How does the IC chip detect normal? Share dry goods and avoid detours

Date：2021-11-30 11:17:04Views：1572

Brief introduction of IC chip IC chip (integrated circuit) is an integrated circuit formed by a large number of microelectronic components (transistors, resistors, capacitors, etc.) on a plastic base to make a chip. Now almost all the chips we see can be called IC chips. Integrated circuit is a kind of micro electronic device or component.

General knowledge of IC chip detection

1. Understand the working principle of integrated circuits and related circuits before testingBefore 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. If the above conditions are met, the analysis and inspection will be much easier.

2. The test shall not cause short circuit between pinsWhen measuring voltage or testing waveform with oscilloscope probe, the lead or probe shall not cause short circuit between integrated circuit pins due to sliding, and it is best to measure on the peripheral printed circuit directly connected with the pins. Any instantaneous short circuit is easy to damage the integrated circuit. Be more careful 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 transformerIt 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 ironIt 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. To ensure the welding quality, it is necessary to weld firmly during welding, and the accumulation of solder and pores 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 easilyDo 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 largeWhen 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 circuitsThe 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 reasonableIf 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.

Method for detecting normal operation of IC chip

1. Off road detection

This method is carried out when the IC is not welded into the circuit. Generally, the forward and reverse resistance values between each pin corresponding to the grounding pin can be measured with a multimeter, and compared with a intact IC.

2. On road detection

This is a method to detect the DC resistance of IC pins in the circuit (IC in the circuit), AC / DC voltage to ground and total working current through a multimeter. This method overcomes the limitation of substituting IC and the trouble of disassembling IC. It is the most common and practical method to detect IC.

3. DC working voltage measurement

This is a method to measure the DC power supply voltage and the working voltage of peripheral components with the DC voltage gear of multimeter when powered on; Detect the DC voltage value of each IC pin to the ground and compare it with the normal value, so as to compress the fault range and find out the damaged components. Pay attention to the following eight points during measurement:

(1) The multimeter should have enough internal resistance, which should be at least 10 times greater than the resistance of the measured circuit, so as not to cause large measurement error.

(2) Usually turn each potentiometer to the middle position. If it is a TV, the signal source should adopt a standard color bar signal generator.

(3) Anti skid measures shall be taken for the probe or probe. IC is easily damaged due to any instantaneous short circuit. The following methods can be adopted to prevent the probe from sliding: take a section of bicycle valve core and cover it on the probe tip, and grow the probe tip by about 0.5mm, which can not only make the probe tip in good contact with the tested point, but also effectively prevent slipping, and there will be no short circuit even if it touches the adjacent point.

(4) When the measured voltage of a pin is inconsistent with the normal value, it shall be analyzed according to whether the pin voltage has an important impact on the normal operation of the IC and the corresponding changes of other pin voltages, so as to judge the quality of the IC.

(5) IC pin voltage will be affected by peripheral components. In case of leakage, short circuit, open circuit or variable value of peripheral components, or a potentiometer with variable resistance is connected to the peripheral circuit, the pin voltage will change due to the different position of the sliding arm of the potentiometer.

(6) If the voltage of each IC pin is normal, the IC is generally considered normal; If the pin voltage of IC part is abnormal, start from the maximum deviation from the normal value to check whether the peripheral components are faulty. If there is no fault, the IC is likely to be damaged.

(7) For dynamic receiving devices, such as TV sets, the voltage of each pin of IC is different when there is no signal. If it is found that the pin voltage should not change, but does not change with the signal size and different positions of adjustable components, it can be determined that the IC is damaged.

(8) For devices with multiple working modes, such as video recorders, the voltage of each IC pin is also different under different working modes.

4. AC working voltage measurement method

In order to master the change of IC AC signal, a multimeter with DB jack can be used to approximately measure the AC working voltage of IC. During detection, the multimeter is placed in the AC voltage gear, and the positive probe is inserted into the DB jack; For a multimeter without DB socket, a 0.1 ~ 0.5 multimeter shall be connected in series with the positive probe μ F) DC isolation capacitor. This method is suitable for IC with low working frequency, such as video amplification stage of TV, field scanning circuit, etc. Because the natural frequencies and waveforms of these circuits are different, the measured data are approximate and can only be used for reference.

5. Total current measurement method

This method is a method to judge the quality of IC by detecting the total current of IC power supply incoming line. Because most of the IC is directly coupled, when the IC is damaged (such as a PN junction breakdown or open circuit), it will cause the later stage saturation and cut-off, and change the total current. Therefore, the quality of IC can be judged by measuring the total current. The total current can also be calculated by measuring the voltage drop of the resistance in the power path and using Ohm's law.

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