Circuit boards are widely used in the electronics and IT industries, and the study of their knowledge is a very meaningful subject. So how much do you know about circuit boards? Below is the knowledge about circuit boards compiled by the learning editor, I hope you like it!

　　Circuit boards are divided into three categories according to the number of layers: single-sided boards, double-sided boards, and multilayer circuit boards.

　　One is a single-sided board. On a basic PCB, the components are concentrated on one side, and the wires are concentrated on the other side. Because the wires only appear on one side, this PCB is called a single-sided circuit board. Single-sided boards are usually simple to manufacture and low in cost, but the disadvantage is that they cannot be used in too complex products.

　　Double-sided boards are an extension of single-sided boards. When single-layer wiring cannot meet the needs of electronic products, double-sided boards must be used. Both sides have copper-clad wires, and the lines between the two layers can be connected through vias to form the required network connection.

　　A "multilayer board" refers to a printed circuit board in which three or more conductive graphic layers are sandwiched between insulating materials, and the conductive graphics are interconnected as required. Multilayer circuit boards are products of the development of electronic information technology towards high speed, multi-function, large capacity, small size, thinness, and lightweight.

　　Circuit boards are divided into flexible boards (FPC), rigid boards (PCB), and rigid-flex boards (FPCB) according to their characteristics.

　　 Chip with program

　　1. EPROM chips are generally not prone to damage because these chips need to use ultraviolet light to erase the program, so the program will not be damaged during the testing process (long time), even if it is not used, it may be damaged (mainly refers to the program), so it is best to back up.

　　2. EEPROM, SPROM, etc., and RAM chips with batteries are very easy to damage the program. There is currently no conclusion on whether the program is damaged after using these chips by scanning the VI curve method. However, colleagues have encountered this situation, so it is better to be careful. The author has done many experiments, and the possible reason is: leakage of the repair tools (such as testers, soldering irons, etc.).

　　3. For chips with batteries on the circuit board, do not easily remove them from the circuit board.

　　 Reset circuit

　　1. When there are large-scale integrated circuits on the circuit board to be repaired, pay attention to the reset issue.

　　2. Before testing, it is best to put the equipment back in place, repeatedly turn it on and off, and press the reset button multiple times.

　 　Basic steps for circuit board repair

　　(1) Fault detection: First, it is necessary to use testing instruments and tools to detect the circuit board for faults. By measuring voltage, current, and signal parameters, the location and cause of the fault can be determined.

　　(2) Component replacement: Once the faulty component is identified, it needs to be replaced with a new component. This requires certain skills and soldering techniques to ensure that the component is correctly connected to the circuit board.

　　(3) Soldering repair: If welding connections are found to be defective, the solder joints need to be re-soldered or repaired.

　　This may involve using soldering tools and techniques to ensure a strong and reliable solder connection.

　　(4) Testing and verification: After the repair is completed, the circuit board needs to be tested and verified to ensure that the repaired circuit board is working properly. This can be done by connecting the power supply, inputting signals, etc.

　 　Circuit board repair precautions

　　(1) Safety first: When repairing circuit boards, be sure to disconnect the power supply to avoid safety hazards such as electric shock.

　　(2) Repair tools: Prepare the necessary repair tools, such as soldering tools, testing instruments, magnifying glasses, etc., for fine repair operations.

　　(3) Technical knowledge: Circuit board repair requires certain technical knowledge and experience. If you are not familiar with circuit board repair, it is recommended to seek help from professionals to avoid further damage to the equipment.

　　(4) Anti-static: When handling circuit boards, pay attention to preventing the generation and release of static electricity to avoid damaging sensitive electronic components.

　 　Function and parameter testing

　　1. Equipment detection can only reflect the cutoff region, amplification region, and saturation region, but cannot measure specific values such as operating frequency and speed.

　　2. Similarly, for TTL digital chips, only the changes in high and low outputs can be known, but the speed of the rising edge and falling edge cannot be detected.

　 　Crystal oscillator

　　1. Generally, it can only be tested with an oscilloscope (crystal needs power supply) or a frequency counter.

　　2. Common crystal oscillator faults include: a, internal leakage, b, internal open circuit, c, degradation frequency deviation, d, external capacitor leakage, leakage. The VI curve of the tester should be able to measure it.

　　3. There are two methods for judging the entire board test: a. When testing, the surrounding chips near the crystal oscillator all fail, b. No other fault points are found except for the crystal oscillator.

　　4. Common crystals include a, two-pin, b, four-pin. The two-pin is powered by the power supply, and care should be taken not to short-circuit it casually.

　 　Fault phenomenon distribution

　　1. Incomplete statistics of circuit board fault locations: 1) Chip damage 30%, 2) Discrete component damage 30%, 3) Wire (PCB board copper wire) breakage 30%, 4) Program damage or loss 10% (increasing trend).

　　2. From the above, it can be seen that when the wiring and program of the circuit board to be repaired have problems, and there is no good board at hand, and the wiring is not familiar, and the original program cannot be found, the possibility of repairing the board is not high.