How to do PCB circuit board inspection
1. Voltage measurement or when testing waveform with an oscilloscope probe, the test leads or probes should not be short-circuited between the pins of the integrated circuit due to sliding, and the measurement is performed on a peripheral printed circuit that is in direct communication with the pins. Any short circuit in any moment can easily damage the integrated circuit, and more care should be taken when testing flat-packaged CMOS integrated circuits.
2. It is not allowed to use soldering iron for welding. To confirm that the soldering iron is not charged, ground the soldering iron shell. Be careful with the MOS circuit. It is safer to use 6-8V low voltage circuit iron.
3. If it is necessary to add external components instead of the damaged parts inside the integrated circuit, small components should be selected, and the wiring should be reasonable to avoid unnecessary parasitic coupling, especially between the audio power amplifier integrated circuit and the preamplifier circuit. Ground terminal.
4. It is strictly forbidden to directly test the TV, audio, video and other equipment without power isolation transformer with the equipment that is grounded. Although the general tape recorder has a power transformer, when it comes to a special TV or audio device that has a large output power or a poor understanding of the nature of the power supply used, it is first necessary to find out whether the chassis of the machine is powered or not. The TV, audio and other equipment with the bottom plate are short-circuited by the power supply, affecting the integrated circuit, causing further expansion of the fault.
5. Before checking and repairing the integrated circuit, first familiarize yourself with the function of the integrated circuit used, the internal circuit, the main electrical parameters, the function of each pin, and the normal voltage of the pin, the waveform and the working principle of the components of the peripheral components. If the above conditions are met, analysis and inspection will be much easier.
6. Do not easily judge that the integrated circuit is damaged. Because most of the integrated circuits are directly coupled, once a certain circuit is abnormal, it may cause multiple voltage changes, which are not necessarily caused by integrated circuit damage. In some cases, the voltage of each pin is measured and normal. When the values match or are close, it does not necessarily mean that the integrated circuit is good. Because some soft faults do not cause a change in the DC voltage.