emitter voltage. If it is almost equal to the voltage, it is in the cut-off state.

Measure the collector-emitter voltage between 1.0V and (power supply voltage - 1)V in various amplification states.

The voltage between the base and the emitter is 0, but it cannot be confirmed that the transistor is damaged at this time. It needs to be analyzed based on the specific situation.

This article, through the analysis of technical experts, helps novice designers analyze the working status of transistors using a multimeter and answers some of the questions. I hope that after reading this article, everyone will be able to master some skills in using a multimeter to measure transistors, and the design process will become smoother.