Circuit diagram of the whole machine and its reading method

1. Functions of the whole machine circuit diagram

The whole machine circuit diagram has the following functions:

① It shows the circuit structure of the whole machine, the specific form of each unit circuit and the connection method between them, thereby expressing the working principle of the whole machine circuit. This is the most complex circuit diagram among the circuit diagrams.

② It gives the specific parameters of each component in the circuit, such as model, nominal value and other important data, which provides a basis for detecting and replacing components. For example, when replacing a transistor, you can find out by referring to the transistor model mark in the figure.

③ Many whole machine circuit diagrams also give the DC working voltage of the relevant test points, which provides convenience for repairing circuit faults. For example, the DC voltage mark on each pin of the integrated circuit, the DC voltage mark on each electrode of the transistor, etc., all provide convenience for repairing these parts of the circuit.

④ It gives useful information related to drawing recognition. For example, through the name of each switch and the mark of the switch position in the figure, you can know the function and current switch state of the switch; when the whole machine circuit diagram is divided into multiple drawings, the mark of the lead connector can easily connect the circuits between the drawings. In some whole machine circuit diagrams, the markings of various switch components are gathered together and marked somewhere on the drawing. The function description of the switch is marked. If you don’t understand a certain switch when reading the drawing, you can check this part of the description.

2. Characteristics of whole machine circuit diagrams

Compared with other circuit diagrams, the whole machine circuit diagram has the following characteristics:

① It includes all the circuits of the whole machine.

② The unit circuits in the whole machine circuits of different models of machines are very rich, which makes it difficult to read the diagram and requires a more comprehensive knowledge of circuits. The whole machine circuit diagrams of the same type of machines have similarities, but they are very different between different types of machines.

③ There are certain rules for drawing the unit circuits of each part in the whole machine circuit diagram. Understanding these rules is beneficial to reading the diagram. The distribution rules are generally: the power supply circuit is drawn at the bottom right of the whole machine circuit diagram; the signal source circuit is drawn on the left side of the whole machine circuit diagram; the load circuit is drawn on the right side of the whole machine circuit diagram; the amplifier circuits of each level are arranged from left to right, and the left and right channel circuits in the two-channel circuit are arranged up and down; the components in each unit circuit are relatively concentrated together.

3. Methods and precautions for reading the whole machine circuit diagram

The following are the precautions for reading the whole machine circuit diagram:

① The analysis of the whole machine circuit diagram mainly includes: the specific location of each unit circuit in the whole machine circuit diagram; the type of unit circuit; the analysis of the DC working voltage supply circuit; the analysis of the AC signal transmission; and the analysis of the working principles of some unit circuits, which are unprecedented and relatively complex.

② For the whole machine circuit diagram divided into several drawings, you can read them one by one. If you need to analyze the entire signal transmission system, you need to connect the drawings for analysis.

③ For the reading of the whole machine circuit diagram, after learning the unit circuit of a function, you can find the unit circuit of this function in several whole machine circuit diagrams and analyze them. Since there are many changes in the unit circuits in the whole machine circuit diagram, and the drawing method of the circuit is affected by other circuits and may not be the same as the single drawn unit circuit, it increases the difficulty of reading the diagram.

④ In general, the direction of signal transmission is from the left side to the right side of the whole machine circuit diagram.

⑤ The reading direction of the DC working voltage supply circuit is from right to left, and the reading direction

of the DC circuit of a certain amplifier circuit is from top to bottom. ⑥ In the process of analyzing the whole machine circuit, if it is difficult to analyze a certain unit circuit, such as the analysis of a certain type of integrated circuit application circuit, you can look up the reading data of this type of integrated circuit (internal circuit block diagram, pin function, etc.) to help read the diagram.

⑦ There will be many English annotations in some whole machine circuit diagrams. It is very helpful to understand the meaning of these English annotations. The English description marked near a certain type of integrated circuit is the functional description of the integrated circuit.