Matters needing attention when testing IC with a multimeter
This is a way to measure the DC supply voltage and the working voltage of peripheral components with a DC voltage block under the condition of power on; detect the DC voltage value of each pin of the IC to the ground, and compare it with the normal value, and then compress the fault range and find out damaged components. Pay attention to the following eight points when measuring:
1. The internal resistance of the multimeter must be large enough, at least 10 times greater than the resistance of the circuit under test, so as not to cause large measurement errors.
2. Usually, turn each potentiometer to the middle position. If it is a TV, the signal source should use a standard color bar signal generator.
3. Anti-slip measures should be taken for the test leads or probes. Any momentary short circuit can easily damage the IC. The following methods can be adopted to prevent the test pen from sliding: take a bicycle valve core and put it on the test pen tip, and grow the test pen tip by about 0.5mm, which can not only make the test pen tip in good contact with the tested point, but also effectively prevent slipping. It will not be short-circuited even if it hits a neighboring point.
4. When the measured voltage of a certain pin does not match 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 in the voltage of other pins, so as to judge whether the IC is good or bad.
5. IC pin voltage will be affected by peripherals. When leakage, short circuit, open circuit or value change occurs in peripheral components, or the peripheral circuit is connected to a potentiometer with variable resistance, the position of the sliding arm of the potentiometer is different, which will cause the pin voltage to change.
6. If the voltage of each pin of the IC is normal, it is generally considered that the IC is normal; if the voltage of some pins of the IC is abnormal, you should start from the point where the deviation from the normal value is the largest, and check whether there is any fault in the peripheral components. 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 the IC is different when there is a signal or not. If it is found that the pin voltage should not change but changes greatly, and the one that should change with the signal size and the different positions of the adjustable element does not change, it can be determined that the IC is damaged.
8. For devices with multiple working modes, such as video recorders, the voltage of each pin of the IC is also different under different working modes.
