How can a multimeter quickly judge whether the IC chip of an integrated circuit is normal or damaged?

Date：2021-12-08 14:19:31Views：3389

The multimeter can be used to measure not only the resistance of the measured object, but also the AC and DC voltage. Even some multimeters can measure the main parameters of transistors and the capacitance of capacitors. Fully mastering the use of multimeter is one of the most basic skills of electronic technology. How can a multimeter quickly judge whether the IC chip of an integrated circuit is normal or damaged?

DC working voltage measurement method

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 shall have a large enough internal resistance, which shall be at least 10 times greater than the resistance of the circuit to be measured, 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 taken to prevent the probe from sliding: take a section of bicycle valve core to cover 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 should 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.

In circuit DC resistance detection method

This is a method to find and determine the fault by directly measuring the forward and reverse DC resistance of IC pins and peripheral components on the circuit board with the ohm gear of the multimeter and comparing it with the normal data. Pay attention to the following three points during measurement:

(1) Disconnect the power supply before measurement to avoid damaging the meter and components during test.

(2) The internal voltage of the resistance gear of the multimeter shall not be greater than 6V, and the range is preferably R × 100 or R × 1K gear.

(3) When measuring IC pin parameters, pay attention to the measurement conditions, such as the tested model, the sliding arm position of potentiometer related to IC, and also consider the quality of peripheral circuit components.

Total current measurement method

This method is a method to judge the quality of IC by detecting the total current of IC power 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.

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 jack, connect a 0.1 ~ 0.5 Multimeter in series with the positive probe μ F. isolation capacitance. 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.

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