How can I use the multimeter better?
For example, if a power amplifier has no output, and one of the triodes uses a multimeter to measure the voltage between the base and emitter as 0V (measured on the circuit board), does that mean that the triode is damaged? Judging from the given conditions, it is impossible to judge that the triode is broken based on the existing data. There are two points to be noted here: the output of the power amplifier ensures whether the triode is used as an amplifier or a switch tube. In addition, if it is used as an amplifier, then You should first check the bias circuit of the tube (if there is no bias circuit, the base of the tube should be negative when it works normally).
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So can a multimeter be used to judge whether the triode on the circuit board is good or bad? What will the voltage of each pole of the triode work in different stages such as amplification, saturation, and cut-off? Obviously, this method is for reference only. It is also necessary to detect the online resistance after power-off or even remove the triode and use a multimeter to detect it again. As for the voltage of each pole of the triode, in the enlarged 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. Saturated states: emitter junction forward bias; collector junction forward bias. Cut-off state: emitter junction reverse bias; collector junction reverse bias. The specific voltage is determined according to the actual situation, but the above conditions must always be met.
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Let's briefly talk about the method of measuring the triode with a multimeter. First of all, without disconnecting the circuit, you can directly use the voltage file of the multimeter to determine which state the transistor is in.
Measure the voltage between the collector and the emitter, it is about 0.3~0.6v, and it is in a saturated state.
Measure the collector-emitter voltage, which is almost equal to the power supply voltage and is in the cut-off state.
Measure the collector-emitter voltage, between 1.0v~(power supply voltage-1)v, in various amplification states.
The base-emitter voltage is 0, but it is not sure that the triode is damaged at this time, and it needs to be analyzed according to the specific situation.
I hope that after reading this article, you can master some techniques of using a multimeter to measure the triode, and the design process will become smoother.
