PCB News - How to restore circuit diagram by Printed Circuit Board?

How to restore circuit diagram by Printed Circuit Board?

In case of electronic products without drawings, it is necessary to draw the circuit schematic diagram according to the real object.

There are the following points:

1. Select components with large volume and many pins that play a major role in the circuit, such as integrated circuits, transformers, transistors, etc. to draw reference parts, and then draw from each pin of the selected reference parts to reduce errors.

2. If the printed circuit board is marked with component serial numbers (such as vd870, r330, c466, etc.), because these serial numbers have specific rules, 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. Correctly distinguishing the components of the same functional unit is the basis of drawing layout.

3. If the serial number of components is not marked on the printed board, it is best to number the components themselves in order to facilitate circuit analysis and calibration. When designing the printed board arrangement of components, the manufacturer generally arranges the components of the same functional unit in a relatively centralized manner in order to minimize the copper foil routing. After finding the core device 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 the printed board. Taking the power supply circuit as an example, the negative end of the rectifier connected to the secondary of the power transformer is the positive end of the power supply, and a high-capacity filter capacitor is generally connected with the ground wire, and the capacitor shell is marked with polarity. The power and ground wires can also be found from the three terminal regulator pins. In order to prevent self excitation and anti-interference during printed board wiring, the factory generally sets the widest ground wire copper foil (high-frequency circuits often have large-area grounding copper foil), followed by power wire copper foil and signal wire copper foil. In addition, in electronic products with both analog and digital circuits, their ground wires are often separated on the printed board to form an independent grounding grid, which can also be used as the basis for identification and judgment.

5. In order to avoid too many pin connections of components and parts, so that the wiring of the circuit diagram is crossed and interspersed, resulting in the chaotic drawing, the terminal marks 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 drawing a sketch, it is recommended to use transparent drawing paper, and draw the ground wire, power wire, signal wire, components, etc. by color with multi-color pen. When modifying, gradually deepen the color to make the drawing intuitive and eye-catching, so as to analyze the circuit.

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

8. When drawing the circuit diagram, try to find the circuit diagram of similar products for reference, which will double the work with half the effort.

These are the basic skills of an e-worker.

iPCB .com hopes it's can help you.