When you get a product, there is often no circuit diagram. In this case, how to explain clearly the principle and operation of the circuit board?

This is to restore the physical circuit diagram.

When we meet some small objects or electronic products without drawings, we need to draw the circuit diagram according to the objects. There are the following points

1. Select the components with large volume, many pins and playing a major role in the circuit, such as integrated circuits, transformers, transistors, etc. as the drawing reference, and then start drawing from each pin of the selected reference, which can reduce errors.

2. If the printed circuit board is marked with component serial numbers (such as vd870, r330, c466, etc.), due to the specific rules of these serial numbers, the components with the same Arabic numerals after the English letters belong to the same functional unit, so they should be used skillfully in drawing. It is the basis of drawing layout to distinguish the components of the same functional unit correctly.

How to restore the printed circuit board to its schematic diagram

3. If the serial number of components is not marked on the printed circuit board, it is better to number the components for the convenience of analyzing and proofreading the circuit. In order to make the copper foil routing shortest, the components of the same functional unit are generally arranged in a relatively centralized way when designing the components of PCB. After finding the core components of a unit, you can find other components of the same functional unit as long as you follow the steps.

4. Correctly distinguish the ground wire, power wire and signal wire of PCB. Taking the power supply circuit as an example, the negative end of the rectifier tube connected to the secondary of the power transformer is the positive end of the power supply, and a large capacity filter capacitor is generally connected between the rectifier tube and the ground wire. You can also find the power line and ground wire from the three terminal regulator pin. In order to prevent self excitation and anti-interference, the copper foil for ground wire is usually set as wide as possible (for high-frequency circuits, there is usually a large area of grounding copper foil), followed by the copper foil for power line and the narrowest for signal line. In addition, in electronic products with both analog and digital circuits, the ground wires of printed circuit boards are often separated to form an independent grounding grid, which can also be used as the basis for identification and judgment.

5. In order to avoid too much pin wiring of components, which makes the wiring of circuit diagram cross and interpenetrate, resulting in disordered drawing, terminal marking and grounding symbols can be widely used for power supply and ground wire. If there are many components, each unit circuit can be drawn separately and then combined together.

6. When sketching, it is recommended to use transparent tracing paper, and use multi-color pen to draw ground wire, power line, signal line, components, etc. according to color classification. When modifying, the color should be deepened gradually to make the drawing visual and eye-catching, so as to analyze the circuit.

7. Master the basic composition form and classical drawing method of some unit circuits, such as rectifier bridge, voltage stabilizing circuit, operational amplifier, digital integrated circuit, etc. First of all, these unit circuits are directly drawn to form the framework of the circuit diagram, which can improve the drawing efficiency.

8. When drawing the circuit diagram, we should try our best to find the circuit diagram of similar products for reference, which will make half the effort.

These are the basic skills of an electronic worker.

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