First, the potentiometer reading
The resistance of the potentiometer can be changed from zero to the nominal resistance. It has three lead-out connectors, and the resistance of the connectors at both ends is the nominal resistance. The intermediate joint can be rotated with the shaft to change the resistance between the ends and the ends. The type, nominal resistance, power, etc. of the potentiometer are printed on the potentiometer housing.
Nominal reading: The first and second digits represent the first and second digits of the resistor, and the third digit represents the multiplier of 10n. E.g:
204 20×104=200KΩ
105 10×105=1000KΩ
Second, electrolytic capacitors:
1, pin identification: long + short –
2. Quality judgment:
1 Electrolytic capacitors are connected by two pins to short-circuit the Electrolytic capacitor;
2 Use a multimeter R × 1K file red, black pen to connect the positive and negative capacitors;
3 Check the size of the capacity. When the multimeter is connected, the capacitor charging hand is swung to the right, the amplitude of the hands is getting larger and larger, and the capacity of the electrolytic capacitor is larger;
4 Check the degree of leakage. As the capacitor discharges, the hands swing back to the left and finally stop at a certain position. If the hands are stopped at the ∞, it means that the leakage of the capacitor is very small and cannot be detected. Generally should be greater than a few KΩ. The leakage resistance is extremely small, indicating that the capacitor quality is better.
5 Capacitor is broken: In the test, if the hands are always in the ∞ position, it indicates that the internal circuit of the capacitor has been opened. If it is at 0, it indicates that the capacitor is broken down and the internal short circuit.
Third, the diode: 1 PN structure into, unidirectional conductivity
1 million meters use R × 1K file (R × 1 file current is too small, R × 10K voltage is too high, easy to damage the diode)
2 good or bad judgment: the two test pens are respectively connected to the two ends of the diode, and a resistance value is measured, and then two strokes are adjusted, and another resistance value is measured. The forward resistance of the diode is very small (about several tens of ohms - several hundred ohms), and the reverse resistance is very large (tens of KΩ - several hundred KΩ). If the positive and negative resistance values ​​differ greatly, the unidirectional conductivity of the tube is good. If both values ​​are small or large, there is a problem with the quality of the tube. (Small, breakdown short circuit, large, open circuit).
3 positive and negative judgment. The resistance is smaller. The pin connected to the black pen is the diode positive pole, and the pin connected to the red pen is the negative pole.
Quadrupole
(1) Judging the base of the triode
Due to the base and emitter, there are two PN junctions between the base and the collector, and the reverse resistance between them is large. The forward resistance is very small, so it is judged by the multimeter ohmmeter (R×100 or R×1K).
1b pole discrimination: first connect any test leads to a certain pin. If the measured resistance is large or small, it is known that it is not the base. Both are very large (or very small), and when the above test is repeated, the resistance is exactly the opposite of the above, and it is very small (or very large). It can be concluded that the identified pin is the base. If the above results are not met, an additional pin should be replaced to re-measure. Until it meets.
2PNP, NPN discrimination: Pay attention to the polarity (pin and test pen) when measuring. When the black test pen is connected to the base and the red test pen is connected to the other two poles, the measured resistance value is small, then the triode can be judged to be NPN type. On the contrary, when the red test pen is connected to the base and the black test pen is connected to the other two poles, the measured resistance value is smaller because the PNP type of the triode can be determined.
3 Judging the collector and emitter: Basic principle: Connect the triode into a basic single-tube amplifying circuit, and measure the collector and emitter by measuring the current amplification factor β of the tube.
4 good or bad: If the two PN junctions of the transistor are both large (open) or very short (short), the transistor is damaged.
NPN type: connect the black test lead to one pin to be tested, the red test lead to the other pin, the base is suspended, and then the pin of the black test lead is pinched with the base (note that it cannot be touched, At this time, the human body resistance is connected between the black test pen and the base. The hand has a deflection angle (α1). Next, replace the black and red test leads and repeat the above process. The deflection angle β is recorded. For the larger deflection angle, the pin connected to the black test pen is the collector, and the pin connected to the red test pen is the emitter.
PNP type: It is the same as the principle of c and e poles of the NPN type triode. The difference is that the pin is pinched twice after the line, and the deflection of the hands is observed through the test pen and the base. The size of the deflection angle of the pointer is the collector of the red pen and the pin of the black pen is the emitter.
