BASIC ELECTRONIC-BASIC COMPONENTS DETECTION METHODS

Components of the detection is an appliance repair basics, how to accurately and effectively detect the components of the relevant parameters to determine whether components of the normal, not a stereotyped thing, must be based on different components use different methods to determine components of normal or not. Especially for beginners, proficiency testing methods commonly used components and experience is necessary, the following test on the common experience of electronic components and test methods are introduced for the right.

1, resistor detection methods and experience:



1  fixed resistor testing. A  the two tables document (regardless of positive and negative) were the two ends of pin-phase with the resistance can be measured by actual resistance. To improve the measurement accuracy, the measured resistance should be based on the size of the nominal value selection range. As the scale of the nonlinear Ohm's block, it's the middle of a more sophisticated indexing and should therefore be directed to the pointer value fell as much as possible the middle scale position, that is, the start of full scale of 20% to 80% within the arc to make the measurement more accurate. According to different level of resistance error. Reading between the nominal resistance were allowed ± 5%, ± 10% or ± 20% errors. If not match, beyond the error range, it indicates that the value of a variable resistance value. B  Note: the tests, particularly in measuring the resistance of several kΩ resistance above, the hands do not touch the table pen and resistance of the conductive part; be detected resistance welding down from the circuit, at least to open a welding head, in order to avoid circuit The other components impact on the test, resulting in measurement error; color ring the resistance to Israel, although the signs to determine the ring, but is best when used with a multimeter to test the actual resistance.

2  cement resistance testing. Detection of resistance of cement with the testing methods and precautions identical ordinary fixed resistor.

3  fuse resistors test. In the circuit, open circuit when the fuse resistor fuse, may make judgments based on experience: if found to fuse resistors or charred black surface, it can be concluded that the overloaded by more than its current rating due to many times; If the surface without any trace of the open circuit, this indicates that the current flowing through exactly equal to or slightly larger than its rated fuse value. For the surface without any trace of fuse resistors to judge good and bad, can make use multimeter to measure the R × 1 block, in order to ensure measurement accuracy, should fuse resistors from the circuit on one end of the next weld. If measured resistance is infinite, then illustrate failure of fuse resistors are open, if the measured resistance falls far short of the nominal value, that value of resistance change, we should not be used. Maintenance practices found that a small number of fuse resistors in the circuit is short-circuit breakdown phenomena, testing, also should be noted.

4  potentiometer detection. Check potentiometer, the first rotating handle to turn and see rotating handle rotation is smooth, the switch is flexible, Switch On, on and off, "a click" sound is crisp, and hear potentiometer and the resistance of the contact point within the body of friction sound, if "imperfections" sound, indicating poor quality. Test with a multimeter first potentiometer resistance according to the size of the measured, select the appropriate resistance gear good multimeter, and then the following method can detect.

A  measured with a multimeter ohm block "1", "2" ends, the reading shall be nominal potentiometer resistance, such as the multimeter pointer difference between the number of fixed or resistance, is that the potentiometer has been corrupted.

B  testing activities potentiometer contact arm and the resistance film is good. Measured with a multimeter ohm file "1", "2" (or "2", "3") ends of the potentiometer shaft counter-clockwise rotation to close by the "off" position, then the smaller resistance the better. Handle clockwise rotation axis and then slowly, the resistance value should be increased gradually, first in the pointer table should be a smooth move. When the spin axis to handle the extreme position "3", the resistance should be close to the nominal value potentiometer. Such as the multimeter pointer in the handle potentiometer shaft rotation in the process of beating phenomenon, indicating a poor contact contact fault activity.

5  positive temperature coefficient thermistor (PTC) detection. Detection, with a multimeter R × 1 block, concrete can be two-step operation: A  room temperature test (room temperature close to 25 ℃); the two tables document contact with the two pin PTC thermistor to detect the actual resistance, and with Nominal impedance contrast, the two difference shall be within the ± 2Ω normal. If the actual resistance and nominal resistance value difference is too large, it indicates its performance is bad or damaged. B  heat detection; at room temperature tests are normal, based on the second step can be tested - heating tests will be a heat source (such as electric iron) near the PTC thermistor to its heating, while monitoring its resistance with a multimeter it increases with increasing temperature and, if so, shows normal thermal resistance, if resistance did not change, indicating deteriorating performance can not continue to use. Be careful not to heat with the PTC thermistor by too close, or direct contact with the thermistor in order to prevent the scorch.

