Ultrasonic plastic welding machine repair and home appliances repair. How accurately and effectively detect components of the relevant parameters, determine the components of the normal, not a follow the same pattern of it, according to different components using different methods, so as to judge the components of the normal or not.Especially for beginners, proficiency in commonly used components of the detection methods and experience is necessary, the following to commonly used electronic components test experience and method was introduced for the exam.

A resistor, the test methods and experience:

In 1, the detection of fixed resistors.A will be two meter (or negative) respectively, and the two ends of the resistance is connected with the pin can determine the actual value of the resistance.In order to improve the measurement precision, should be based on the measured resistance to the nominal value range of sizes to choose from.As a result of ohmmeter scale nonlinear relation, its middle section dividing the more sophisticated, so should make the indicator values as possible to scale the midsection position, i.e. full scale starting 20% to 80% radian range, in order to make the measurement more accurate.According to the different level of resistance error.Reading and nominal resistance respectively allow ± 5%, ± 10% and ± 20% error.If not consistent, beyond the range of error, the resistance value of the variable value.B note: test, especially in the measurement of dozens of more than k Ω resistor, hands do not touch the pen and resistance of the conductive portion; the detected resistance from the circuit of welding down, at least to welding a head, so as to avoid the circuit to other elements of the influence on the test result, measurement error; color ring resistance value although with color mark to determine, but when in use it would be best to use multimeter to test its actual value.

2, cement resistance detection.Detection of cement resistance method and the matters needing attention and detection of ordinary fixed resistor exactly the same.

In 3, fuse resistors detection.In the circuit, when the fuse resistor fuse open, according to the experience of judgment: if the fuse resistor surface blackening or burned, it can be concluded that the overload, through which the current exceeds a rated value caused by many times; if the surface without any trace and open, indicates that the current flowing through it is equal to or slightly greater than that of its rated fuse value.For the surface without any traces of fuse resistors to judge, but with Multimeter R × 1 block to measure, in order to ensure accurate measurement, the fuse resistor one end from the circuit of welding.If the measured resistance is infinite, then this fuse resistors have failure of open circuit, if the measured value and the nominal value differs very far, suggesting resistance value, also should not use.The repair practice, there are few fuse resistor in the circuit by short circuit breakdown phenomenon, testing should also be attention.

In 4, the detection of potentiometer.Check potentiometer, first of all to rotating the handle, handle rotation have a look whether smooth, switch is flexible, switch off, "click" sound is ringing, and listen to the potentiometer resistor internal point of contact and friction sound, such as "rustle" sound, explain quality is not good.With a multimeter test, according to the measured value of the potentiometer, selecting multimeter suitable resistance gear, then according to the following methods for detection.A multimeter ohmmeter test "1", "2" ends, the readings for potentiometer nominal resistance value, such as multimeter pointer does not move, or the resistance value is a lot of difference, that the potentiometer has been damaged.B detection of arm and the potentiometer resistor contact is good.With a multimeter measuring the ohm grade of "1", "2" (or "2", "3") ends of the rotating shaft of the potentiometer, counterclockwise rotation to close to the "off" position, then the resistance value of the smaller the better.Then slowly clockwise rotating shaft and handle, resistance should be increased gradually, the pointer should move smoothly in header.When the handle is screwed to the extreme position "3", the value should be close to the nominal value of potentiometer.If the pointer Multimeter in the potentiometer shaft during rotation of the beating phenomenon, indicating the activity contacts have poor contact fault.

5, the positive temperature coefficient thermistor (PTC) detection.When detecting, with a multimeter R × 1 block, concrete can be divided into two steps: A room temperature detection (indoor temperature is close to 25 DEG C); two pen contact PTC thermistor to detect the actual resistance of two pins, and compared with nominal resistance, the difference of the two is within ± 2 Ω is normal.If the actual value and the nominal value difference is too large, then its performance is bad or damaged.B temperature detection; in normal temperature test on a normal basis, then the second step test, temperature detection, a heat source (such as electric soldering iron) near the PTC thermistor for heating, while using a multimeter to monitor its resistance value is increased with temperature, such as is normal, indicating thermistor, if the resistance no change, to illustrate its performance deterioration, cannot continue to use.Take care not to make the heat source and the PTC thermistor by too close or direct contact thermal resistance, to prevent its spoil.

In 6, negative temperature coefficient thermistor (NTC) detection.(1), measuring the resistance of Rt multimeter is used to measure the NTC thermistor method and measuring general fixed resistor and the method of the same, according to the NTC thermistor nominal resistance value selection of suitable resistance block can directly measure the actual values of Rt.But because the NTC thermistor is very sensitive to temperature, so the test should pay attention to the following points: ARt is the manufacturer at an ambient temperature of 25 ℃ measured, so the multimeter is used to measure Rt, also should be near the ambient temperature 25 ℃, to ensure the credibility of the test.B measurement of the power shall not exceed the specified value, so as to avoid the current heat effect caused by measurement error.Pay attention to the correct operation of C.During the test, do not use hand pinch the thermistor body, to prevent the human body temperature have influence on the test.(2), estimation of temperature coefficient T first at room temperature T1 measured resistance value Rt1, then the electric soldering iron is used as a heat source, close to the Rt thermistor, measure the resistance value RT2, and measured with the thermometer at the thermistor RT mean surface temperature of T2 calculated again.

7, pressure sensitive resistance test.With a multimeter R × 1K gear measuring varistor two pin between the positive, reverse insulation resistance, are infinite, otherwise, leak current.If the measured resistance is very small, illustrate the varistor is damaged, can not be used.

