June 29, 2019
3071
I will share some useful testing electronic components ways by analyzing 10 component testing and troubleshooting with tools and my experiences.
I will share ways on how to test electronic components with multimeter and how to troubleshooting during testing.
Let’s start.
First I will introduce component testing methods for 7 kinds of resistors. Details are as followed:
1. Fixed resistor testing
The actual resistance value can be test by connecting to the two ends of the resistor with the test leads (not positive or negative).
In order to improve the measurement accuracy, you can selected the measured range according to the nominal value of the measured resistance. If you want to make the measurement be more accuracy, you need to make pointer indication value falls as far as possible to the middle position of the scale, that is, within the range of 20% to 80% radians of the full scale. Why?
Because, the non-linear relationship of the ohmic scale, its middle section is finer. Please note: Depending on the level of resistance error. An error with ±5%, ±10% or ±20% is allowed between the reading and the nominal resistance, respectively. If it does not match and the error range is exceed, the resistance value is changed. Except the above, besides, when you are testing a fixed resistor, especially measuring resistors with resistance values above 10 kΩ, do not touch the conductive parts of the test leads and resistors.
2. Cement resistor testing
As we all know cement resistor is one of resistors with heat and flame retardant features.
You can also use test leads test or troubleshot for cement resistor. The test method is the same as fixed resistor.
3.Fuse resistor testing
In the circuit, when the fuse resistor is melted and disconnected, it can be judged based on experience:
If the surface of the fuse resistor is found to be black or burnt, it can be concluded that its load is too heavy, and the reason is current passing through it exceeds the rated value many times.
If the surface is open without any trace, it means that the current through is just equal to or slightly larger than its rated melting value. But judging whether the fuse resistor with no trace on the surface is good or not, you can measure by the multimeter R×1 block. To ensure accurate measurement, one end of the fuse resistor should be soldered from the circuit. If the measured resistance is infinite, the fuse resistor has failed to open. If the measured resistance is far from the nominal value, it indicates that the resistance value is not suitable for reuse.
Please note: In the maintenance practice, it is found that there are also a few blown resistors that are short-circuited in the circuit. You should pay attention when testing.
4. Potentiometer testing
When checking the potentiometer, first you need to turn the handle to see if the rotation of the handle is smooth, whether the switch is flexible, and whether the “click” sound is clear when the switch is turned on or off. Besides, you should listen to the sound of the internal contact point of the potentiometer and the friction of the resistor. If there is a “shasha” sound, the quality is not good. When testing potentiometer with a multimeter, you should choose a suitable electric blocking position for the multimeter, according to the resistance of the tested potentiometer.
Then test potentiometer as follows:
A: Use the ohmmeter of the multimeter to measure the "1" and "2" ends. The reading should be the nominal resistance of the potentiometer. If the pointer of the multimeter does not move or the resistance value is different, it indicates that the potentiometer is damaged.
B: How to heck if the movable arm of the potentiometer is in good connect with the resistor.
Here is a way: use the ohmmeter of the multimeter to check both ends of "1", "2" (or "2", "3"), and turn the rotary shaft of the potentiometer counterclockwise to the position close to "off".
In this time, the resistance values is smaller, the better. Then, rotate the shank slowly clockwise, the resistance value should be gradually increased, and the pointer in the meter should move smoothly. When the shank is turned to the extreme position "3", the resistance should be close to the nominal value of the potentiometer
If the pointer of the multimeter is bouncing during the rotation of the shaft handle of the potentiometer, it indicates that the movable connect has a fault of poor connect.
5. Positive temperature coefficient thermistor testing
When testing, use a multimeter R × 1, specifically can be divided into two steps:
A: Normal temperature detection (indoor temperature is close to 25 ° C); The two pins of the PTC thermistor are connected to the test leads to check the actual resistance, and compared with the nominal resistance, the difference between the two is within ±2 Ω. If the actual resistance is too different from the nominal resistance, it indicates poor performance or damage.
B: Heating test: On the basis of the normal temperature test, the second test can be carried out - heating detection.
Heat a heat source (such as a soldering iron)* near the PTC thermistor, and use a multimeter to monitor whether the resistance value increases with the increase of temperature. If so, the thermistor is normal. But if there is no change in the resistance value, the performance is deteriorated and cannot be used any more.
Please note: Be careful not to get the heat source too close to or directly in contact with the PTC thermistor to prevent it from being burnt.
6. Negative temperature coefficient thermistor testing
1) Measuring the nominal resistance value Rt
The method of measuring the NTC thermistor with a multimeter is the same as the method of measuring the ordinary fixed resistor.
That is, according to the nominal resistance of the NTC thermistor, the actual value of Rt can be directly measured by selecting an appropriate electrical barrier. However, since the NTC thermistor is very sensitive to temperature, the following points should be noted when testing:
A: Rt is measured by the manufacturer at an ambient temperature of 25 ° C, so when measuring Rt with a multimeter, it should also be carried out when the ambient temperature is close to 25 ° C to ensure the credibility 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. When testing, do not hold the thermistor body with your hands to prevent the body temperature from affecting the test.
2) Estimating the temperature coefficient αt
First, you need to measure the resistance value Rt1 at room temperature t1. Then use the electric iron as the heat source, near the thermistor Rt to measure the resistance value RT2.
