Introduction on How to Use a Multimeter to Test the Quality of a Transistor
First, use the "Diode and Continuity Buzzer" function of a digital multimeter to determine whether a transistor is good or bad and whether it is a PNP or NPN type.
① Set the digital multimeter to the "Diode Test" function. Insert the red test lead into the (VΩ) jack and the black test lead into the (COM) jack. If, when the red test lead is connected to one pin and the resistance values between this pin and the other two pins are around 611Ω or 614Ω, it indicates that the measured transistor is an NPN type. The pin with a resistance value of about 611Ω (a few ohms less) is the collector of the transistor, and the pin with a resistance value of about 614Ω is the emitter. Conversely, if the black test lead of the digital multimeter is connected to one pin and the resistance values between this pin and the other two pins are both around 600Ω, the transistor is a PNP type. Similarly, the pin with the smaller resistance value is the collector, and the one with a slightly larger resistance value is the emitter. If you can't measure a resistance value of around 600Ω between any combination of the three pins using the red and black test leads, the transistor is bad. If the measured resistance value is much less than 600Ω or zero, it also proves that the transistor is bad.
Sometimes, even if you can measure resistance values of around 600Ω for the transistor, you still need to measure the forward and reverse resistance values between the emitter and the collector using the multimeter. For a good transistor, the resistance values from e to c and from c to e should be infinite (∞). Otherwise, it indicates that there is a problem with the transistor.
Note: This does not apply to transistors with damping diodes and those with a damping resistor between the base and the emitter.
② After determining whether the transistor is PNP or NPN, set the digital multimeter to the hFE function. This function has dedicated jacks for measuring low - power transistors. Insert the three pins of the transistor into the corresponding jacks. The digital multimeter will then display the amplification factor of the measured transistor.
