9 basic common sense of PCB board inspection-PCBQuick
1. It is strictly prohibited to use the grounded test equipment to touch the live TV, audio, video and other equipment on the base plate to detect the PCB board without isolating transformer
It is forbidden to directly test TV, audio, video and other equipment without power isolating transformer with equipment with grounded enclosure. Although generally the recorder has power transformer, when exposed to a special especially or larger output power of the nature of the power supply do not know much about TV or stereo equipment, first make clear the machine chassis is charged, otherwise extremely easy and floor live TV, audio and other equipment power supply circuit, spread to the integrated circuit, further breakdowns.
2. Pay attention to the insulation performance of electric soldering iron when testing PCB board
It is not allowed to use soldering iron for soldering. To ensure that the soldering iron is not electrified, it is best to ground the shell of the soldering iron. You should be more careful with MOS circuit.
3. Understand the working principle of integrated circuits and related circuits before testing the PCB board
Before checking and repairing an integrated circuit, it is necessary to be familiar with the function of the integrated circuit, internal circuit, main electrical parameters, functions of each pin, normal voltage of the pin, waveform and working principle of the circuit composed of peripheral components. If the above conditions are met, then the analysis and inspection will be much easier.
4. Test PCB board should not cause short circuit between pins
When the voltage is measured or the waveform is tested with the oscilloscope probe, the watch pen or probe should not cause short circuit between the integrated circuit pins due to sliding, and it is best to measure on the peripheral printed circuit directly connected with the pin. Any momentary short circuit can easily damage an integrated circuit, especially when testing flat CMOS integrated circuits.
5, test PCB test instrument internal resistance to be large
Dc voltage measurement IC pin, should choose header Ω resistance is greater than 20 k/V multimeter, or for some pin voltage will have larger error of measurement.
6. Pay attention to heat dissipation of power integrated circuit when detecting PCB board
Power integrated circuit should be good heat dissipation, not allowed to work without a radiator in the state of high power.
7. Test PCB lead shall be reasonable
If it is necessary to add peripheral components to replace the damaged part inside the integrated circuit, small components should be selected, and the wiring should be reasonable to avoid unnecessary parasitic coupling, especially to deal with the grounding terminal between the audio power amplifier integrated circuit and the preamplifier circuit.
8. PCB inspection shall ensure the welding quality
Welding is indeed firm, the accumulation of solder, gas hole is easy to cause virtual welding. The welding time is generally not more than 3 seconds, the power of the soldering iron should be about 25W. The already welded integrated circuit should be carefully examined, it is best to use the ohmmeter to measure whether there is a short circuit between the pins, and confirm that there is no solder adhesion before connecting the power supply.
9, test PCB board do not easily determine the damage of the integrated circuit
Do not easily judge that the integrated circuit is damaged. Since most integrated circuits are directly coupled, once a circuit is abnormal, it may lead to multiple voltage changes, which may not be caused by the damage of the integrated circuit. In addition, under some circumstances, when the measured voltage of each pin is consistent with or close to the normal value, it may not indicate that the integrated circuit is good. Because some soft faults will not cause dc voltage changes.