PCB Reverse Engineering
The imitation PCB board is a PCB copy board, which is also a PCB clone, which is the PCB reverse engineering to design. First, the components on the PCB circuit board are removed to make a BOM sheet, and the empty board is scanned into an image and processed by the board copying software to restore the PCB board drawing file; the PCB board drawing file is sent to the PCB board factory to make the board ( PCBA), and then add the components (the corresponding components are purchased according to the BOM order) is the same PCB circuit board as the original PCB circuit board.
When we get a product, many times, we don’t have circuit diagrams. So, in this case, how do we tell the principle and working conditions of the circuit board? This is to restore the physical object to the circuit schematic diagram.
When encountering some small physical objects, or when there is a need, when meeting electronic products without drawings, you need to draw a circuit schematic diagram based on the physical objects. This is to reverse the physical objects to the circuit schematic diagram. Although it becomes very complicated in the case of a larger scale, after mastering the following points, I believe we can still do it. For simpler circuits, it is not a problem.
- Select the components such as integrated circuits, transformers, transistors, etc., which are large and have many pins and play a significant role in the loop, and then draw the reference parts, and then start drawing from the selected reference parts to reduce errors.
- If the serial number is marked on the printed board (such as VD870, R330, C466, etc.) because these serial numbers have specific rules, the components with the same first Arabic numerals after the English alphabet belong to the same functional unit, so they should be used when drawing. Correctly distinguishing the parts of the same functional group is the basis of drawing layout.
- If the serial number of the component is not marked on the printed board, it is best to number the component by yourself to facilitate the analysis and proofreading of the circuit. When designing printed circuit board components, the manufacturer generally arranges the elements of the same functional unit relatively in order to minimize the copper foil traces. Once you find a device that plays a central role in a group, you can find other components of the same functional unit as long as you follow the vine.
- Correctly distinguish the ground wire, power wire, and signal wire of the printed board. Taking the power circuit as an example, the negative terminal of the rectifier tube connected to the secondary of the power transformer is the positive electrode of the power supply, and a large-capacity filter capacitor is generally connected to the ground wire. The capacitor shell has a polarity sign. You can also find the power line and ground line from the three-terminal regulator pin. To prevent self-excitation and anti-interference when the factory is wiring the printed board. The copper foil of the ground wire is generally set to be the widest (high-frequency circuits often have large-area grounded copper foil), followed by the copper foil of the power line, and the signal cable The foil is the narrowest. Also, in electronic products with both analog circuits and digital circuits, the printed circuit boards often separate their ground lines to form an independent ground network, which can also be used as a basis for identification and judgment.
- In order to avoid excessive wiring of component pins, the installation of the circuit diagram is interspersed, resulting in messy drawings, the power supply, and the ground wire can use a large number of terminal labels and ground symbols. If there are many components, each unit circuit can also be drawn separately and then combined together.
- When drawing sketches, it is recommended to use transparent tracing paper and use multi-color pens to draw ground lines, power lines, signal lines, components, etc. by color. When modifying, gradually deepen the color to make the drawing intuitive and eye-catching in order to analyze the circuit.
- Master the elemental composition and classic drawing methods of some unit circuits, such as rectifier bridge, voltage stabilizing circuit and operational amplifier, digital integrated circuit, etc. First, draw these unit circuits directly to form the framework of the circuit diagram, which can improve the efficiency of drawing.
- When drawing circuit diagrams, you should find circuit diagrams of similar products as much as possible for reference, which will do more with less.