How to check the quality of components? Sharing skills of detecting circuit board components

Date：2022-04-18 15:17:10 Views：1527

In the circuit, the components working in the state of high voltage, high current and high power undoubtedly bear great pressure and have great possibility of damage. At the same time, they are also the key components and functional components of the circuit. The core of electronic equipment is the circuit board, which is welded and assembled by various types of electronic components. If the equipment fails or has a short circuit, most of the reasons will be caused by the failure or damage of electronic components. How to check the quality of components? Share the skills of detecting the quality of circuit board components.

1. Measure the polarity of each pin of the rectifier bridge

Multimeter setting R × 1K gear, the black lead is connected to any pin of the bridge pile, and the red lead successively measures the other three pins. If the readings are infinite, the black lead is connected to the output positive pole of the bridge pile. If the readings are 4 ~ 10K Ω, the pin connected to the black lead is the output negative pole of the bridge pile, and the other two pins are the AC input end of the bridge pile.

2. Judge the quality of crystal oscillator

First use a multimeter (R × 10K block) measure the resistance value at both ends of the crystal oscillator. If it is infinite, it indicates that the crystal oscillator has no short circuit or leakage; Then insert the test pen into the mains socket, hold any pin of the crystal oscillator with your fingers, and touch the other pin with the metal part at the top of the test pen. If the neon bubble of the test pen is red, it indicates that the crystal oscillator is good; If the neon bubble is not bright, the crystal oscillator is damaged.

3. Unidirectional thyristor detection

R of available multimeter × 1K or R × Measure the forward and reverse resistance of any two poles at gear 100. If the resistance of a pair of poles is found to be low (100 Ω ~ LK Ω), then the black probe is connected to the control pole, the red probe is connected to the cathode and the other pole is the anode. The thyristor has three PN junctions. We can judge whether it is good or bad by measuring the forward and reverse resistance of PN junction. When measuring the resistance between the control electrode (g) and the cathode [C], if the forward and reverse resistance are zero or infinite, it indicates that the control electrode is short circuited or open circuited; When measuring the resistance between control electrode (g) and anode (a), the forward and reverse resistance readings should be large; {when measuring the resistance between anode (a) and cathode (c), the forward and reverse resistance should be large.

4. Polarity identification of bidirectional thyristor

The bidirectional thyristor has main electrode 1, main electrode 2 and control electrode. If a multimeter R is used × 1K gear measures the resistance between two main electrodes, and the reading should be approximately infinite, while the forward and reverse resistance readings between the control electrode and any main electrode are only tens of ohms. According to this characteristic, we can easily identify the control electrode of the bidirectional thyristor by measuring the resistance between the electrodes. When the black probe is connected to the main electrode 1. When the red probe is connected to the control electrode, the measured forward resistance is always smaller than the reverse resistance. Therefore, it is easy to identify the main electrode 1 and main electrode 2 by measuring the resistance.

5. Check the quality of the LED

Set the multimeter to r first × 10K or R × L00k block, and then connect the red probe with the "ground" leading out end of the nixie tube (taking the common cathode nixie tube as an example), and the black probe is connected with other leading out ends of the nixie tube in turn. The seven sections should emit light respectively, otherwise it indicates that the nixie tube is damaged.

6. Electrode for distinguishing Junction FET

Place the multimeter in R × 1K gear, use the black probe to contact the pin assumed to be grid g, and then use the red probe to contact the other two pins respectively. If the resistance values are relatively small (5 ~ 10 Ω), exchange the red and black probes for measurement once. If the resistance values are large (∞), it indicates that they are reverse resistance (PN junction reverse), belonging to n-channel tube, and the pin contacted by the black probe is grid g, which indicates that the original assumption is correct. If the resistance values measured again are very small, it indicates that it is a positive resistance, belonging to p-channel FET, and the black probe is also connected to grid G. If the above situation does not occur, the red and black probes can be replaced and tested according to the above method until the grid is judged. Generally, the source and drain of Junction FET are symmetrical during manufacturing. Therefore, when the grid G is determined, it is not necessary to distinguish the source s and drain D, because the two electrodes can be used interchangeably. The resistance between source and drain is thousands of ohms.

7. Measure the leakage resistance of large capacitance

Place the 500 Multimeter in R × 10 or R × Gear 100. When the pointer points to the maximum value, switch to R immediately × 1K gear measurement, the pointer will be stable in a short time, so as to read the leakage resistance value.

8. Identify infrared receiver pin

Multimeter setting R × 1K gear, first assume that a pin of the receiving head is the grounding terminal, connect it with the black lead, measure the resistance of the other two pins with the red lead respectively, and compare the resistance values measured twice (generally in the range of 4 ~ 7kq). For the one with small resistance, the red lead is connected to the 5V power pin, and the other with large resistance is the signal pin. On the contrary, if the red lead is connected to the known anchor and the black lead is used to measure the known power pin and signal pin respectively, the resistance value is above 15K Ω, the pin with small resistance value is 5V end, and the pin with large resistance value is signal end. If the measurement result conforms to the above resistance value, it can be judged that the receiving head is intact.

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