9 Points for Testing of PCB Board

1. Strictly prohibited in the absence of isolation transformer, with grounded test equipment to contact the bottom plate charged TV, audio, video and other equipment to test the PCB board.

It is strictly prohibited to use the shell has been grounded instruments and equipment directly test the TV, audio, video and other equipment without power isolation transformer. Although the general recorder has a power transformer, when contacting the more special, especially the output power or the nature of the power supply used is not well understood when the TV or audio equipment, the first thing to find out whether the machine chassis charged, otherwise it is very easy and the chassis charged TV, audio and other equipment caused by power short circuit, and integrated circuits, resulting in further expansion of the fault.

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2, Pay attention to the insulation properties of the soldering iron

Do not allow the use of soldering iron with electricity, to confirm that the iron is not charged, it is best to ground the shell of the iron, the MOS circuit should be more careful, can use 6 to 8V low-voltage soldering iron on the safer.

3, Understand the working principle of the integrated circuit and its related circuits before testing the PCB board.

Inspection and repair of integrated circuits before the first to be familiar with the function of the integrated circuit used, the internal circuit, the main electrical parameters, the role of the pins and the normal voltage of the pins, waveforms and peripheral components to form the working principle of the circuit. If you have the above conditions, then the analysis and inspection will be much easier.

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4, Do not cause a short circuit between the pins

?Voltage measurement or waveform testing with an oscilloscope probe, the meter pen or probe do not cause a short circuit between the pins of the integrated circuit due to sliding, it is best to measure on the peripheral printed circuit directly connected to the pins. Any instantaneous short circuit can easily damage the integrated circuit, in the test flat type package CMOS integrated circuit should be doubly careful.

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5,Internal resistance of test meters to be large

?Measurement of integrated circuit pins DC voltage, you should use the meter head resistance greater than 20KΩ / V multimeter, otherwise the voltage on some pins will have a large measurement error.

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6, Pay attention to the power integrated circuit heat dissipation

?Power integrated circuit should be good heat dissipation, not allowed to work without a heat sink and in a high power state.

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7, Be reasonable to the detection of PCB board

If you need to add peripheral components instead of IC internal damaged part, should choose small components, and wiring should be reasonable to avoid unnecessary parasitic coupling, especially to deal with the audio amplifier IC and pre-amplifier circuit between the ground terminal.

?8, Ensure the quality of welding

Welding does weld firmly, the buildup of solder, air holes are likely to cause false welding. Welding time is generally no more than 3 seconds, the power of the soldering iron application internal heating type 25W or so. Have been welded IC to look carefully, it is best to use the ohmmeter to measure whether there is a short circuit between the pins, to confirm that there is no solder adhesion phenomenon before turning on the power.

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9, Do not easily conclude that the integrated circuit damage

?Do not easily judge the integrated circuit has been damaged. Because the vast majority of integrated circuits for direct coupling, once a circuit is not normal, may lead to multiple voltage changes, and these changes are not necessarily caused by damage to the integrated circuit, in addition, in some cases, the measured voltage of the pins and the normal value of the match or close, it does not necessarily mean that the integrated circuit is good. Because some soft faults do not cause changes in DC voltage.

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