SMT skills, 15 tips on how to detect the quality of electronic components

604 Published by FASTPCBA 7月 17,2018

A large number of electronic components of various types are used in electronic equipment. Most of the equipment failures are caused by the failure or damage of electronic components.Therefore, how to detect electronic components is particularly important, which is also a skill that electronic maintenance personnel must master.The following is some common electronic components inspection experience and skills compiled by jingbang electronics for your reference.
1. Measure the polarity of each foot of the rectifier bridge
Multimeter block set R x 1 k, black pens and any pins of the bridge pile, red pens and measured successively the remaining three legs, if the readings are infinite, the black pens and connect to the output of the bridge pile by the positive, if the reading is 4 ~ 10 k Ω, the black pens and the pin is the output of the bridge pile of the cathode, the rest of the two pins for bridge pile of ac input.
2. Judge the quality of crystal vibration
First, the resistance value at both ends of the crystal vibration is measured by the multimeter (R * 10k block). If it is infinite, it indicates that the crystal vibration has no short circuit or leakage.Then test pencil inserted in the mains socket, his fingers hold any pins of crystals, will touch another pin test pencil at the top of the metal parts, if the test pencil neon bulb is red, that crystals is good;If neon is not bright, the crystal vibration is damaged.
3. One-way thyristor detection
Available multimeter R x 1 k or R x 100 block measurement of positive and reverse the question of arbitrary polarization resistance, if it finds a pair of very resistance to low resistance (100 Ω to lk Ω), is for the control of the black pens and receive pole, red pens and connect to the cathode, another is the anode.Thyristor has three PN junction, we can judge its quality by measuring the positive and reverse resistance of PN junction.Measure control (G) and cathode (C) between the resistance, if the positive and reverse resistance are zero or infinity, that control is extremely short circuit or open circuit; measure control (G) and the anode resistance between (A), the positive and reverse resistance readings shall be great; {measure the anode and the cathode (A) (C) resistance, between the positive and reverse resistance should be large.
4. Polarity identification of two-way thyristor
Bidirectional thyristor has main electrodes 1, main electrodes 2 and control, if the multimeter R x 1 k in measuring the resistance between one of the two main electrodes, reading should be similar to infinity, and control and as a main electrode extremely positive and reverse resistance between reading only a few tens of Europe.According to this characteristic, it is easy to identify the control electrode of the thyristor by measuring the resistance between the electrodes.When the black stylus is connected to the main electrode 1.The positive resistance measured when the red pen is connected to the control electrode is always smaller than the reverse resistance, so it is easy to identify the main electrode 1 and the main electrode 2 by measuring the resistance.
5. Check the quality of the luminous digital tube
Multimeter first set R x 10 k or R x l00k block, then red pens and with digital tube (in Yin digital tube, for example) in “ground” terminal connected, black pens and other terminal digital tube, in turn 7 shall be respectively, otherwise shows that digital tube damage.
6. Identify the electrode of junction field effect tube
Puts multimeter R x 1 k block, with black pens and contact the pin grid G is assumed, and then use the red pens and contact the other two pins, respectively, if the resistance value are relatively small (5 ~ 10 Ω), will be red and black pens and exchange measure again.If the resistances are all large (infinity), it means that they are all reverse resistors (reverse PN junction), belonging to N channel pipe, and the pin of the black pen contact is grid G, indicating that the original assumption was correct.If the resistances measured again are small, it means that the forward resistors belong to the p-channel field effect pipe, and the black pen is connected with grid G.If the above situation does not occur, the red and black stylus can be replaced and tested by the above method until the grid is determined.General junction field-effect tube of the source and drain when manufacturing is symmetrical, so, when the grid G determine later, for the source and drain D S doesn’t have to, because the two can be used interchangeably.The resistance between the source and the drain is several thousand euros.
7. Triode electrode identification
For a type of unmarked or unmarked triode, a multimeter test can also be used to identify the three electrodes.First set the universal meter range switch on the R x 100 or R x 1k barrier.Red pens and any contact with an electrode triode, black pens and, in turn, contact with the other two electrodes, measured the resistance value between them, when were hundreds of the low resistance is measured, the red pens and contact electrodes are the base of b, the pipe for the PNP.If the high resistance is measured in tens to hundreds of thousands of euros, the electrode that the red stylus contacts is also base b, and this tube is NPN tube.
On the basis of identifying the tube type and base b, the collector is determined by using the principle that the forward current amplification coefficient of the triode is larger than that of the reverse current amplification coefficient.Assume either one electrode c or the other electrode e.Set the universal meter range switch on the R * 1k barrier.For: PNP tube, make the red stylus connect to the c pole, the black stylus connect to the e pole, and then pinch the b and c poles of the tube with your hand at the same time, but cannot make the b and c poles touch each other directly, and measure a certain resistance value.Then the second measurement of the two gauges was carried out, and the resistance measured was compared. For: PNP tube, the resistance value was small for the first time, and the collector electrode of the electric electrode of the red stylus was connected.For a small resistance value of the NPN tube, the electrode of the electrode collector connected by the black stylus.
