1. It is strictly forbidden to use grounded test equipment to touch the live TV, audio, video and other equipment on the bottom board to test the PCB board without an isolation transformer.
It is strictly forbidden to directly test TV, audio, video and other equipment without power isolation transformer with the equipment whose casing has been grounded. Although general tape recorders have power transformers, when you come into contact with special TVs or audio equipment, especially those with high output power or do not know the nature of the power supply used, you must first find out whether the chassis of the radio is live, otherwise it will be very easy. The TV, audio and other equipment charged with the bottom plate will cause a short circuit of the power supply, which will affect the integrated circuit and cause further expansion of the fault.
2. Pay attention to the insulation performance of the electric soldering iron when testing the PCB board
It is not allowed to use a soldering iron to weld with electricity. Make sure that the soldering iron is not charged. It is best to 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. Before detecting the PCB board, it is necessary to understand the working principle of the integrated circuit and its related circuits
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 function of each pin, 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 test the PCB board to cause a short circuit between pins
When measuring voltage or testing waveforms with oscilloscope probes, the test leads or probes should not cause short circuits between the pins of the integrated circuit due to sliding. It is best to measure on the peripheral printed circuit that is directly connected to the pins. Any momentary short circuit can easily damage the integrated circuit, and extra care should be taken when testing flat packaged CMOS integrated circuits.
5. The internal resistance of the PCB board test instrument should be large
When measuring the DC voltage of the pins of the integrated electric arm of the star, a multimeter with an internal resistance of the meter head greater than 2OKQ/V should be selecte, otherwise there will be a large measurement error for the voltage of some pins.
6. Pay attention to the heat dissipation of power integrated circuits when detecting PCB boards
The power integrated circuit should have good heat dissipation, and it is not allowed to work in a high-power state without a radiator.
7. The detection of PCB board lead wires should be reasonable
If it is necessary to add external components to replace the damaged parts inside the integrated circuit, small components should be selecte, 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. turbulence.
8. Inspection of PCB boards should ensure the welding quality
Be sure to weld firmly during welding, and the accumulation of solder and pores are likely to cause false welding. The welding time generally does not exceed 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, and then turn on the power after confirming that there is no solder adhesion.
9. Do not easily determine the damage of the integrated circuit when detecting the PCB board
Do not easily judge that the integrated circuit is damaged. Because the vast majority of integrated circuits are directly coupled, once a certain circuit is abnormal, it may cause multiple voltage changes, and these changes are not necessarily caused by damage to the integrated circuit. When the normal value is consistent or close, it does not necessarily mean that the integrated circuit is good. Because some soft faults will not cause changes in DC voltage.
