PCB circuit board proofing a few tips of common sense

1, the detection of PCB board should pay attention to the insulation performance of electric soldering iron.

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

2. Before testing PCB board, we should understand the working principle of integrated circuit and its related circuits.

Before checking and repairing integrated circuit, we should be familiar with the function, internal circuit, main electrical parameters, the role of each pin and the normal voltage, waveform of the pin and the working principle of the circuit composed of peripheral components. If these conditions are in place, analysis and inspection are much easier.

3. It is strictly prohibited to test PCB circuit boards with grounded test equipment to contact TV, audio, video and other equipment with live on the bottom plate without isolating transformer.

It is strictly prohibited to directly test TV, audio, video and other equipment without power isolation transformer with the instrument whose shell has been grounded. Although the general radio recorder has a power transformer, when exposed to the more special especially large output power or the nature of the power supply is not very familiar with the television or audio equipment, first of all to make clear whether the chassis of the machine is live, otherwise it is easy to and floor live TV, audio and other equipment caused by short circuit, ripple integrated circuit, resulting in further expansion of the fault.

4, test printed circuit board test instrument to large internal resistance

When measuring the DC voltage of integrated circuit pins, use a multimeter with an internal resistance greater than 20 kω /V. Otherwise, there will be a large measurement error for some pins.

5, the detection of PCB board should pay attention to the heat dissipation of power integrated circuit

The power integrated circuit should have good heat dissipation, and it is not allowed to work in the state of high power without a radiator.

6, testing PCB board to ensure the quality of welding

Welding is really solid, the accumulation of solder, porosity is easy to cause virtual welding. Welding time is generally not more than 3 seconds, the power of the iron should be about 25W internal heat. The soldered integrated circuit should be carefully checked. It is best to use an ohmmeter to measure whether there is short circuit between the pins and confirm that there is no solder adhesion before switching on the power supply.

7, the detection of PCB board lead should be reasonable

If it is necessary to add peripheral components to replace the damaged part of the integrated circuit, small components should be selected, and the wiring should be reasonable to avoid unnecessary parasitic coupling, especially to deal with the audio power amplifier integrated circuit and the ground terminal between the circuit.

8, detection circuit board do not easily determine the damage of integrated circuit

Don't jump to the conclusion that the IC is damaged. Because the vast majority of integrated circuits are direct coupling, once a circuit is abnormal, it may lead to multiple voltage changes, and these changes are not necessarily caused by the damage of integrated circuits, in addition, in some cases when the pin voltage is measured in accordance with or close to the normal value, it may not be able to show that the integrated circuit is good. Because some soft faults do not cause a change in DC voltage.

9, test PCB board do not cause short circuit between pins

Voltage measurement or oscilloscope probe test waveform, the pen or probe should not be caused by sliding short circuit between the pins of the integrated circuit, it is best to measure in the peripheral printed circuit directly connected with the pins. Any momentary short circuit can easily damage the IC, and extra care should be taken when testing CMOS integrated circuits in flat packages.