A complete PCB board needs to go through many processes from design to finished product. When all the processes are in place, it will eventually enter the inspection link. Only the tested PCB boards will be applied to the product, so how to do the PCB circuit board inspection work , This is a topic that everyone is very concerned about. The following editor of Jinhong Circuit will tell you about the relevant knowledge of circuit board testing!
1. 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 lead or probe, and measure on the peripheral printed circuit directly connected to the pin. Any momentary short circuit can easily damage the integrated circuit. You must be more careful when testing flat-package CMOS integrated circuits.
2. It is not allowed to use a soldering iron for soldering with power. Make sure that the soldering iron is not charged. Ground the shell of the soldering iron. Be careful with the MOS circuit. It is safer to use a 6-8V low-voltage circuit iron.
3. If you need to add external components to replace the damaged part of the integrated circuit, small components should be used, and the wiring should be reasonable to avoid unnecessary parasitic coupling, especially the audio power amplifier integrated circuit and the preamplifier circuit should be properly handled. The ground terminal.
4. It is strictly forbidden to directly test TV, audio, video and other equipment without a power isolation transformer with instruments and equipment with grounded shells. Although the general radio cassette recorder has a power transformer, when you come into contact with more special TV or audio equipment, especially the output power or the nature of the power supply used, you must first find out whether the chassis of the machine is charged, otherwise it is very easy The TV, audio and other equipment that are charged with the bottom plate cause a short circuit of the power supply, which affects the integrated circuit, causing further expansion of the fault.
5. 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.
6. Do not judge that the integrated circuit is damaged easily. Because most integrated circuits are directly coupled, once a circuit is abnormal, it may cause multiple voltage changes, and these changes are not necessarily caused by the damage of the integrated circuit. In addition, in some cases, the measured voltage of each pin is different from the normal When the values match or are close to each other, it does not necessarily mean that the integrated circuit is good. Because some soft faults will not cause changes in DC voltage.