Replacement methods and principles of integrated circuits

In the development and maintenance of electronic products. After considering the cost, or confirming the damage of an integrated circuit, it is usually necessary to replace it with an integrated block that conforms to the specifications and model of the original device. It is not easy to find a replacement with the original device specifications and models. Therefore, how to find an integrated circuit device that can replace the original product becomes the key to maintenance. Learn about common types of faults in integrated circuits. Master the principles, methods, and precautions for integrated circuit replacement. It can make repair or replace the integrated circuit more efficient. '

First, the type of integrated circuit failure

We can think of each integrated circuit (referred to as "component") as a black box with a power supply, input, output, and certain functions, without having to delve into the internal circuit structure, as long as its power supply terminal is known and its input is known. If the logical relationship between the outputs is correct, it is considered normal, otherwise it indicates that the component is faulty. Component failures can often be divided into two types: component internal circuit faults and component external circuit faults.

1. Component internal circuit failure

(1) The input and output feet are desoldered and opened.

(2) The input and output pins are shorted to the Ucc power supply or ground.

(3) Short circuit between the Ucc power supply and the two leads other than the ground.

(4) The internal logic function of the component is invalid.

2. Component external circuit failure

(1) Short circuit between Ucc power supply and ground and external circuit nodes.

(2) Short circuit between the two nodes except the Ucc power supply and the ground.

(3) The signal is open.

(4) External component failures such as inductance, capacitance and resistance.

3. Component static parameters and static function failure

In summary, the fault type of the component is nothing more than open circuit, short circuit and functional failure. A large number of practices have proved that the dynamic parameters of the component (delay time, rising edge time, falling edge time) have fewer failures, while static parameters and static functions fail more.

Static parameters and static functions are parameters and functions tested under DC voltage and low frequency signals. There are generally 8 types of malfunctions.

(1) The function current of the component is too large, the component is hot, and the component function is invalid.

(2) The input current of the component is too large, which makes the front load increase, and pulls the signal or level of the previous stage.

(3) The cross leakage current of several inputs is too large, causing the logic function to fail.

(4) There is an open or short circuit in the input and output pins, causing the function to fail.

(5) The frequency characteristics of the component deteriorate. When the operating frequency increases, the amplitude of the output level decreases (for example, the component with the working power supply voltage of 5v is reduced to 3V), causing the function to fail.

(6) The load characteristics of the internal output tube of the component deteriorate, and the low level rises, which is greater than 0.8v (such as between 1v and 2v), which causes the logic to be disordered.

(7) The output current of the internal drive tube of the module is too small. Can not drive the next level of load. Make logic error.

(8) The high and low levels do not meet the requirements. For example, the low level is greater than 0.6V and the high level is less than 2.8V. Such levels are generally referred to as dangerous levels or unreliable levels. Components with such output levels should be rejected. It should be noted that when the output of the open collector component of the collector does not have a matching resistor, the fault level is also generated, but this is not a component failure. It should not be rejected.

The above are the types of faults in digital integrated circuits. For other integrated circuits (such as analog line integrated circuits) can be used as a reference.

Second, the principle of replacement

1. The outline specifications and lead arrangement order should be the same as possible. Use the same type of integrated circuit or other models that can be directly replaced. This can not change the design or the lead of the original circuit. It is simple and easy to meet the design requirements or restore the original machine. Performance indicators. There are a few integrated circuits, although their models are the same, but also consider their form factor.

2. The structure and process type of the circuit should be the same as TTL replacement TTL, CMOS replacement CMOS. ECL replacement ECL, etc.

3. The functional characteristics of the circuit should be the same to ensure that the replacement integrated circuit is good, otherwise it is more difficult to judge the troubleshooting.

4. Some of the main parameters of the circuit should be the same or similar, such as the power supply voltage, operating frequency, and so on.

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