How to understand the circuit board wiring diagram? First of all, let’s first understand the characteristics of the application circuit diagram:

① Most of the application circuits do not draw the internal circuit block diagram, which is not good for the recognition of the diagram, especially for beginners to analyze the circuit work.

②For beginners, it is more difficult to analyze the application circuits of integrated circuits than to analyze the circuits of discrete components. This is the origin of not understanding the internal circuits of integrated circuits. In fact, it is good to read the diagram or repair it. It is more convenient than discrete component circuits.

③For integrated circuit application circuits, it is more convenient to read the diagram when you have a general understanding of the internal circuit of the integrated circuit and the function of each pin. This is because the same types of integrated circuits have regularities. After mastering their commonalities, it is easy to analyze many integrated circuit application circuits with the same function and different types. The methods and precautions of IC application circuit diagram recognition methods and precautions for the analysis of integrated circuits mainly include the following points:
(1) Understanding the function of each pin is the key to identifying the picture. To understand the function of each pin, please refer to the relevant integrated circuit application manual. After knowing the function of each pin, it is convenient to analyze the working principle of each pin and the function of the components. For example: Knowing that pin ① is the input pin, then the capacitor connected in series with pin ① is the input coupling circuit, and the circuit connected to pin ① is the input circuit.

(2) Three methods to understand the role of each pin of an integrated circuit There are three methods to understand the role of each pin of an integrated circuit: one is to consult relevant information; the other is to analyze the internal circuit block diagram of the integrated circuit; the third is to analyze the application circuit of the integrated circuit The circuit characteristics of each pin are analyzed. The third method requires a good circuit analysis basis.

(3) Circuit analysis steps Integrated circuit application circuit analysis steps are as follows:
① DC circuit analysis. This step is mainly to analyze the circuit outside the power and ground pins. Note: When there are multiple power supply pins, it is necessary to distinguish the relationship between these power supplies, such as whether it is the power supply pin of the pre-stage and post-stage circuit, or the power supply pin of the left and right channels; for multiple grounding The pins should also be separated in this way. It is useful for repairing to distinguish multiple power pins and ground pins.

② Signal transmission analysis. This step mainly analyzes the external circuit of signal input pins and output pins. When the integrated circuit has multiple input and output pins, it is necessary to find out whether it is the output pin of the front stage or the rear stage circuit; for the dual-channel circuit, distinguish the input and output pins of the left and right channels.

③Analysis of circuits outside other pins. For example, to find out the negative feedback pins, vibration damping pins, etc., the analysis of this step is the most difficult. For beginners, it is necessary to rely on the pin function data or the internal circuit block diagram.

④After having a certain ability of recognizing pictures, learn to summarize the rules of circuits outside the pins of various functional integrated circuits, and master this rule, which is useful for improving the speed of recognizing pictures. For example, the rule of the external circuit of the input pin is: connect to the output terminal of the previous circuit through a coupling capacitor or a coupling circuit; the rule of the external circuit of the output pin is: connect to the input terminal of the subsequent circuit through a coupling circuit.

⑤When analyzing the signal amplification and processing process of the internal circuit of the integrated circuit, it is best to consult the internal circuit block diagram of the integrated circuit. When analyzing the internal circuit block diagram, you can use the arrow indication in the signal transmission line to know which circuit the signal has been amplified or processed, and the final signal is output from which pin.

⑥ Knowing some key test points and pin DC voltage rules of integrated circuits is very useful for circuit maintenance. The DC voltage at the output of the OTL circuit is equal to half of the DC operating voltage of the integrated circuit; the DC voltage at the output of the OCL circuit is equal to 0V; the DC voltages at the two output ends of the BTL circuit are equal, and it is equal to half of the DC operating voltage when powered by a single power supply. Time is equal to 0V. When a resistor is connected between two pins of an integrated circuit, the resistor will affect the DC voltage on these two pins; when a coil is connected between the two pins, the DC voltage of the two pins is equal. When the time is not equal, the coil must be open; when a capacitor is connected between two pins or an RC series circuit, the DC voltage of the two pins is definitely not equal. If they are equal, the capacitor has broken down.

⑦Under normal circumstances, do not analyze the working principle of the internal circuit of the integrated circuit, which is quite complicated.