Technical
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Content of PCB incoming testing
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Testing Techniques for Common Electronics Components

The core of electronic equipment is the circuit board, and the circuit board is composed of a large number of various types of electronic components. If the equipment malfunctions or short-circuits, most of it is caused by the failure or damage of the electronic components. Today China PCBA manufacturer will bring you some correct component inspection techniques.

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

The multimeter is set to R×1k stall, the black test probe is connected to any pin of the rectifier bridge, and the red test probe is used to test the remaining three pins successively. If the reading is infinite, the black test probe is connected to the output positive pole of the bridge stack; if the reading is 4~10kΩ, the pin connected to the black test probe is the output negative pole of the bridge stack, and the remaining two pins are the AC input pin of the rectifier bridge.


2. Judge the quality of the crystal oscillator
First use a multimeter (R×10k stall) to measure the resistance value at both ends of the crystal oscillator. If the resistance value is infinite, it means that the crystal oscillator has no short-circuit or electric leakage; then insert the test pencil into the mains socket and pinch any pin of the crystal oscillator with your fingers, touch the other pin to the metal part on the top of the test pencil. If the neon bulb of the test pencil turns red, it means that the crystal oscillator is good; if the neon bulb doesn’t turn bright, it means that the crystal oscillator is damaged.

3. Unidirectional thyristor inspection

The R×1k or R×100 stall of a multimeter can be used to measure the forward and reverse resistance between any two poles. If the resistance of a pair of poles is found to have a low resistance value (100Ω~lkΩ), then the black test probe is connected to the control electrode, the red test probe is connected to the cathode, and the other is the anode. The thyristor has 3 PN junctions, and we can judge its quality by measuring the forward and reverse resistance of the PN junction. When measuring the resistance between the control electrode (G) and the cathode (C), if the forward and reverse resistances are both being zero or infinite, it indicates that the control electrode is short-circuited or break-circuited. When measuring the resistance between the control electrode (G) and the anode (A), both the positive and reverse resistance readings should be large; when measuring the resistance between the anode (A) and the cathode (C), both the positive and the reverse resistance should be large.

4. Polarity recognition of bidirectional thyristor

The bidirectional thyristor has a main electrode 1, a main electrode 2 and a control electrode. If the resistance between the two main electrodes is measured with a multimeter R×1k stall, the reading should be approximately infinite, and the positive and negative 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 test probe is connected to the main electrode 1 and the red test probe is connected to the control electrode, the measured forward resistance is always smaller than the reverse resistance. Therefore, we can easily identify the main electrode 1 and the main electrode 2 by measuring the resistance.

5. Check the quality of the light-emitting digitron
Firstly, set the multimeter to R×10k or R×100k stall, and then connect the red test probe to the "ground" leading-out terminal of the digitron (take the common cathode digital tube as an example), and the black test probe will connect to the other leading-out terminals of the digitron in turn. The seven segments should be illuminated separately, otherwise the digital tube is damaged.