PCB Tech - 9 tips for PCB board inspection

1. It is strictly forbidden to use grounded test equipment to touch the live TV, audio, video and other equipment of the bottom plate to test the PCB board without an isolation transformer

2. Pay attention to the insulation performance of the soldering iron when testing the PCB board

It is not allowed to use a soldering iron for soldering with power. Make sure that the soldering iron is not charged. It is best to ground the shell of the soldering iron. Be more careful with the MOS circuit. It is safer to use a low voltage soldering iron of 6~8V.

3. Before testing the PCB board, understand the working principle of integrated circuits and related circuits

Before inspecting 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, and the normal voltage of the pin, the waveform and the working principle of the circuit composed of peripheral components. If the above conditions are met, analysis and inspection will be much easier.

4. Do not cause short circuit between pins when testing the PCB board

When measuring voltage or testing the waveform 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. It is best to measure on the peripheral printed circuit directly connected to the pins. Any momentary short circuit can easily damage the integrated circuit. You must be more careful when testing flat-package CMOS integrated circuits.
5. The internal resistance of the PCB board test instrument should be large

6. Pay attention to the heat dissipation of the power integrated circuit when testing the PCB board

The power integrated circuit should have good heat dissipation, and it is not allowed to work in a high-power state without a heat sink.

7. To detect the PCB board leads should be reasonable

If it is necessary to add external components to replace the damaged part of the integrated circuit, small components should be selected, and the wiring should be reasonable to avoid unnecessary parasitic coupling, especially the grounding between the audio power amplifier integrated circuit and the preamplifier circuit end.

8. The quality of soldering must be ensured when testing PCB boards

When soldering, the solder is firm, and the accumulation of solder and pores are likely to cause false soldering. The soldering time is generally no more than 3 seconds, and the power of the soldering iron should be about 25W with internal heating. The integrated circuit that has been soldered should be carefully checked. It is best to use an ohmmeter to measure whether there is a short circuit between the pins, confirm that there is no solder adhesion, and then turn on the power.

9. Do not judge the damage of the integrated circuit easily when testing the PCB board

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