Four major performance tests of digital integrated circuits

    First, the voltage method to judge whether the digital integrated circuit is good or bad
    1. If the power supply voltage of the digital integrated circuit is normal and the welding is good, but the measured voltage value of the power pin is too low, it can be judged that the digital integrated circuit under test is damaged.
    2. If the measured voltage value of the power supply voltage pin of the digital integrated circuit is normal, but the voltage values of other pins are mostly abnormal, it means that the ground pin is weakly welded, and the integrated circuit is mostly normal.
    3. If the measured voltage value of individual or a few pins of the digital integrated circuit deviates greatly from the normal value, you should first check whether the original peripheral component circuit corresponding to this pin is faulty, such as short circuit of resistance, open circuit, Capacitor leakage or breakdown, etc. If there is no fault in the circuit of peripheral components, it means that the digital integrated circuit under test is damaged.
    4. If the measured voltage values of most pins of the digital integrated circuit deviate from the normal value by a large amount, and the voltage of the power supply is normal, and the power supply and ground pins are not soldered, it can be determined that the digital integrated circuit is damaged.
    Second, TTL circuit quality performance testing
    Carefully observe the model of the TTL integrated circuit, look up the relevant data sheet, find out the grounding terminal of the integrated circuit, and find out its internal circuit diagram or wiring diagram.
    Turn the selection switch of the multimeter to the R×1K position, the black test lead is connected to the ground terminal of the integrated circuit under test, and the red test lead is used to test the DC resistance value of each input terminal and output terminal to the ground in turn. Under normal circumstances, the resistance value of each pin of the integrated circuit to ground should be 3~10kΩ. If the resistance value of a pin to ground is less than 1 kΩ or greater than 12 kΩ, the integrated circuit has been damaged.
    Ground the red pen of the multimeter, and test the input and output terminals of the integrated circuit in sequence with the black test pen. Under normal circumstances, the reverse resistance value of each end to ground should be greater than 40 kΩ. The resistance value of each pin of the damaged integrated circuit to ground is lower than 1 kΩ. For the positive and negative pins of the power supply of a normal TTLT circuit, the forward and reverse resistance values are smaller than those of other pins to ground, not exceeding 10 kΩ. A value of zero or infinity indicates that the power pin of this IC is broken.
    3. Voltage method to distinguish TTL circuit and CMOS circuit
    According to their models, such as CC4000, CD4006 and MC14021 are all CMOS circuits, while CT3020 and 74 series are all TTL circuits.
    According to its power supply voltage, if it can work normally under the voltage of 3~4.5V or 5.5~18V without knowing the model of the digital integrated circuit, it can be sure that it is a CMOS circuit. You can also use a multimeter to test the output level of the integrated circuit. When the power supply voltage is 5V, connect the input terminal of the circuit to high level and low level, and then use a multimeter to test the output terminal. If the difference between the tested high and low levels is close to 5V , it is a CMOS integrated circuit; if it is close to 3.5V, it is a TTL integrated circuit.
    Distinguish according to the voltage value of its output level: take a simple gate circuit as an example, the power supply voltage is 5V, put the multimeter in the DC voltage 10V range, connect the input terminals of the integrated circuit to high and low levels in turn, and measure the The voltage value corresponding to the high and low levels of the output terminal. If the difference between them is close to 5V, it is a CMOS circuit; if the difference between them is close to 3.5V, it is a TTL circuit.
    Fourth, distinguish between CMOS circuits and high-speed CMOS circuits
    Since the power supply voltage of the CMOS circuit is 3~18V, and the power supply voltage of the high-speed CMOS circuit is 2~6V, when a voltage of 2~2.5V is applied to the integrated circuit, if the integrated circuit works normally, it means that the integrated circuit is a high-speed CMOS circuit. circuit, otherwise, this integrated circuit is a CMOS circuit.