Five, thyristor pin, good or bad, trigger ability discrimination
The thyristor has three electrodes, the anode, the cathode, and the gate. The method of measuring the resistance between the poles with a multimeter can judge its quality, triggering ability and pin.
(1) Good or bad judgment:
1R×100 files, measuring the positive and negative resistance between the anode and cathode of the thyristor. The positive and negative resistance values ​​of the normal thyristor should be more than several hundred ohms. If only a few ohms or tens of ohms, the thyristor has been short-circuited.
2 R × 10 or R × 1 position. The forward resistance between the control electrode and the cathode should be small (tens of ohms), and the reverse resistance should be large (tens to hundreds of kiloohms), but sometimes the reverse polarity is not ideal due to the characteristics of the gate PN junction. It is completely blocked, so sometimes the measured reverse resistance is not too large (several KΩ or tens of KΩ). This does not mean that the control characteristics are not good. During the test, if the forward and reverse resistance between the gate and the cathode is small (near zero) or very large, the thyristor is damaged.
(2) Pin discrimination: For the thyristor, only a PN junction is between the control electrode and the cathode, which has a forward conduction and a reverse blocking characteristic. With this feature, the multimeter switch can be placed in the R×1K file, and the forward and reverse resistances of the two pins can be arbitrarily measured. When the resistance between the two pins is small, the pin connected to the black test pen is controlled. In the pole, the red pen is connected to the anode and the remaining one is the anode.
(3) Trigger ability:
1 Set the multimeter's range to R×1, connect the black test lead to the anode, the red test lead to the cathode, and record the position of the lower hand.
2 Then use a wire or a switch to short-circuit the thyristor anode and the control electrode (this is equivalent to adding a control voltage to the control electrode). The thyristor is turned on, and the reading of the hands is several tens of ohms.
3 Then disconnect the wire. If the reading is unchanged, the thyristor is good. This method is only applicable to small-capacity thyristors. For medium-capacity and large-capacity thyristors, it can be tested on the R1/1 file of the multimeter, and then one or two energy-saving 1.5V batteries.
Six, single junction transistor pin discrimination:
1 Emitter e: The multimeter is placed in the R×1K file, and the forward and reverse resistance between the two pins can be arbitrarily measured. The forward and reverse resistances between the two electrodes must be equal (the two pins are respectively A base b1 and a second base b2). Then the remaining pin is the emitter e. (The single-junction transistor is an electrode that draws two ohmic contacts on a high-resistivity N-type silicon semiconductor substrate as two bases b1 and b2, and the resistance between b1 and b2 is the resistance of the silicon wafer itself, positive and negative The same resistance is about 3-10KΩ)
2b1, b2 pole: measure the forward resistance between the emitter and a certain base, the larger the resistance is b1, and the smaller the resistance is b2.
The single-junction transistor not only has a similar shape to a common triode, but also has similarities with the NPN transistor measurement. The emitter e of a single transistor (dual-base diode) exhibits a positive characteristic of the PN junction for both bases b1b2. It is small and large, and has the same characteristics as ordinary NPN transistors. It has the characteristics of no PN junction between b1 and b2 of a single crystal tube, and can be distinguished from ordinary NPN tubes. The forward and reverse resistances between b1 and b2 are all about 3-10KΩ, and the collector and emitter of the NPN transistor are connected in series with a forward PN junction and a reverse PN junction. The positive and negative resistance is measured with a multimeter. The values ​​are large.
Seven, the bridge pile is good or bad and the pin is discriminated
Good or bad: use a PN junction (positive conduction, reverse blocking) between two adjacent steps of the bridge stack. If there are adjacent two pins, the forward and reverse resistances are infinite (open) or very close to 0 ( In case of a short circuit, the bridge pile has been damaged.
Pin: The multimeter R×1K is selected to be connected to the black meter pen with the multimeter, and the red pen is connected to the other three pins. If the three resistance values ​​are small, the selected pin is the negative terminal of the bridge stack output. If there is a large or small, the power supply terminal is input to the bridge stack.
Eight, the stability of the Zener diode and the judgment of the regulation value
1 good or bad, the positive and negative poles are the same as ordinary diodes
2 stable value determination
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