Circuit board assembly fault judgment and detection methods

The core of the electronic technology equipment is the circuit board, and the circuit board is assembled by a variety of different types of electronic components for welding, if the enterprise equipment between the failure of the problem or there is no short-circuit, the cause of most of them will appear in the Chinese electronic components failure or damage caused by.

1. Measure the polarity of each leg of the bridge

The multimeter is set to R x 1k, the black chanter is connected to any one pin of the bridge stack, and the red chanter measures the other three pins in turn. If the reading is infinity, the black stylus is connected to the output positive pole of the bridge stack; if the reading is 4 ~ 10kΩ, the black stylus is connected to the output negative pole of the bridge stack,1oz vs 2oz Copper and the other two pins are the AC input of the bridge stack.

2. Judge the crystal oscillator good or bad

First, use a multimeter (R × 10k block) to measure the resistance value at both ends of the crystal oscillator. If the resistance value is infinite, this means that the crystal oscillator is not shorted or leaking, touch the other pin to the metal part at the top of the pencil. If the neon bulb turns red,how to test pcb board with a multimeter the crystal oscillator is good. If the neon bulb does not light up, the crystal oscillator is damaged.

3. Unidirectional thyristor test

The positive and negative resistance between any two poles can be measured with a R×1k or R×100 block multimeter. If you find a pole resistance is low (100ω ~ lkω), the black stylus connected to the control electrode, red stylus connected to the cathode, the other pole connected to the anode. The thyristor has three PN junctions, and we can judge the goodness of the PN junction by measuring the forward and reverse resistance. Measure the resistance between the control electrode (G) and the cathode (C), if the forward and reverse resistance is zero or infinity, it means that the control electrode is short-circuited or open-circuited; measure the resistance between the control electrode (G) and the anode (A), the positive and negative resistance readings should be large; measure the resistance between the anode (a) and the cathode (c), the forward and reverse resistance should be very large.

4. Bidirectional control thyristor polarity to identify

A thyristor has main electrode 1, main electrode 2 and control electrode. If the resistance between the two main electrodes is measured with a multimeter R × 1k, the reading should be close to infinity, and the positive and negative resistances between the control electrodes and any of the main electrodes should read only a few tens of euros. Based on this property, the control pole of a thyristor can be easily identified by measuring the resistance between the electrodes. And when the black table pen is connected to the main electrode 1. The positive resistance measured when the red meter is connected to the control electrode is always less than the reverse resistance, so the main electrodes 1 and 2 can be easily identified by measuring the resistance.

5. Check the quality of the LED.

First of all, the multimeter R × 10k or R × L00K group, and then the red watch pen and the digital tube (for example, ordinary shaded digital tube) "ground" export terminal connection, black watch pen connected to the digital tube in turn to the other export terminals, the seven segments should be light, otherwise the digital tube is damaged.

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