How to test the quality of a triode using a multimeter (pointer)
The on-road test can be divided into power-on state testing or non-power-on state testing. You can measure the base voltage when testing with power on. Generally, silicon tubes are 0.7V. The germanium tube is 0.2-0.3V. Description works fine. Otherwise it is a cut-off state. When the power is off, you can test whether the forward and reverse resistance of the PN junction of the triode is normal. Some transistors cannot be detected normally due to the small resistance or inductance connected in parallel in the circuit, so they can be removed and measured.
The pins of the transistor must be correctly identified, otherwise, not only will the access circuit not work properly, but the transistor may also be burned out. Knowing the type and electrode of the transistor, the method for judging the quality of the transistor with an analog multimeter is as follows:
① Test the NPN transistor: Set the ohm block of the multimeter to "R × 100" or "R × lk", connect the black test lead to the base, and connect the red test lead to the other two poles in succession. If the two measured The resistance values are all small, then connect the red test lead to the base, and connect the black test lead to the other two poles. If the resistance values measured twice are large, it means the transistor is good.
②Measure the PNP transistor: Set the multimeter ohm block to "R × 100" or "R × lk", connect the red test lead to the base, and connect the black test lead to the remaining two poles. If the two measured The resistance values are both small, then connect the black test lead to the base, and connect the red test lead to the remaining two poles. If the resistance values measured twice are large, it means that the transistor is good.
When the marking on the transistor is unclear, you can use a multimeter to initially determine the quality and type of the transistor (NPN type or PNP type), and identify the three electrodes e, b, and c. The test method is as follows:
① Use a pointer multimeter to determine the type of base b and triode: Set the ohm block of the multimeter at "R × 100" or "R × lk", first assume that a certain pole of the triode is "base", and connect the black test lead to the assumed On the base of the base, connect the red test lead to the other two electrodes one after another. If the resistance values measured twice are very small (or about a few hundred ohms to several thousand ohms), then the assumed base is correct. And the transistor under test is an NPN type tube; same as above, if the resistance values measured twice are very large (about a few thousand ohms to tens of kiloohms), then the assumed base is correct and the transistor under test is a PNP type tube. If the resistance values measured twice are larger and smaller, the originally assumed base is wrong. At this time, the other electrode must be re-assumed as the "base" and the above test repeated.
② Determine the collector c and emitter e: Still set the pointer multimeter ohm block at "R × 100" or "R × 1k". Taking the NPN tube as an example, connect the black test lead to the assumed collector c, and the red Connect the test lead to the hypothetical emitter e, and hold the b and c electrodes with your hands (do not make b and c in direct contact), pass the human body, connect a bias resistor between b and C, and read the resistance shown on the meter head. value, then connect the two test leads in reverse and retest. If the resistance value measured for the first time is smaller than the second time, it means that the original hypothesis is established, because the small resistance value of c and e means that the current passing through the multimeter is large and the bias is normal. Today's analog multimeters have an interface for measuring the transistor amplification factor (Hfe). You can estimate the amplification factor of the triode.