6  negative temperature coefficient thermistor (NTC) of the test.
(1), measured nominal resistance value Rt
NTC thermistor with a multimeter measuring methods and measuring the same way as ordinary fixed resistor, which according to the nominal resistance of NTC thermistor select the appropriate power block can be directly measured actual value of Rt. But NTC thermistor is very sensitive to temperature, so testing should note the following: A  Rt is a manufacturer of environmental temperature measured at 25 ℃, so the measure with a multimeter Rt should also be at ambient temperature when close to 25 ℃, in order to ensure the credibility test. B  measured power shall not exceed the specified value, so that the current measurement error caused by thermal effects. C  attention to proper operation. Test, not to hand and hold the thermistor body to prevent body temperature impact on the test.
(2), estimate the temperature coefficient αt
First measured at room temperature under t1 resistance Rt1, electric iron to heat again, close to the thermistor Rt, measure the resistance RT2, also measured with a thermometer at this time the surface of the thermistor RT and then calculated the average temperature t2.

7  varistor testing. With a multimeter R × 1k varistor block measurement is between two pins, reverse insulation resistance, are infinite, otherwise, shows a large leakage current. If the measured resistance is small, indicating varistor is damaged, can not be used.

8  photosensitive resistance testing. A  black paper with a translucent window to cover the photosensitive resistor, multimeter pointer then remained fixed, resistance approaching infinity. This value shows the bigger the better the performance photosensitive resistance. If this value is very small or near zero, indicating photosensitive resistor has burn damage, can not continue to use. B  to align a light transmittance photoresistors window, then the target should be more substantial multimeter swing, resistance decreased significantly. Note that this value is smaller the better the performance of photosensitive resistance. Infinity If this value is great or even that the internal resistance of open photosensitive damage, could no longer continue to use. C  the photosensitive resistor aligned incident light transmittance window with black paper shade windows in the upper photosensitive resistance shaking, it stopped by the light, this time with the black pieces of paper multimeter pointer should be the rock and from side to side. If the multimeter pointer location does not always stop with the paper in a rock and swing, indicating resistance of the photosensitive photosensitive materials have been damaged.

Second, detection methods and experience of the capacitor

1  fixed capacitor test
A  detect small capacitance below 10pF
10pF capacitors due to the following fixed capacity is too small to measure with a multimeter can only check whether there are qualitative leakage, an internal short circuit or breakdown phenomenon. Measurements may make use of multimeter R × 10k block, with two tables document were two random access pin capacitance, resistance should be infinite. If the measured resistance value (a pointer to the right swing) is zero, it indicates damage to capacitor leakage or internal breakdown. B  detection 10PF ~ 0  01μF capacitors have charged a fixed phenomenon, which determine the good or bad. Multimeter used R × 1k block. 2 Transistor β values are above 100, and the tunneling current to be small. Optional 3DG6 silicon transistor models such as the composition of composite pipe. Multimeter's red and black table document separately with composite pipe collector emitter e and c phase. As the composite triode amplification, the measured charging and discharging of capacitors to be enlarged, so that the pointer put multimeter range to increase, thus easy to observe. It should be noted: In the test operation, especially in the smaller capacity of the capacitance measured when the measured capacitance pin to repeatedly swap contacts A, B two points clear to see that the multimeter pointer to swing. C  0  01μF or more for a fixed capacitance, the R × 10k multimeter can be used directly to test block capacitor charging process and whether within or without short-circuit or leakage, and according to the size of a pointer to the right swing of the magnitude estimated capacitances.

2  testing electrolytic capacitors
A  because the electrolytic capacitor is much greater than the average fixed capacitor, so measurements should be suitable for use in different capacity range. Experience, under normal circumstances, 1 ~ 47μF capacitor between, can be R × 1k block measurement, greater than 47μF capacitance measurement can be R × 100 block.
B  the multimeter red table document connected with negative, positive black table document access in new to the moment, multimeter pointer deflection is greater skewness to the right (for the same power block, the greater the capacity, the greater the swing), then gradually to the left turn, until the stop at a certain location. At this point the resistance is positive electrolytic capacitor leakage resistance, this value is slightly larger than the reverse leakage resistance. Practical experience show that the electrolytic capacitor leakage resistance should normally be more than several hundred kΩ, otherwise, will not work. In the test, if positive, no charge reverse phenomenon, that gauge needles do not move, it indicates the capacity disappeared or internal circuit; If the measured resistance value is small or zero, indicating a large capacitor leakage or breakdown damage can no longer use. C  for the positive and negative signs unknown electrolytic capacitors can be measured using the above method to determine leakage resistance. The first look at any measure leakage resistance, keep in mind the size, and then exchange the table document a resistance measured again. Twice that measured in a large resistance is connected in a positive, that the black table document access is positive, red table document then is negative. D  use multimeter power block, to the electrolytic capacitor is used, the reverse charge method, according to the size of a pointer to the right swings, can be estimated from the capacity of electrolytic capacitors.

