The detection of components is a basic skill of home appliance maintenance. How to accurately and effectively detect the related parameters of components and judge whether the components are normal or

The detection of components is a basic skill of home appliance maintenance. How to accurately and effectively detect the related parameters of components and judge whether the components are normal or not? The detection of components is a basic skill of home appliance maintenance. How to accurately and effectively detect the relevant parameters of components and judge whether the components are normal or not is not a stereotyped thing. Different methods must be taken according to different parts to judge whether the parts are normal or not. Especially for beginners, they need to master the testing methods and experience of common components. The following introduces the testing experience and methods of common electronic components for reference. First, the detection method and experience of resistance: 1. Detection of fixed resistance. Answer: By connecting two probes (positive or negative) to the pins at both ends of the resistor, the actual resistance value can be measured. In order to improve the measurement accuracy, the measurement range should be selected according to the nominal value of the measured resistance. Because of the nonlinear relationship of the ohmmeter scale, the middle section of the scale is subdivided, so the indicated value of the pointer should fall in the middle section of the scale as far as possible, that is, within the range of 20% ~ 80% radians from the starting point of the full scale, so as to make the measurement more accurate. According to different resistance error levels. The error between the reading and the nominal resistance is 5%, 10% or 20% respectively. If not, it is beyond the error range, indicating that the resistance value has changed. B. Note: When testing, especially when measuring the resistance of tens of kω or more, do not touch the conductive parts of the contact pins and resistors; When the measured resistance is welded from the circuit, at least one head should be welded to avoid other components in the circuit from affecting the test and causing measurement errors; Although the resistance value of the color ring resistor can be determined by the color ring symbol, it is best to use a multimeter to test its actual resistance value. 2。 Detection of cement resistance. The methods and precautions for detecting cement resistance are exactly the same as those for detecting ordinary fixed resistance. 3。 Detection of fuse resistance. In the circuit, when the fuse resistor is blown, it can be judged according to experience: if the surface of the fuse resistor is found to be black or burnt, it can be concluded that the load is too heavy and the current flowing through it exceeds the rated value many times; If its surface is open and there is no trace, it means that the current flowing is just equal to or slightly greater than its rated fuse value. To judge the quality of the fused resistor without any trace on the surface, the multimeter R× 1 can be used to measure it. In order to ensure the accuracy of measurement, one end of the fuse resistor should be welded to the circuit. If the measured resistance is infinite, it means that the fuse resistance has failed and opened. If the measured resistance is far from the nominal value, it means that the resistance is variable and should not be used again. In the maintenance practice, it is found that a few fuse resistors are short-circuited, so we should also pay attention to it when testing. 4。 Potentiometer detection. When checking the potentiometer, first turn the knob to see whether the knob rotates smoothly, whether the switch is flexible, whether the switch clicks when it is turned on or off, and listen to the sound of the internal contact of the potentiometer rubbing against the resistor. If there is a rustling sound, it means the quality is not good. When testing with a multimeter, first select the appropriate resistance off position of the multimeter according to the resistance value of the potentiometer to be tested, and then test in the following way. Answer: Measure both ends of "1" and "2" with an ohmmeter, and the reading should be the nominal resistance of the potentiometer. If the multimeter pointer does not move or the resistance value varies greatly, it means that the potentiometer is damaged. B. Check whether the contact between the movable arm of the potentiometer and the resistor is good. Measure both ends of "1" and "2" (or "2" and "3") with an ohmmeter, and turn the potentiometer shaft counterclockwise to the position close to "off". The smaller the resistance, the better. Then slowly turn the handle clockwise, the resistance value should gradually increase, and the pointer in the table should move smoothly. When the important official handle is turned to the limit position "3", the resistance should be close to the nominal value of the potentiometer. If the multimeter pointer jumps during the rotation of the potentiometer shaft handle, it means that the moving contact has a fault of poor contact. 5。 Detection of positive temperature coefficient thermistor (PTC). When testing, use multimeter R× 1, which is divided into two steps: a. Normal temperature testing (indoor temperature is close to 25℃); The actual resistances of the two probes touching the two pins of PTC thermistor are measured and compared with the nominal resistances. It is normal if the difference between them is within 2ω. If the actual resistance is too different from the nominal resistance, it means that its performance is poor or damaged. B. heat detection; On the basis of normal room temperature test, the second step test can be carried out? Heating detection: heat a heat source (such as an electric soldering iron) near the PTC thermistor, and monitor whether its resistance value increases with the increase of temperature with a multimeter. If yes, the thermistor is normal; If the resistance value remains the same, it means that its performance has deteriorated and it can no longer be used. Be careful not to let the heat source be too close to PTC thermistor or directly contact thermistor to prevent burns. 6。 Negative temperature coefficient (NTC) detection. (1), measuring 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, according to the nominal resistance value of NTC thermistor, the actual value of Rt can be directly measured by selecting the appropriate electric barrier. 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 multimeter, it should also be carried out when the ambient temperature is close to 25℃ to ensure the reliability of the test. b？ The measured power shall not exceed the specified value, so as to avoid the measurement error caused by the thermal effect of current. Pay attention to correct operation. When testing, do not pinch the thermistor by hand, so as to avoid the influence of human body temperature on the test. (2) Estimation of temperature coefficient αt First, measure the resistance value Rt 1 at room temperature T1,then use an electric soldering iron as a heat source, close to the thermistor Rt, measure the resistance value Rt2, and measure the average temperature t2 on the surface of the thermistor Rt with a thermometer, and then calculate. 7 detection of varistor. Use multimeter R× 1k to measure the positive and negative insulation resistance between the two pins of the varistor, which is infinite, otherwise the leakage current is large. If the measured resistance is small, the varistor is damaged and cannot be used. 8。 Detection of photosensitive resistance. A: Cover the light-transmitting window of the photoresistor with a piece of black paper. At this time, the multimeter pointer basically remains motionless, and the resistance is close to infinity. The larger the value, the better the performance of the photoresistor. If this value is small or close to zero, it means that the photoresistor has been burnt out and cannot be used any more. B aim the light source at the light-transmitting window of the photoresistor. At this time, the multimeter pointer should swing greatly, and the resistance value is obviously reduced. The smaller the value, the better the performance of the photoresistor. If this value is large, even infinite, it means that the internal open circuit of the photoresistor is damaged and cannot be used any more. C. Place the light-transmitting window of the photoresistor on the incident light, and shake it on the upper part of the light-shielding window of the photoresistor with small black paper to make it receive light intermittently. At this time, the multimeter pointer should swing left and right with the shaking of black paper. If the multimeter pointer stops at a certain position and does not swing with the shaking of the paper, it means that the photosensitive material of the photosensitive resistor has been damaged. Second, the detection method and experience of capacitor 1. Detection of fixed capacitors A. Detection of small capacitors below 10pF Because the capacity of fixed capacitors below10pf is too small, we can only use a multimeter to qualitatively check whether there is leakage, internal short circuit or breakdown. When measuring, you can choose to use a multimeter R× 10k, and use two probes to connect the two pins of the capacitor at will, and the resistance value should be infinite. If the measured resistance (the pointer swings to the right) is zero, it indicates that the capacitor is damaged due to leakage or internal breakdown. B. Detection 10pf ~ 0? Whether the 0 1μF fixed capacitor is charged or not, and then judge its quality. Select R× 1k range for multimeter. The β values of both transistors are above 100, and the penetration current is higher. Silicon triodes of 3DG6 and other models can be selected to form composite pipes. The red and black probes of the multimeter are respectively connected with the emitter E and the collector C of the composite pipe. Due to the amplification of the compound triode, the charging and discharging process of the measured capacitor is amplified, which makes the pointer swing of the multimeter larger and easier to observe. It should be noted that in the test operation, especially when measuring a small capacity capacitor, it is necessary to exchange the A and B contacts of the capacitor pin to be measured repeatedly, so as to obviously see the swing of the multimeter pointer. Detection of triode; Nowadays, most common triodes are plastic-sealed. How to accurately judge which of the three pins of a triode are B, C and E? The B pole of triode is easy to measure, but how to determine which is C and which is E? Three methods are recommended here: the first method: for the pointer instrument with transistor hFE socket, first measure the B pole, then insert the transistor into the socket at will (of course, the B pole can also be inserted accurately), measure the hFE value, and then measure the lamp tube again in reverse. When the hFE value is relatively large, the insertion position of each pin is correct. The second method: For the meter without hFE measuring jack, or the meter with too large tube to be inserted into the jack, you can use this method: For the NPN tube, measure the B pole first (whether the tube is NPN or PNP, its B pin is easy to measure, right? ), put the watch into the r×1kΩ file, connect the red stylus to the imaginary E pole (be careful not to touch the pen tip or pin of the watch), and connect the black stylus to the imaginary C pole. At the same time, hold the pen tip and pin with your fingers, pick up the tube, lick the B pole with your tongue, and see that the pointer on the instrument should have a certain deflection. If the pen is connected correctly, the pointer deflection will be greater. Therefore, the C and E poles of the pipeline can be determined. For PNP tube, connect the black stylus to the hypothetical E pole (do not touch the pen tip or pin) and connect the red stylus to the hypothetical C pole. Hold the nib and this pin with your fingers at the same time, and then lick the B pole with the tip of your tongue. If the pen is connected correctly, the pointer on the meter head will deviate greatly. Of course, when measuring, the pen and the pen should be exchanged twice, and the final judgment can only be made after comparing the readings. This method is suitable for all shapes of transistors, which is convenient and practical. According to the deflection amplitude of the watch hand, the amplification ability of the electron tube can also be estimated, which is of course based on experience. The third method: first determine the NPN or PNP type of the pipeline and its B pole, and then put the electric meter into the r×10kΩ file. For NPN tube, when the black contact pin is connected to the E pole and the red contact pin is connected to the C pole, the instrument pointer may be deflected to some extent. For PNP tube, when the black stylus is connected to the C pole and the red stylus is connected to the E pole, the instrument pointer may be deflected to some extent, and vice versa. Therefore, the C and E poles of the triode can also be determined. However, this method is not suitable for high-pressure resistant pipelines.