After the production of the circuit board is completed, a series of inspection work needs to be carried out on the circuit board. In the case of ensuring the quality of the circuit board, the packaging and delivery will be delivered to the customer. Then for the circuit board production company, the most common seven kinds of inspections are What is the method!
1. look first and then measure: the circuit board to be repaired should be visually inspected first. If necessary, it should be observed with the help of a magnifying glass.
2. first outside and then inside: it is best to have a good circuit board that is the same as the board to be repaired as a reference, and then use the dual-bang VI curve scanning function of the tester to perform a good and bad comparison test on the two boards. The initial comparison test point can be started from the port of the circuit board; then the comparison test of capacitors, especially the capacitors, can make up for the shortcoming that the multimeter is difficult to measure the leakage of capacitors online.
3. Comparison method: The comparison method is one of the most commonly used methods for repairing circuit boards without drawings. Practice has proved that it has a very good effect. The purpose of detecting faults is achieved by comparing the status of the good boards. By comparing the nodes of the two boards curve to detect anomalies. However, many times we do not have a good board to compare, but this does not mean that we cannot use this method. For example, we can find circuits with the same properties in the circuit board. For example, a board has three identical interfaces. The three interfaces have the same circuit, and we can use the three identical interfaces to compare the curves with each other to judge the problem.
4. the state method: The state method is to check the normal working state of each component. If the working state of a component does not conform to the normal state, the device or its affected components have problems. For example, when we check the CPU, we will check whether the crystal oscillator is working normally, whether the reset signal is normal, and so on. Whether the input and output logic of the NAND gate is correct is used to judge whether the device is normal. When using this method, the input is often forced to stimulate the signal. For example, a signal generator is used to give a signal to the input end of the op amp, and the output is measured with an oscilloscope. Signal amplitude and distortion to determine the problem of the op amp. Forcibly push the input level of the logic gate circuit high or low, and test whether its output level conforms to the logic of the chip, so as to judge the quality of the chip. The state method is the most accurate method of all maintenance methods, and its operation difficulty is beyond the grasp of ordinary engineers. It requires rich theoretical knowledge and practical experience. In order to meet the state requirements, engineers must do everything possible. The method is better than the curve scanning method for circuit testing, whether it is the peripheral circuit of the IC or the non-peripheral circuit problem can be found.
5. Substitution method: All ICs are replaced with new ones until they are repaired. Now ICs are getting cheaper and cheaper. 74 series and 4000 series chips are less than 1 yuan per chip. Instead of checking problems one by one, it is better to replace them all. I personally feel that this method is a helpless move, and its shortcomings are also obvious. Its effect should be lower than that of the pass-kill method. The pass-kill method at least needs to judge the device. If it accumulates for a long time, it will also have some problems on some circuit boards. Some experience, and the repair rate of this method depends entirely on luck rather than effort, and even if it does repair, I don't know where the fault is. However, this method still has its merits. If a certain circuit board or electronic device can be used to verify whether it is normal or not, we can replace the IC piece by piece. The one I just replaced is broken. If it is an in-line packaged IC, it is recommended that you install an IC seat immediately after removing it. 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 when purchasing, it will not only fail to repair, but will expand the fault and increase the difficulty of repair.
6. the circuit method: the circuit method is to make a circuit by hand. The circuit can work after installing the missing integrated circuit, so as to verify the quality of the tested integrated circuit. For example, in order to judge the quality of a 555 integrated circuit, We can build a time base oscillation circuit made of 555 circuit, and then place the integrated circuit under test in the circuit. If the circuit works normally, it proves that there is no problem with the 555, otherwise it is faulty.
7. Principle analysis method: This method is to analyze the working principle of a board. For some boards, such as switching power supply, engineers can know their working principle and details without drawings. For engineers, they can know their schematic diagrams. Repairs are exceptionally easy. However, for some relatively complex and rare equipment, there is no ready-made schematic reference, so it can be reverse-engineered manually, and the schematic diagram can be drawn. With the schematic diagram, it can be said to be invincible.
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