PCB Tech - Several common sense of PCB proofing

How many 9 tips do you know about PCB circuit board proofing?

1. Pay attention to the insulation function of the electric soldering iron when detecting the PCB board

It is not allowed to use a soldering iron for soldering with power. It is necessary to admit that the soldering iron is not charged. Ground the shell of the soldering iron. Be more careful with the MOS circuit. It is safer to use a low-voltage circuit iron of 6~8V.

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

Before inspecting and repairing the integrated circuit, we must first understand 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, the analysis and inspection will be much simpler.

3. It is strictly forbidden to use grounded test equipment to touch the live TV, audio, video and other equipment of the bottom plate to test the PCB board without a barrier transformer.

It is strictly forbidden to directly test TV, audio, video and other equipment without a power supply barrier 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 selected power supply, you must first clarify whether the chassis of the machine is charged, otherwise it will be very easy to interact with The TVs, audios and other equipment with live baseboards form power short circuits, which involve integrated circuits, which cause further expansion of the faults. Circuit board manufacturers

4. The internal resistance of the PCB board test instrument should be large

When measuring the DC voltage of the pins of an integrated circuit, a multimeter with an internal resistance greater than 20KΩ/V in the header should be selected, otherwise there will be larger measurement errors for some pin voltages.

5. Pay attention to the heat dissipation of the power integrated circuit when testing the PCB board

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

6. Check the PCB board to ensure the welding quality

The welding is indeed firm, and the accumulation of solder and pores simply form a virtual weld. The soldering time generally does not exceed 3 seconds, and the power of the soldering iron should be about 25W using internal heating. The integrated circuit that has been soldered should be checked carefully, use an ohmmeter to measure whether there is a short circuit between the pins, and then turn on the power after admitting that there is no solder adhesion.

7. The lead wire of the PCB board should be tested reasonably

If it is necessary 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 grounding between the audio power amplifier integrated circuit and the preamplifier circuit end.

8. Do not easily determine the damage of the integrated circuit when testing the PCB board

Do not easily distinguish that the integrated circuit is damaged. Since most integrated circuits are directly coupled, once a certain circuit is abnormal, it may cause multiple voltage changes, and these changes are differently caused by the damage of the integrated circuit. In other cases, the voltage of each pin is measured. When it is in line with or close to the normal value, it can be said that the integrated circuit is good. Due to some soft problems, the DC voltage will not change.

9. Do not form a short circuit between pins when testing the PCB board

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 leads or probes, and measure on the peripheral printed circuit directly connected to the pins. Any momentary short-circuit will simply damage the integrated circuit, and you must be more careful when testing flat-package CMOS integrated circuits.