1, the detection of fixed capacitors. A detection of small capacitance below 10pF Because the capacity of the fixed capacitor below 10pF is too small, use a multimeter to measure, only qualitatively check whether there is leakage, internal short circuit or breakdown phenomenon. When measuring, use the multimeter R×10k block, and connect the two pins of the capacitor to the two pins of the capacitor. The resistance value should be infinite. If the resistance is measured (the pointer swings to the right) is zero, it indicates that the capacitor is damaged by leakage or internal breakdown. B. Check whether the 10PF to 001μF fixed capacitor is charged, and judge whether it is good or bad. The multimeter uses R×1k block. Both triodes have a beta value of more than 100 and a small penetration current. Can use 3DG6 and other types of silicon triodes to form a composite pipe. The red and black pens of the multimeter are respectively connected to the emitter e and the collector c of the composite tube. Due to the amplification effect of the composite triode, the charging and discharging process of the measured capacitance is amplified, so that the amplitude of the pointer of the multimeter is increased, thereby facilitating observation. It should be noted that: During the test operation, especially when measuring a small-capacity capacitor, it is necessary to repeatedly exchange the measured capacitance pin contact A, B two points in order to clearly see the multimeter pointer swing. C For a fixed capacitance of 001μF or more, use the R×10k block of the multimeter to directly test whether the capacitor is charged and whether there is an internal short circuit or leakage, and estimate the capacity of the capacitor based on the amplitude of the pointer swinging to the right.
2, electrolytic capacitor testing. A Because the capacity of the electrolytic capacitor is much larger than that of the normal fixed capacitor, the appropriate range should be selected for different capacities when measuring. According to experience, under normal circumstances, the capacitance between 1 ~ 47μF can be measured with R × 1k block, and the capacitance greater than 47μF can be measured with R × 100 block. B Connect the red meter of the multimeter to the negative pole and the black lead to the positive pole. At the instant of the moment of contact, the pointer of the multimeter will be deflected to the right by a greater degree of deflection (for the same electrical block, the larger the capacity, the greater the swing amplitude), and then gradually turn to the left Until stopped in a certain position. The resistance at this time is the positive leakage resistance of the electrolytic capacitor, which is slightly larger than the reverse leakage resistance. Practical experience shows that the leakage resistance of electrolytic capacitors should generally be more than several hundred kΩ, otherwise, it will not work properly. In the test, if there is no charging in the forward and reverse directions, ie, the hands are not moving, the capacity disappears or the internal disconnection occurs. If the measured resistance is small or zero, the capacitor has a large leakage current or has been damaged by breakdown. Can not be used again. Cî€ For electrolytic capacitors with unknown positive and negative electrode marks, the above-mentioned method of measuring the leakage resistance can be used to determine. That is, first measure the leakage resistance, remember its size, and then exchange the test leads to measure a resistance. In the two measurements, the one with the largest resistance is the positive connection. That is, the black pen is connected to the positive electrode, and the red pen is connected to the negative electrode. D î€ Use a multimeter to block electricity, and use a method of charging the electrolytic capacitor forward and backward. According to the amplitude of the pointer to the right, the capacity of the electrolytic capacitor can be estimated.
3. Detection of Variable Capacitors A gently rotating the shaft by hand should feel very smooth and should not feel tight or even stuck during loosening. When the axial direction of the loading shaft is pushed forward, rearward, upward, downward, leftward and rightward, the shaft should not be loosened. B. Rotate the shaft with one hand. The other hand gently touches the outer edge of the rotor group and should not feel any looseness. The variable capacitor with poor contact between the shaft and the rotor cannot be used anymore. C. Place the multimeter in an R×10k block. Connect the two test leads to the terminals of the variable capacitor and the stator with one hand. Rotate the other shaft slowly and repeatedly. The pointer of the multimeter should be Infinite position does not move. In the process of rotating the shaft, if the pointer sometimes points to zero, it means that there is a short circuit point between the rotor and the stator; if you touch a certain angle, the meter reading is not infinite but there is a certain resistance, indicating that the variable capacitor is moving There is leakage between the chip and the stator.
2, electrolytic capacitor testing. A Because the capacity of the electrolytic capacitor is much larger than that of the normal fixed capacitor, the appropriate range should be selected for different capacities when measuring. According to experience, under normal circumstances, the capacitance between 1 ~ 47μF can be measured with R × 1k block, and the capacitance greater than 47μF can be measured with R × 100 block. B Connect the red meter of the multimeter to the negative pole and the black lead to the positive pole. At the instant of the moment of contact, the pointer of the multimeter will be deflected to the right by a greater degree of deflection (for the same electrical block, the larger the capacity, the greater the swing amplitude), and then gradually turn to the left Until stopped in a certain position. The resistance at this time is the positive leakage resistance of the electrolytic capacitor, which is slightly larger than the reverse leakage resistance. Practical experience shows that the leakage resistance of electrolytic capacitors should generally be more than several hundred kΩ, otherwise, it will not work properly. In the test, if there is no charging in the forward and reverse directions, ie, the hands are not moving, the capacity disappears or the internal disconnection occurs. If the measured resistance is small or zero, the capacitor has a large leakage current or has been damaged by breakdown. Can not be used again. Cî€ For electrolytic capacitors with unknown positive and negative electrode marks, the above-mentioned method of measuring the leakage resistance can be used to determine. That is, first measure the leakage resistance, remember its size, and then exchange the test leads to measure a resistance. In the two measurements, the one with the largest resistance is the positive connection. That is, the black pen is connected to the positive electrode, and the red pen is connected to the negative electrode. D î€ Use a multimeter to block electricity, and use a method of charging the electrolytic capacitor forward and backward. According to the amplitude of the pointer to the right, the capacity of the electrolytic capacitor can be estimated.
3. Detection of Variable Capacitors A gently rotating the shaft by hand should feel very smooth and should not feel tight or even stuck during loosening. When the axial direction of the loading shaft is pushed forward, rearward, upward, downward, leftward and rightward, the shaft should not be loosened. B. Rotate the shaft with one hand. The other hand gently touches the outer edge of the rotor group and should not feel any looseness. The variable capacitor with poor contact between the shaft and the rotor cannot be used anymore. C. Place the multimeter in an R×10k block. Connect the two test leads to the terminals of the variable capacitor and the stator with one hand. Rotate the other shaft slowly and repeatedly. The pointer of the multimeter should be Infinite position does not move. In the process of rotating the shaft, if the pointer sometimes points to zero, it means that there is a short circuit point between the rotor and the stator; if you touch a certain angle, the meter reading is not infinite but there is a certain resistance, indicating that the variable capacitor is moving There is leakage between the chip and the stator.
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