With a multimeter (pointer) how to measure the good and bad transistors
In-circuit test can be divided into power-on state test or no power-on state test. In the power state test can measure the base voltage. Generally speaking, the base voltage of silicon tube is 0.7V, and that of germanium tube is 0.2-0.3V, which indicates that it is working normally. Otherwise, the cut-off state. No power state can measure the triode PN junction of the forward and reverse resistance is normal. Some transistors can not be detected properly due to the parallel connection of small resistors or inductors in the road, which can be removed and measured.
Triode pin must be correctly identified, otherwise, access to the circuit not only can not work properly, but also may burn the transistor. You know the type of transistor and electrode, pointer multimeter to identify the transistor is good or bad as follows: ① Measurement of NPN transistor.
① measure NPN transistor: the multimeter ohm block set "R × 100" or "R × lk" at the black pen connected to the base, the red pen has been connected to the rest of the two poles, if the two measured resistance values are small, and then the red pen connected to the base, the black pen has been connected to the rest of the two poles, if the two measured resistance values are very large, it is shown that the transistor is good.
② Measurement of PNP transistor: the multimeter ohm block set "R × 100" or "R × lk" at the red pen on the base, the black pen is connected to the base of the transistor.
Pole, the black pen successively connected to the remaining two poles, if the two measured resistance values are small, and then the black pen connected to the base, the red pen successively connected to the remaining two poles, if the two measured resistance values are very large, it shows that the triode is good.
When the marking on the transistor is not clear, you can use a multimeter to determine the initial good or bad transistor and type (NPN type or PNP type), and identify the e, b, c three electrodes. Test methods are as follows
① pointer multimeter to determine the base b and the type of transistor: the multimeter ohm block set "R × 100" or "R × lk" at the first assumption that the triode of a pole "base", and the black pen on the assumption of the base, the red pen successively connected to the remaining two poles, if the resistance value of the two measurements are very small (or about a few hundred ohms to a few thousand ohms), the assumption that the base pole is correct, and the measurement of the triode for NPN type tubes. Triode for NPN type tube; ditto, if the two measured resistance values are very large (about thousands of ohms to tens of thousands of ohms), then the assumption of the base is correct, and the triode under test is a PNP type tube. If the two measured resistance value is a large and small, then the original assumption of the base is wrong, it must be re-assumed that the other electrode for the "base", and then repeat the above test.
② judge the collector c and emitter e: still pointer multimeter ohm block set "R × 100" or "R × 1k" at the NPN tube, for example, the black pen connected to the assumption of the collector c, the red pen connected to the assumption of the emitter e, and hand pinch the b and c poles ( can not make direct contact with the b, c ), through the human body, quite b, between C access to the bias resistor, read out the head of the resistance shown, and then the two pens are reversed and reconnected to repeat the above test. Then the two pens are reversed and retested. If the first measured resistance is smaller than the second, that the original hypothesis is valid, because c, e asked the resistance value is small that the current through the multimeter is large, the bias is normal. Now the pointer multimeter have to measure the triode amplification (Hfe) interface. You can estimate the amplification of the triode.
