Testing method for integrated circuits using only a multimeter as a testing tool
Although integrated circuit replacement is easy, disassembly is troublesome after all. Therefore, before disassembly, you should accurately determine whether the integrated circuit is indeed damaged and the extent of the damage to avoid blind disassembly. This article introduces the methods and precautions for out-of-circuit and on-circuit testing of integrated circuits using only a multimeter as a testing tool. The four on-road detection methods described in this article (measurement of DC resistance, voltage, AC voltage and total current) are practical and commonly used detection methods in amateur maintenance. Here, I also hope that everyone can provide other practical (integrated circuits and components) identification and testing experience.
(1) Off-road detection
This method is performed when the IC is not soldered into the circuit. Generally, a multimeter can be used to measure the forward and reverse resistance values between each pin corresponding to the ground pin, and compare it with the intact IC.
(2) On-road detection
This is a detection method that uses a multimeter to detect the DC resistance of each pin of the IC (the IC is in the circuit), the AC and DC voltage to ground, and the total operating current. This method overcomes the limitations of the substitution test method, which requires a replaceable IC and the trouble of disassembling the IC. It is the most commonly used and practical method for detecting ICs.
1． On-circuit DC resistance detection method
This is a method of using the ohm block of a multimeter to measure the forward and reverse DC resistance values of each pin of the IC and peripheral components directly on the circuit board, and comparing it with the normal data to find and determine the fault. Pay attention to the following three points when measuring:
(1) Disconnect the power supply before measuring to avoid damaging the meter and components during testing.
(2) The internal voltage of the multimeter's electrical barrier must not be greater than 6V. It is best to use the R×100 or R×1k range for the measurement range.
(3) When measuring IC pin parameters, pay attention to the measurement conditions, such as the model under test, the position of the sliding arm of the potentiometer related to the IC, etc., and also consider the quality of the peripheral circuit components.
2． DC operating voltage measurement method
This is a method of measuring the DC power supply voltage and the working voltage of peripheral components with a multimeter DC voltage block when power is on; detecting the DC voltage value of each pin of the IC to ground, and comparing it with the normal value, thereby compressing the fault range. Find the damaged component. Pay attention to the following eight points when measuring:
(1) The multimeter must have a large enough internal resistance, at least 10 times greater than the resistance of the circuit being measured, to avoid 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 test leads or probes. Any instantaneous short circuit can easily damage the IC. The following method can be used to prevent the test pen from sliding: take a piece of bicycle valve core and put it on the test pen tip, and extend the test pen tip by about 0.5mm. This can not only make the test pen tip well in contact with the tested point, but also effectively prevent slipping. , there will be no short circuit even if it hits adjacent points.
(4) When the measured voltage of a certain pin does not match the normal value, the quality of the IC should be judged by analyzing whether the pin voltage has any important impact on the normal operation of the IC and the corresponding changes in the voltage of other pins.
(5) IC pin voltage will be affected by peripheral components. When peripheral components leak, short circuit, open circuit or change value, or the peripheral circuit is connected to a potentiometer with variable resistance, the pin voltage will change due to different positions of the potentiometer's sliding arm.
(6) If the voltage of each pin of the IC is normal, the IC is generally considered normal; if the voltage of some pins of the IC is abnormal, you should start from the point that deviates the most from the normal value and 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 televisions, the voltages of each pin of the IC are different when there is a signal or not. If it is found that the pin voltage should not change but changes greatly, and the pin voltage that should change with the signal size and the position of the adjustable component does not change, it can be determined that the IC is damaged.
(8) For devices with multiple working modes, such as video recorders, the voltages of each pin of the IC are also different in different working modes.
