1. Understand the working principle of
integrated circuits and related circuits before testing
Before checking and repairing the integrated circuit, first be familiar with the function, internal circuit, main electrical parameters, the function of each pin, the normal voltage of the pin, the waveform and the working principle of the circuit composed of peripheral components.
2. Test to avoid short circuit between pins
When measuring voltage or testing waveform with oscilloscope probe, avoid short circuit between pins, and it is best to measure on the peripheral printed circuit directly connected with pins. Any instantaneous short circuit is easy to damage the integrated circuit, especially when testing CMOS integrated circuits in flat package.
3. It is strictly prohibited to use grounded test equipment to contact live TV, audio, video and other equipment on the base plate without isolation transformer
It is forbidden to directly test TV, audio, video and other equipment without power isolation transformer with instruments and equipment with grounded shell. Although general tape recorders have power transformers, when contacting special TV or audio equipment with large output power or little understanding of the nature of the power supply used, first make sure whether the chassis of the recorder is charged, otherwise it is very easy to cause power short circuit with TV, audio and other equipment charged on the bottom plate, affect the integrated circuit, and further expand the fault.
4. Pay attention to the insulation performance of electric soldering iron
It is not allowed to use soldering iron for welding with electricity. To confirm that the soldering iron is not charged, it is best to ground the shell of the soldering iron. Be more careful with MOS circuit. It is safer to use low-voltage soldering iron of 6 ~ 8V.
5. Welding quality shall be guaranteed
During welding, it is indeed firmly welded, and the accumulation of solder and air holes are easy to cause false welding. Generally, the welding time shall not exceed 3 seconds, and the power of the soldering iron shall be about 25W. Carefully check the welded integrated circuit. It is best to use an ohmmeter to measure whether there is a short circuit between each pin, confirm that there is no solder adhesion, and then turn on the power supply.
6. Don't judge the damage of
integrated circuit easily
Do not easily judge that the integrated circuit is damaged. Because the vast majority of integrated circuits are directly coupled, once a circuit is abnormal, it may lead to multiple voltage changes, and these changes are not necessarily caused by the damage of the integrated circuit. In addition, in some cases, when the measured voltage of each pin is consistent or close to the normal value, it does not necessarily mean that the integrated circuit is good. Because some soft faults will not cause changes in DC voltage.
7. The internal resistance of the test instrument shall be large(
integrated circuit)
When measuring the DC voltage of integrated circuit pins, a multimeter with an internal resistance greater than 20K Ω / V should be selected, otherwise there will be large measurement error for some pin voltages.
8. Pay attention to the heat dissipation of power
integrated circuits
The power integrated circuit shall have good heat dissipation, and it is not allowed to work at high power without radiator.
9. Lead wires should be reasonable(integrated circuit)
If it is necessary to add peripheral components to replace the damaged parts inside the integrated circuit, small components shall be selected, and the wiring shall be reasonable to avoid unnecessary parasitic coupling, especially the grounding terminal between the audio power amplifier integrated circuit and the preamplifier circuit.
