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How to do circuit board inspection work?

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Update time : 2020-06-05 14:01:00
1. When measuring voltage or testing waveforms with an oscilloscope probe, do not cause a short circuit between the pins of the integrated circuit due to sliding of the test leads or probes, and measure on the peripheral printed circuit directly connected to the pins. Any instantaneous short circuit is easy to damage the integrated circuit, and more care should be taken when testing flat-pack CMOS integrated circuits.
2. It is not allowed to use a soldering iron for welding. It is necessary to confirm that the soldering iron is not charged, ground the shell of the soldering iron, and pay more attention to the MOS circuit. It is safer to use a 6-8V low-voltage circuit iron.
3. If it is necessary to add peripheral components to replace the damaged parts inside the integrated circuit, small components should be used, and the wiring should be reasonable to avoid unnecessary parasitic coupling, especially to deal with ground terminal between audio power amplifier integrated circuit and preamplifier circuit
4. It is strictly forbidden to directly test the TV, audio, video and other equipment without power isolation transformer with instruments and equipment whose shell is grounded. Although general radio cassette recorders have power transformers, when you come into contact with a special TV or audio equipment that has a large output power or does not know the nature of the power supply used, you must first find out whether the chassis of the machine is charged, otherwise it is easy to cause a short circuit of the power supply to the TV, audio and other equipment with the bottom plate charged, which will affect the integrated circuit and cause the fault to further expand.
5. Before checking and repairing the integrated circuit, you must first be familiar with the function of the integrated circuit used, the internal circuit, the main electrical parameters, the role of each pin, the normal voltage of pin, waveform and working principle of the peripheral components circuits. If the above conditions are met, analysis and inspection will be much easier.
6. Do not easily judge that the integrated circuit is damaged. The vast majority of integrated circuits are directly coupled. Once a circuit is abnormal, it may cause multiple voltage changes, and these changes are not necessarily caused by damage to the integrated circuit. In addition, in some cases, when the measured voltage of each pin is consistent with or close to the normal value, it may not necessarily mean that the integrated circuit is good. Because some soft faults will not cause changes in DC voltage.
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