At the same time, you need to use a thermometer to test the average temperature t2 of the surface of the thermistor RT at this moemnt, then calculated.
7. Varistor testing
Use the R×1k of the multimeter to measure the positive and negative insulation resistance between the two pins of the varistor, which are infinite. Otherwise, the leakage current is large.
If the measured resistance is small, the varistor is damaged and cannot be used.
8. Photoresistance testing
A: Use the black light film to cover the light-transmitting window of the photoresistor. At this time, the pointer of the multimeter is basically kept, and the resistance is close to infinity. The larger the value, the better the photoresistor performance. If this value is small or close to zero, the photoresistor has been burned through and can no longer be used.
B: Use a light source to align with the light-transmitting window of the photoresistor, then, the pointer of the multimeter should have a large amplitude swing, and the resistance value is significantly reduced.
The smaller the value, the better the photoresistor performance. If the value is large or infinite, it indicates that the open circuit of the photoresistor is damaged and cannot be used any more.
C: The light-receiving window of the photoresistor is aligned with the incident light, and the small black paper is shaken on the upper part of the light-shielding window of the photoresistor to be intermittently received by the light. At this time, the pointer of the multimeter should swing left and right with the shaking of the black paper. If the multimeter pointer is always stopped at a certain position and does not oscillate with the paper shake, it indicates that the photosensitive material of the photoresistor has been damaged.
9. Fixed capacitor testing
A: Testing small capacitors below 10pF: Because the fixed capacitor capacity below 10pF is too small. when testing capacitor with multimeter, you can only qualitatively check for leakage, internal short circuit or breakdown. When testing, you can use the multimeter R×10k, and connect the two pins of the capacitor with test leads. The resistance should be infinite. If the measured resistance value (the pointer swings to the right) is zero, the capacitor leakage is damaged or internal breakdown.
B: You can use Multimeter selects R×1k to check if the 10PF~0, 01μF fixed capacitor has a charging phenomenon, and then judge whether it is good or bad.
The beta values of the two triodes are all above 100 and the penetration current is small. You can use a composite tube of 3DG6 and other types of silicon triodes. The red and black test leads of the multimeter are 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 capacitor is enlarged to increase the multimeter pointer swing amplitude for observation.
But, you should noted that during the testing, especially when testing the capacitance of a small capacity, it is necessary to repeatedly exchange the measured capacitor pins to contact A and B points to clearly see the swing of the multimeter pointer.
C: For fixed capacitors above 0,01μF, the multimeter's R×10k can be used to directly test the capacitor for charging process and whether there is internal short circuit or leakage, and the capacity of the capacitor can be estimated according to the amplitude of the pointer swinging to the right.
10. Electrolytic capacitor testing
There are details about testing capacitors with multimeter.
A: Because the capacity of electrolytic capacitors is much larger than that of general fixed capacitors, the appropriate range should be selected for different capacities when testing. According to experience, under normal circumstances, the capacitance between 1 ~ 47μF can be measured by R × 1k , and the capacitance larger than 47μF can be measured by R × 100.
B: Connect the multimeter with red pen to the negative pole and the black gauge to the positive pole. When connecting, the multimeter pointer deflects to the right with a large degree of skewness (for the same electrical block, the larger the capacity, the larger the swing), then gradually turns to the left, finally it stops at a certain position. The resistance at this time is the forward 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 several hundred kΩ or more, otherwise, it will not work properly.
During testing, if there is no charging in the forward and reverse directions, that is, the hands are not moving, which means the capacity disappears or the internal circuit is broken; if the measured resistance is small or zero, the leakage of the capacitor is large or the breakdown is broken. Can no longer be used.
C: For an electrolytic capacitor in which the positive and negative signs are unknown, the above method for testing the leakage resistance can be used for discrimination. That is, first test the leakage resistance arbitrarily, remember its size, then exchange the test leads to test a resistance value. The one with a large resistance value in the two measurements is the forward connection method, that is, the black test lead is connected to the positive pole, and the red test lead is connected to the negative pole.
D: Using the multimeter resistance to test the capacity of the electrolytic capacitor according to the magnitude of the swing of the pointer to the right by the method of positively and inversely charging the electrolytic capacitor.
11. Variable capacitor testing
Here are 3 ways that you can test capacitors. Details are as followed:
A. Gently rotate the shaft by hand, it should feel very smooth, and should not feel sometimes loose or even stuck in normal situation. When the axial direction of the load is pushed forward, backward, up, down, left, right, etc., the shaft should not be loose.
B. Rotate the shaft with one hand and gently touch the outer edge of the group with the other hand. There should be no looseness. The variable capacitor with poor contact between the rotating shaft and the moving piece can no longer be used.
C. Place the multimeter in the R×10k. Connect one of the test leads to the output of the variable capacitor and the lead of the fixed piece with one hand. The other hand will slowly rotate the rotating shaft several times. The multimeter pointer should be Infinity position does not move.
In the process of rotating the shaft, if the pointer sometimes points to zero, it means there is a short circuit between the moving piece and the fixed piece; if it touches an angle, the multimeter reading is not infinite but a certain resistance value appears, indicating that the variable capacitor is moving. There is leakage between the film and the stator.
That all the electronic component testing I know for different capacitor and resistor. Except troubleshooting or testing electronic components with multimeter, you can also troubleshooting by your experience.
