1. Before testing, understand the working principle of integrated circuits and related circuits

Before checking and repairing an 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, and the working principle of the circuit composed of the normal voltage, waveform and peripheral components of the pins.

2. Test to avoid short circuit between pins

When measuring voltage or testing waveforms with an oscilloscope probe, avoid short circuits between pins, and only measure on peripheral printed circuits that are directly connected to the pins. Any momentary short circuit can easily damage the integrated circuit, especially when testing flat-pack CMOS integrated circuits.

3. It is strictly forbidden to use the grounded test equipment to touch the live TV, audio, video and other equipment on the bottom without an isolation transformer.

It is strictly forbidden to directly test TV, audio, video and other equipment without power isolation transformers with equipment with grounded shells. Although the general tape recorder has a power transformer, when you come into contact with a more special TV or audio equipment with a large output power or a lack of understanding of the power supply used, you must first find out whether the chassis of the machine is charged, otherwise it is very easy to The TV, audio and other equipment that are charged with the bottom plate cause a short circuit in the power supply, which affects the integrated circuit and further expands the failure.

4. Pay attention to the insulation properties of the soldering iron

It is not allowed to use a soldering iron to solder with electricity. Make sure that the soldering iron is not electrified. Make sure that the shell of the soldering iron is grounded. Be careful with MOS circuits. It is safer to use a low-voltage electric soldering iron of 6~8V.

5. To ensure the welding quality

When welding, it is indeed welded firmly, and the accumulation of solder and pores are easy to cause virtual welding. The welding time is generally not more than 3 seconds, and the power of the soldering iron is about 25W for the internal heat type. The soldered integrated circuits should be carefully checked, first 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.

6. Do not easily conclude that the integrated circuit is damaged

Do not easily judge that the integrated circuit is damaged. Because most 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 the damage of the integrated circuit. When the values are consistent or close, it does not necessarily mean that the integrated circuit is good. Because some soft faults do not cause changes in DC voltage.

7. The internal resistance of the test instrument should be large

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

8. Pay attention to the heat dissipation of power integrated circuits

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

9, the 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 the grounding between the audio power amplifier integrated circuit and the preamplifier circuit should be handled well. end.