A pointer multimeter determines whether a transistor is good or bad as follows.
① Measure NPN transistor: set the multimeter ohmmeter R × 100 or R × lk, connect the black pen to the base, connect the red pen to the rest of the two poles successively, if the resistance value measured twice is small, then connect the red pen to the base, connect the black pen to the rest of the two poles successively, if the resistance value measured twice is very large, then it means that the transistor is good.
② Measure PNP transistor: the multimeter ohmmeter set R × 100 or R × lk at the red pen connected to the base, the black pen has been connected to the remaining two poles, if the two measured resistance values are small, and then connect the black pen to the base, the red pen has been connected to the remaining two poles, if the two measured resistance values are very large, then the transistor 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 of a transistor pole base, and the black pen connected to the assumption of the base, the red pen has been connected to the remaining two poles, if the two measured resistance values are very small (or about a few hundred ohms to a few thousand ohms), the assumption of the base is correct, and the measured transistor NPN type tube; the same, the same, the measured transistor NPN type tube. If the resistance values are very large (about several thousand ohms to several thousand ohms), then the assumed 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, then you must re-assume 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, C, between the access to the bias resistor, read out the head of the resistance, and then two pens reversed and retested. Then reverse the two pens and retest. 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.