8. Judge the quality of potentiometer
The nominal resistance of the potentiometer is measured first.Multimeter is ohm block on both ends of the “1”, “3” (a “2” for the activity contact), the readings shall be the nominal value of the potentiometer, such as multimeter pointer motionless, resistance or resistance differs a lot, indicates the potentiometer has been damaged.Then check whether the moving arm of the potentiometer is in good contact with the resistor.Multimeter is ohm block “1”, “2” or “2”, “3” on both ends, the potentiometer spin counterclockwise direction of rotation to close to the “off” position, the resistance should be as small as possible, and then slowly clockwise rotation handle, resistance should be increased gradually, spin to extreme position, the value should be close to the nominal value of the potentiometer.For example, when the shaft handle of the potentiometer rotates, the pointer of the universal meter has a jumping coracle.
9. Measure the leakage resistance of large capacity capacitors
Put the 500 type multimeter in R * 10 or R * 100 gear, and when the pointer points to the maximum value, immediately use R * 1k gear measure, the pointer will be stable in a short time, so as to read the resistance value of leakage resistance.
10. Identify infrared receiving head pins
Multimeter block set R x 1 k, first suppose to receive the head a foot as an earthing terminal, with the black pens and hung with red pens and resistance measured two foot, compared to two times the measured resistance (generally in the range of 4 ~ 7 kq), resistance smaller once its red pens and connect to + 5 v power supply pins, another resistance larger for signal pin.Conversely, if use red pens and pick up the known anchor, black pens and measured respectively and signal power supply the feet is known, the resistance value is above 15 k Ω, resistance of small pins for + 5 v, resistance to large pin for signal.If the measurement results meet the above resistance values, the receiving head can be judged to be in good condition.SMT skills
11. Determine the polarity of unsigned electrolytic capacitors
To short-circuit capacitance discharge, then two fuses will do A good job of A and B tag, multimeter set R * 100 or R * 1 k block, black pens and A lead, red pens and B lead, after being pointer stationary readings, measuring short circuit after discharge,Connect the black stylus to the B lead, and the red stylus to the A lead. Compare the two readings.
12. Light-emitting diode measurement
Take a capacity greater than 100 “F the electrolytic capacitor (capacity is larger, the more obvious phenomenon), use multimeter R x 100 first block to its charge, black pens and capacitor anode, red pens and connect the cathode, the charging is completed, the black pens and negative capacitance change, will be measuring leds and red pens and capacitance between the anode.If the led lights out gradually, it is good.At this point, the red pen is connected with the cathode of the light-emitting diode, and the capacitor is connected with the cathode of the light-emitting diode.If the light emitting diode is not bright, reconnect the two ends of the light emitting diode to the test. If it is not bright, the light emitting diode is damaged.
13. Photoelectric coupler detection
For the multimeter, the resistance R * 100 block is selected, and the resistance R * 10k block is not allowed, in case the battery voltage is too high to break the led.The red and black stylus are connected to the input terminals to measure the positive and reverse resistors. Normally, the forward resistance is dozens of ohms, and the reverse resistance is several thousand to dozens of ohms.If the positive and reverse resistors are similar, the led is damaged.Multimeter optional resistance R * 1 gear.The red and black stylus are connected to the output end to measure the positive and reverse resistance, which is close to infinity under normal conditions, otherwise, the optical tube will be damaged.Multimeter to choose R x 10 block, red, black pens and input and output respectively luminous tube measurement and by light pipe insulation resistance between the (conditional application of measuring the insulation resistance by megger are, at this time by megger output rated voltage should be slightly lower than allowed by metering electricity coupler pressure value), the luminous tube and asked by light pipe insulation resistance should be up properly.SMT skills
14. Detection of photosensitive resistance
The multimeter to R x 1 k Ω block, the photosensitive resistance smooth and keep the vertical incident light, and so on the multimeter directly measured resistance is light resistance.Put the photosensitive resistance in a completely dark place, then the resistance measured by the multimeter is the dark resistance.If the bright resistance is several thousand to dozens of dry ohms and the dark resistance is several to dozens of megaohms, the photosensitive resistance is good.SMT skills
15. Damage identification of laser diode
Remove the laser diode, measure, under normal circumstances reverse resistance should be infinity, positive resistance in 20 k Ω Ω ~ 40 k.If measured positive resistance has more than 50 k Ω, shows that laser diode performance has fallen;If its positive value has more than 90 k Ω, show that the tube is damaged, can no longer in use.SMT skills

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