3  detection of variable capacitor
A  gently rotating shaft, should feel very smooth and should not feel tight and sometimes loose even when the cable wiring. Will contain the axial front, back, up, down, left, right, etc. to promote in every direction, the shaft should not be loose phenomenon. B  rotating shaft with one hand, one hand moving film set light touch the outer edge, should not feel any loosening. Poor contact between the shaft and moving piece of variable capacitor, can not continue to use. C  be placed in R × 10k Multimeter block, the two tables to pen a hand pick each piece variable capacitor and fixed film fixed terminal, the other hand to slowly rotating shaft a few back and forth, multimeter pointer are infinite position should be fixed. In the rotating shaft of the process, if the pointer sometimes point to zero, which evidences that exist between films and short films set point; if you encounter a particular point of view, multimeter reading is not infinite but have certain resistance, indicating dynamic variable capacitor between the film and the stator leakage phenomenon.

3, inductors, transformers, test methods and experiences

1  color code inductor test
The multimeter put R × 1 block, red, black tables to pen the color code inductor connected either terminal, then the pointer should swing to the right. According to the resistance value measured the size of the specific points can be distinguished the following three conditions:
A  measured inductor resistance color code value is zero, the internal short-circuit failure. B  color code measured the size of the inductor DC resistance and wound inductor coil used enameled wire diameter, number of laps around the system has a direct relationship between the measured resistance as long as the value of the measured color code can be considered normal inductor of.

2  in transformer testing week
A  the multimeter to the R × 1 block allocated in accordance with the windings of the transformer in one week alignment of pins, one by one checking off the windings of the situation, to judge that is normal. B  testing insulation
Will be placed in R × 10k Multimeter block, do the following several state test:
(1) between the primary winding and secondary winding resistance value;
(2) the primary winding and the resistance between the shell;
(3) secondary winding and the resistance between the shell.
The test results are three situations occur:
(1) resistance to infinity: normal;
(2) zero resistance: a short circuit failure;
(3) resistance less than infinite, but greater than zero: a leakage failure.

3  power transformer testing
A  by observing the appearance of the transformer to check whether there are significant anomalies. Such as the coil wire is broken, loose soldering, insulation materials have burnt marks, whether the core fastening screw loose, whether silicon steel corrosion, such as winding coils have exposed. B  insulation test. R × 10k block with a multimeter were measured core and primary, primary and the secondary, core and the secondary electrostatic shield and panties secondary, secondary resistance between the windings, multimeter pointer should not refer to infinity position action. Otherwise, the shows bad transformer insulation. C  coil off of the test. Will be placed in R × 1 block multimeter, test, if a winding resistance value infinite, then shows a circuit of this winding fault. D  early identification, secondary coil. Power transformer primary and secondary pins pins were generally leads from both sides, and marked with a 220V primary winding and more words, the secondary winding is marked rated voltage value, such as 15V, 24V, 35V and so on. Identification based on these markers. E  load current detection. (A)  direct measurement. All the secondary winding open to all, put the multimeter AC current block (500mA, the primary winding in series. When the primary winding of the plug into 220V AC power, the multimeter is indicated by the value of load current. This value should not be transformer full load current is greater than 10% to 20%. The most commonly normal power transformers in electronic equipment should be 100mA load current is about. If beyond that, it indicates a short circuit of transformer failure. (b)  indirect measurement. In transformer primary winding in series with a 10  / 5W resistor, the secondary is still all empty. the multimeter to AC voltage block allocation. added power, you use two tables to pen measure the voltage drop across resistor R U, and then use Ohm's law calculate the load current I empty that I empty = U / R. F  load voltage detection. will take 220V power transformer primary electricity, then followed with a multimeter measuring AC voltage of each winding no-load voltage (U21 , U22, U23, U24) should meet the requirements value is generally permissible error range: high-voltage winding ≤ ± 10%, low-voltage windings of ≤ ± 5%, with a center tap of the two symmetrical winding voltage difference should be ≤ ± 2%. G  generally allow low-power power transformer temperature is 40 ℃ ~ 50 ℃, if the use of good quality insulating materials, allowing temperature also increased. H  detection determine the end winding of the same name. in the use of power transformers, sometimes in order to get required secondary voltage can be two or more secondary windings connected in series to use. used in series when using the power adapter to participate in series of the same name each winding must be properly connected client can not be wrong. Otherwise, the transformer can not be normal work. I. power transformer short-circuit failure of the comprehensive test discrimination. power transformer short-circuit failure occurred after the main symptoms are fever and severe secondary winding output voltage is abnormal. Typically, the coil turn to turn short circuit within the more points the more short-circuit current large, while the Transformer fever is more severe. test to judge whether the power transformer short-circuit failure of the simple method is to measure the load current (test methods have been introduced earlier). there is short-circuit fault of the transformer, the load current value can be greater than full load current 10%. When a serious short circuit, the transformer no-load power-in hundreds of seconds after the heat will be quickly, touching a hot iron core will be feeling. At this point can be determined without measuring current transformers are no-load short-circuit spots.