PCB Technical - PCB technology on the pin number of integrated circuits

Indirect replacement refers to the indirect replacement of the IC slightly modifying the peripheral PCB circuit, changing the original pin arrangement or adding or reducing individual components, etc., making it an alternative IC method.

Replacement principle: The replacement IC can be different from the original IC pin function, the shape is different, but the function should be the same, the characteristics should be similar, and the performance of the original machine should not be affected after the replacement.

1. Different packaged ICs replace the same type of IC chips, but the package shape is different. When replacing, as long as the pins of the new device are reshaped according to the shape and arrangement of the original device pins. For example, the AFTPCB circuit CA3064 and CA3064E, the former is a circular package, radial pins: the latter is a double-row in-line plastic package, the internal characteristics of the two are exactly the same, and can be connected according to the PIN function. The dual-row ICAN7114, AN7115 and LA4100, LA4102 package are basically the same, and the pins and the heat sink are completely separated by 180 degrees.

As mentioned earlier, AN5620 adopts a heat sink dual-row 16-pin package, TEA5620 dual-row 18-pin package, 9 and 10 pins are located on the right side of the integrated PCB circuit, which is equivalent to the heat sink of AN5620, and the other pin is arranged. Use 9,10 feet connected to the ground.

2. The PCB circuit has the same function but the functions of each pin are different. The LC replacement can be replaced according to the specific parameters and instructions of each IC.

For example, for the AGC in the TV, the video signal output has a positive and negative difference, as long as the output end can be replaced after the inverter device.

3. The pin function of the same type of plastic but different IC replacement

This kind of substitution needs to change the peripheral PCB circuit and pin arrangement, so certain theoretical knowledge, complete data and rich practical experience and skills are required.

4. Some empty feet should not be grounded without authorization

The pins derived from the internal equivalent PCB circuit and the application part of the PCB circuit are not marked. If they encounter empty pins, they should not be grounded without authorization. These pins are used for replacement or spare pins, sometimes as internal connections.

5. Combination replacement Combination replacement is the method of using multiple ICS of the same model in the undamaged PCB circuit part to reassemble into a complete IC to replace the dysfunctional IC. It is very suitable for situations where the original IC cannot be purchased.

However, the use of ICs within the integrity of the PCB circuit must have a pin-out interface. The key to indirect replacement is to find out the basic electrical parameters of the two alternative ICSs, the internal equivalent PCB circuit, the function of each pin, and the information about the connection relationship between the IC components.

Pay attention to the actual operation.

(1) The pin number sequence of the integrated PCB circuit should not be connected wrongly; pay attention to the height distribution of the components on the PCB and the shape and size of the PCB

(2) In order to adapt to the characteristics of the replacement IC, the components of the peripheral PCB circuit connected to it should be changed accordingly;

(3) The power supply voltage should be in line with the replacement of work C. If the original PCB circuit power supply voltage is high, try to lower the voltage and lower the voltage to see if the replacement IC can work normally; (4) Measure the quiescent operating current of the IC after replacement, such as The current is much larger than the normal value, indicating that the PCB circuit may be self-excited, so decoupling and adjustment are required.

If the gain is different from the original gain, you can adjust the feedback resistor value;

(5) After replacing the IC input, the output impedance matches the original PCB circuit, and check its drive capability;

(6) Make full use of the original PCB circuit board pin holes and leads when changing. The external leads are required to be neat and avoid front and back crossing to check and prevent PCB circuit self-stimulation, especially to prevent high-frequency self-excitation;

(7) It is best to connect a DC ammeter in the power supply VCC circuit before power-on, and change the anti-high voltage resistance value from large to small to observe that the total current of the integrated PCB circuit is normal.

6. Use discrete components to replace ICs. Sometimes discrete components can be used to replace damaged parts of ICs to restore functionality. Before replacing, you should understand the internal function principle of the IC, the normal voltage of each pin, the waveform diagram and the working principle of the PCB circuit composed of peripheral components