Test method I of the hottest electronic components

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Detection methods of electronic components (I)

the detection of components is a basic function of home appliance maintenance. How to accurately and effectively detect the relevant parameters of components and determine whether the components are normal is not a stereotype. Different methods must be adopted according to different components to judge whether the components are normal. Especially for beginners, it is necessary to master the testing methods and experience of common electronic components. The following introduces the testing experience and methods of common electronic components for reference

I. detection methods and experience of resistors:

1. Detection of fixed resistors. A. connect the two leads (regardless of positive and negative) with the pins at both ends of the resistance respectively to measure the actual resistance value. In order to improve the measurement accuracy, the measuring range should be selected according to the nominal value of the measured resistance. Due to the nonlinear relationship of Ohm scale, its middle division is relatively fine, so the pointer indication value should fall to the middle of the scale as far as possible, that is, within the range of 20% - 80% radians at the beginning of the full scale, so as to make the measurement more accurate. According to the resistance error level. Errors of ± 5%, ± 10% or ± 20% are allowed between the reading and the nominal resistance value respectively. If it is inconsistent and exceeds the error range, it indicates that the resistance value has changed. B. note: when testing, especially when testing dozens of K ω When measuring the resistance of the above resistance values, do not touch the probe and the conductive part of the resistance with your hand; When the detected resistance is soldered from the circuit, at least one head must be soldered to avoid other components in the circuit affecting the test and causing measurement errors; Although the resistance value of the color ring resistance can be determined by the color ring mark, it is best to use a multimeter to test its actual resistance value

2 ﹐ detection of cement resistance. The method and precautions for testing cement resistance are exactly the same as those for testing ordinary fixed resistance

3 detection of fused resistors. In the circuit, when the fusing resistor is fused and open circuit, it can be judged according to experience: if the surface of the fusing resistor is found to be black or charred, it can be concluded that it is caused by the overload of the electro-hydraulic servo valve or proportional valve based on the advantages of the hydraulic loading fatigue testing machine over the traditional experimental method, and the current passing through it exceeds the rated value many times; If there is no trace on its surface and there is an open circuit, it indicates that the current flowing is just equal to or slightly greater than its rated fusing value. For the judgment of the quality of the fused resistor without any trace on the surface, the multimeter R can be used × To ensure the accuracy of measurement, one end of the fuse resistor should be welded off the circuit. If the measured resistance value is infinite, it indicates that the fusing resistor has failed and is open circuit. If the measured resistance value is far from the nominal value, it indicates that the resistance has changed and should not be used again. In the maintenance practice, it was found that a few fused resistors were broken down and short circuited in the circuit, which should also be paid attention to during the detection

4 detection of potentiometer. When checking the potentiometer, first turn the handle to see whether the handle rotates smoothly, whether the switch is flexible, and whether the "click" sound is clear when the switch is on or off. Listen to the sound of friction between the internal contact point of the potentiometer and the resistor. If there is a "rustle" sound, it indicates that the quality is not good. When testing with a multimeter, first select the appropriate resistance gear of the multimeter according to the resistance value of the potentiometer to be measured, and then test according to the following methods

a use the ohm block of the multimeter to measure both ends of "1" and "2", and its reading should be the nominal resistance value of the potentiometer. If the pointer of the multimeter does not move or the resistance value differs a lot, it indicates that the potentiometer has been damaged. B. check whether the movable arm of the potentiometer is in good contact with the resistor. Use the ohm gear of the multimeter to measure both ends of "1", "2" (or "2", "3"), and turn the rotating shaft of the potentiometer counterclockwise to the position close to "off". At this time, the smaller the resistance value, the better. Then slowly rotate the shaft handle clockwise, and the resistance value should gradually increase, the finger in the meter The needle should move smoothly. When the shaft handle is rotated to the extreme position "3", the resistance value should be close to the nominal value of the potentiometer. If the pointer of the multimeter jumps during the rotation of the potentiometer shaft handle, it indicates that the movable contact has a poor contact fault

5. Detection of positive temperature coefficient thermistor (PTC). When testing, use a multimeter R × Gear 1, which can be operated in two steps: A. normal temperature detection (indoor temperature is close to 25 ℃); Contact the two leads with the two pins of PTC thermistor, measure the actual resistance value, and compare it with the nominal resistance value. The difference between the two is ± 2 ω It is normal within. If the difference between the actual resistance value and the nominal resistance value is too large, it indicates that its performance is poor or damaged. B. heating detection; On the basis that the normal temperature test is normal, the second step of test heating test can be carried out. Heat a heat source (such as electric soldering iron) close to the PTC thermistor and monitor whether the resistance value increases with the increase of temperature with a multimeter. If so, it indicates that the thermistor is normal. If the resistance value does not change, it indicates that its performance is degraded and cannot be used anymore. Be careful not to make the heat source close to the PTC thermistor or directly contact the thermistor to prevent it from burning out

6 detection of negative temperature coefficient thermistor (NTC)

(1) measure the nominal resistance value RT

the method of measuring NTC thermistor with multimeter is the same as that of measuring ordinary fixed resistance, that is, selecting a suitable resistance block according to the nominal resistance value of NTC thermistor can directly measure the actual value of RT. However, because NTC thermistor is very sensitive to temperature, the following points should be paid attention to when testing: a ﹐ RT is measured by the manufacturer when the ambient temperature is 25 ℃, so when measuring RT with a multimeter, it should also be carried out when the ambient temperature is close to 25 ℃, so as to ensure the reliability of the test. B. the measured power shall not exceed the specified value to avoid measurement error caused by current thermal effect. C. pay attention to correct operation. During the test, do not hold the thermistor body with your hands to prevent the human body temperature from affecting the test

(2) estimate the temperature coefficient α T

first measure the resistance value RT1 at room temperature T1, then use an electric iron as a heat source, close to the thermistor RT, and measure the resistance value rt2. At the same time, use a thermometer to measure the power consumption of the thermistor aluminum electrolysis process at this time, the direct emission of the aluminum electrolysis process and the alumina production are the main stages of greenhouse gas emission in the aluminum industry chain, and then calculate the average temperature T2 on the surface of the resistance RT

7. Detection of varistor. Use r of multimeter × The forward and reverse insulation resistance between the two pins of the varistor measured at 1K gear is infinite, otherwise, it indicates that the leakage current is large. If the measured resistance is very small, the varistor is damaged and cannot be used

8 ﹐ detection of photosensitive resistance. A. cover the light transmission window of the photoresist with a black piece of paper

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