Integrated Circuit Replacement Methods and Techniques

1. Direct Substitution

Direct replacement means directly replacing the original IC with other ICs without any modification, and the replacement does not affect the main performance and indicators of the machine.

The principle of replacement is: the functions, performance indicators, packaging form, pin usage, pin number and spacing of the replaced IC are the same. The same function of the IC not only refers to the same function; it should also be noted that the logical polarity is the same, that is, the output and input level polarity, voltage, and current amplitude must be the same. For example: the ICs in the image, TA7607 and TA7611, the former is a reverse high-amplitude AGC, and the latter is a forward high-amplitude AGC, so they cannot be directly replaced. In addition, ICs that output AFT voltages of different polarities and synchronous pulses of different polarities cannot be directly replaced. Even if they are products of the same company or manufacturer, they should be distinguished. Performance indicators refer to the main electrical parameters of the IC (or main characteristic curves), maximum power dissipation, maximum operating voltage, frequency range, and various signal input and output impedances, which must be similar to the original IC. Low-power substitutes require larger heat sinks. Among them

1. Replacement of IC of the same model

The replacement of ICs of the same model is generally reliable. When installing the integrated circuit , be careful not to make a mistake in the direction, otherwise the integrated circuit may be burned when powered on. Some single-row in-line amplifier ICs have the same model, function, and characteristics, but the direction of the pin arrangement sequence is different. For example, the dual-channel amplifier IC LA4507 has "positive" and "negative" pins, and the starting pin marking (color dot or pit) has different directions; there are ICs without suffixes and ICs with suffix "R", such as M5115P and M5115RP.

2. Replacement of different IC models

⑴ Replacement of ICs with the same prefix letters but different numbers. As long as the pin functions are exactly the same and the internal circuits and electrical parameters are slightly different, they can be directly replaced. For example, the LA1363 and LA1365 ICs are placed in the accompaniment. The latter has a voltage regulator diode added to the ⑤th pin of the IC, and the rest are exactly the same.

⑵ Replacement of ICs with different prefix letters but the same numbers. Generally, the prefix letters indicate the manufacturer and the type of circuit. If the numbers after the prefix letters are the same, most of them can be directly replaced. However, there are a few that have the same numbers but completely different functions. For example, HA1364 is a sound IC, while UPC1364 is a color decoding IC; 4558, the 8-pin is the operational amplifier NJM4558, and the 14-pin is the CD4558 digital circuit; therefore, the two cannot be replaced at all.

⑶ Replacement of ICs with different prefix letters and numbers. Some manufacturers import unpackaged IC chips and then process them into products named after their own factories. Others improve products in order to improve certain parameter indicators. These products are often named with different models or distinguished by model suffixes. For example, AN380 and UPC1380 can be directly replaced; AN5620, TEA5620, DG5620, etc. can be directly replaced.

2. Indirect Substitution

Indirect replacement refers to a method of making an IC that cannot be directly replaced by slightly modifying the peripheral circuit, changing the original pin arrangement, or adding or removing individual components to make it a replaceable IC.

Replacement principle: The IC used for replacement may have different pin functions and appearance from the original IC, but the functions must be the same and the characteristics must be similar; the performance of the original machine should not be affected after replacement.

1. Replacement of ICs with different packages

For IC chips of the same type but with different package shapes, when replacing them, just reshape the pins of the new device according to the shape and arrangement of the pins of the original device. For example, the AFT circuit CA3064 and CA3064E, the former is a round package with radial pins; the latter is a dual in-line plastic package. The internal characteristics of the two are exactly the same, and they can be connected according to the pin function. The dual-in-line IC AN7114, AN7115 and LA4100, LA4102 have basically the same package form, and the pins and heat sinks are exactly 180° apart. The AN5620 dual in-line 16-pin package with heat sink and the TEA5620 dual in-line 18-pin package mentioned above, pins 9 and 10 are located on the right side of the integrated circuit , which is equivalent to the heat sink of AN5620. The other pins of the two are arranged the same. Connect pins 9 and 10 and ground them for use.

2. Replacement of ICs with the same circuit functions but different individual pin functions

When replacing, you can follow the specific parameters and instructions of each model IC. For example, the AGC and video signal output in a TV set has positive and negative polarity differences, and you can replace them by adding an inverter to the output end.

3. Replacement of ICs of the same type but with different pin functions

This replacement requires changes to the peripheral circuit and pin arrangement, and therefore requires certain theoretical knowledge, complete information, and rich practical experience and skills.

4. Some empty feet should not be grounded without permission

Some pins in the internal equivalent circuit and application circuit are not marked. When you encounter empty pins, you should not ground them without authorization. These pins are replacement or spare pins and are sometimes used as internal connections.

5. Replace ICs with discrete components

Sometimes you can use discrete components to replace the damaged part of the IC to restore its function. Before replacing, you should understand the internal function principle of the IC, the normal voltage of each lead pin, the waveform diagram, and the working principle of the circuit composed of peripheral components. At the same time, you should also consider:

⑴ Whether the signal can be taken out from the IC and connected to the input end of the peripheral circuit:

⑵Can the signal processed by the peripheral circuit be connected to the next level inside the integrated circuit for further processing (the signal matching during connection should not affect its main parameters and performance). If the IF amplifier IC is damaged, from the typical application circuit and internal circuit, it is composed of the accompanying audio IF amplifier, frequency discrimination and audio amplifier stage. The signal injection method can be used to find the damaged part. If the audio amplifier part is damaged, it can be replaced with discrete components.

6. Combination substitution

Combination replacement is a method of combining the undamaged circuit parts of multiple ICs of the same model into a complete IC to replace the IC with poor function. It is very suitable when the original IC is not available. However, it is required that the intact circuit inside the IC used must have an interface lead pin.

The key to indirect replacement is to find out the basic electrical parameters, internal equivalent circuits, functions of each pin, and connection relationship between IC and external components of the two ICs to be replaced. Pay attention to the following in actual operation:

⑴The numbering sequence of the integrated circuit pins should not be wrong;

⑵ In order to adapt to the characteristics of the replaced IC, the components of the peripheral circuits connected to it must be changed accordingly;

⑶ Power supply The voltage should match that of the replaced IC. If the voltage of the original circuit is high, try to reduce it; if the voltage is low, see if the replaced IC can work.

⑷After replacement, measure the static working current of IC. If the current is much larger than the normal value, it means that the circuit may be self-excited. At this time, decoupling and adjustment are required. If the gain is different from the original, adjust the feedback resistor value;

⑸ The input and output impedance of the replaced IC should match the original circuit; check its driving capability.

(6) When making changes, make full use of the pin holes and leads on the original circuit board. The external leads should be neat and avoid crossing each other, so as to check and prevent circuit self-excitation, especially high-frequency self-excitation.

(7) Before power is turned on, it is best to connect a DC ammeter in series in the power supply Vcc loop, and observe whether the change of the total current of the integrated circuit is normal by decreasing the resistance of the voltage-dropping resistor from large to small.