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Common techniques for PCB board repair

2019-08-07 10:39:14
Since most modern boards do not have official schematics, and there are more and more chips with programs, engineers will face various challenges. Through a lot of practice, there are still ways to face these challenges. Below, I will share the experience of my maintenance over the years with the majority of electronic enthusiasts.

Visual inspection method

That is, through the old method of looking, asking, smelling, and cutting, observe whether the circuit board has burnt place, whether the copper is broken, whether there is any smell on the circuit board, whether there is a bad soldering place, interface, gold finger Is there a phenomenon of mold and blackness? Inquiring about the customer's failure phenomenon and the process of the failure, the focus of the failure can be concentrated on certain parts. Through the above processing, some problems can often be found. Ceramic Flash Gold wholesales.

2. Passing method

All the components will be tested once, and the defective components will be replaced to achieve the purpose of repair. If the components that cannot be detected by the instrument are encountered, the substitution method is adopted, that is, the new components are replaced regardless of whether they are damaged or not. In the end, all the devices on the board are guaranteed to be good for repair. The method is simple and effective, easy to get started, and the technical level of the engineer is not high, but the operation requires a high degree of care and responsibility. Otherwise, some devices do not remember the position when they are removed, and the installation is wrong. It is easy to cause maintenance failure. In addition, this method is powerless for problems such as via failure, copper breakage, and improper adjustment of the potentiometer. This method cannot be used when encountering chips with programs and data.

3. Comparison method

Contrast method is one of the most commonly used methods for repairing circuit boards without drawings. Practice has proved that it has very good effect. By comparing the state of the good board with the purpose of detecting faults, the abnormality is found by comparing the curves of the nodes of the two boards. . However, many times we don't have a good board to compare, but this does not mean that we can't use this method. For example, we can find circuits with the same properties in the board, such as a board with three identical interfaces. The three interfaces have the same circuit, and we can use the three identical interfaces to compare the curves to determine the problem. When we can't find the situation mentioned above, we can still find the circuit of the common attribute. For example, the bus in the circuit usually has the same curve. Sometimes we can't judge whether an IC is damaged. We can also use the curve scan method to compare the curve with a good IC to achieve the purpose of judgment. CERAMIC WAFER manufacturer china.

4. State method

The state method is to check the state of normal operation of each component. If the state of a component does not match the normal state, the device or its affected component has a problem. For example, when we check the CPU, we will check if the crystal oscillator is working properly, whether the reset signal is normal, and so on. Whether the input and output logic of the NAND gate is correct or not is used to judge whether the device is normal. When using this method, the input signal is often forced to be excited. RADIO FREQUENCY BOARD.

5. Substitution method

Replace all ICs with new ones until they are repaired. Nowadays ICs are getting cheaper and cheaper. The 74 series and 4000 series chips are less than 1 yuan/piece cheaper. It is better to replace them with them. This method I personally feel is a helpless move, its shortcomings are also obvious, the effect should be lower than the pass-kill method, the pass-through method must at least judge the device, long-term accumulation will also have some boards Some experience, and the repair rate of the method depends entirely on luck rather than effort, even if it is really repaired, I don't know where the fault is. However, this method still has its merits. If a circuit board or an electronic device can be used on the spot to verify that it is normal, we can replace the IC one by one. When the switch is changed to a certain block, the fault disappears. The piece that just changed was broken. If it is an in-line package IC, it is recommended that you install an IC holder immediately after removal. After all, that thing is only a few cents. Another fatal problem with this method is that you must ensure that the IC you bought is good. If you accidentally encounter a bad IC during purchase, this will not only repair the fault, but will increase the fault and increase the difficulty of repair.