8, photosensitive resistance test.A used a black card and the photosensitive resistance of transparent window cover, then the pointer multimeter remained motionless, resistance to infinity.This value is bigger shows the better performance of photosensitive resistance.If the values are very small or close to zero, description of photosensitive resistance has burned through damage, can not be used again.B will be a light against the photosensitive resistance of transparent window, then the pointer multimeter should greatly swing, resistance is obviously reduced.This value is the novel Akiko Min resistance performance.If the value of great or even infinite, that of photosensitive resistance internal open-circuit damage, also cannot again continue to use.C photosensitive resistance transparent window on the admittance of rays, with little pieces of paper on the photosensitive resistance shade window upper swing, which interrupted by light, the multimeter pointer should with black paper swing swing.If a multimeter pointer always stop at a position along with the disc swing swing, description of photosensitive resistance photosensitive material has been damaged.

Two, capacitor test methods and experience

1, fixed capacitor test.A detection of 10pF following small capacitance due to 10pF below the fixed capacitor capacity is too small, the multimeter to measure, only qualitative check whether there is leakage, internal short-circuit or breakdown phenomenon.When measuring, may choose to use multimeter R × 10K block, two pen respectively arbitrary connected capacitor two pins, the value should be infinite.If the measured resistance (pointer swinging to the right) is zero, the capacitor leakage damage or internal breakdown.B detection of 10PF ～ 001 μ F fixed capacitor is charging phenomenon, and judge its quality.Multimeter use R × 1K block.Two triodes β values were above 100, and a through current to small.You can select the 3DG6 type silicon transistor composite tube.Multimeter red and the black one is respectively connected with the composite emitter and collector C E.As a result of a compound triode amplification, the measured capacitor charge-discharge process be magnified, the meter pointer swing amplitude is increased, thereby facilitating the observation.It should be noted: in the test operation, especially in the measurement of small capacitance, to repeatedly change detected capacitor pin contact A, B two, can clearly see the multimeter pointer swing.C for 001 μ F above a fixed capacitor, available multimeter R × 10K gear test capacitor is charging process and has no internal short circuit or leakage, and according to the pointer swinging to the right extent size estimate capacitor capacity.

2, electrolytic capacitor test.A for electrolytic capacitor capacity than the general fixed capacitor is much larger, therefore, measurement, different capacity selection of suitable range.According to the experience, in general, 1 ～ 47 μ F capacitance between R × 1K gear measuring, available, more than 47 μ F capacitor available R × 100 gear measurement.B multimeter red one to the black one is connected to the positive electrode, negative electrode, at the moment, multimeter pointer deflection larger right skewness (for the same electrical barrier, the larger capacity, swing is larger), then gradually left rotation, until the stop at a position.This resistance is electrolytic capacitor positive leakage resistance, this value is slightly larger than the reverse leakage resistance.Actual experience shows that, electrolytic capacitor leakage resistance should be in general more than hundreds of K Ω, otherwise, will can not work regularly.In the test, if positive, reverse all without charging phenomenon, that hand does not move, the capacity to disappear or internal circuit; if the measured resistance is very small or zero, illustrate the capacitor leakage big or breakdown, can not be used again.C  for positive, negative sign of unknown electrolytic capacitor, the measurement of leakage resistance method to distinguish.First, any check leakage resistance, remember its size, and then exchange the pen to measure a resistance.Two measurements of large resistance of that time is the positive connection method, namely the black one is then positive, red table document connected is negative.D  use multimeter resistance block, the electrolytic capacitor is, reverse charging method, according to the pointer swinging to the right size, can estimate the electrolytic capacitor capacity.

In 3, a variable capacitor for the detection of A gently rotating shaft, should feel very smooth, should not feel sometimes disengagement even card hysteresis phenomenon.Will carry forward, after shaft, upper and lower, left, right and so on each direction rotating shaft drive, should not be loosen phenomenon.B rotating shaft with one hand, another hand to touch the rotor rim, should not feel any loosening phenomenon.The rotating shaft and the movable contact between the chip side of the variable capacitor, is unable to continue to use the.C Multimeter in a R × 10K block, a hand the two probes are respectively connected with the variable capacitor of the rotor and a stator terminal, on the other hand slowly rotating shaft a few back and forth, multimeter pointer must be infinite position.In the rotating shaft in the process, if the pointer sometimes point to zero, that exists between the rotor and a stator short-circuit point; if a certain angle, the multimeter reading is infinite but a certain resistance, explain variable capacitor between the rotor and stator leakage phenomenon.

Three, inductors, transformers test methods and experience.

1, color code inductor of detection the multimeter in the R x 1 block, red, black pen of the color code inductor any terminal, the pointer should swinging to the right.According to the measured resistance value, given the following three conditions were identified: A measured color code inductor resistance value is zero, the internal short circuit fault.B measured color code inductor DC resistance values and winding inductor coil by the enameled wire diameter, winding loop number directly, as long as it can measure the resistance value, it may be considered that the measured color code inductor is normal.

2, in week transformers detection A multimeter dial to R × 1 block, according to the week of transformer windings are arranged regularly check pins, each winding of the on-off state, and then determine whether normal.B detection of insulating performance of the multimeter in a R × 10K block, do the following several state test: (1) the primary winding and the secondary winding resistance value between the primary winding; (2) between the enclosure and the resistance value; (3) the secondary winding and the shell between the resistance value.The test result to occur in three situations: (1) the resistance is infinite: normal; (2) resistance to zero: short circuit fault; (3) value less than infinity, but greater than zero: leakage fault.

In 3, the detection of power transformer A by observing the transformer appearance to check whether the obvious anomalies.If the coil lead wire is broken, unsoldering, insulation materials are signs of burning, core fastening screw is loose, silicon steel sheet has no corrosion, the windings are exposed