For most circuit boards, problems cannot be found through the previous observation. As long as a small number of circuit boards will cause physical deformation due to some special reasons, and easily find out the cause of the fault. Most of the circuit boards that cause failure need to use the multimeter to have some major components and key points on the circuit board. Preface measurement, find problems, solve problems.

　　Before the measurement, we must first judge whether the circuit is mainly analog signal or a digital signal. For the circuit board with a schematic diagram, you can judge by viewing the schematic diagram. However, for the circuit board without the schematic diagram, the following two methods are generally judged:

　　① Observe the components on the circuit board and see if there are microprocessors on the circuit board. Whether it is the early 80, 51 series, or the currently widely used DSP, as long as such chips appear on the circuit board, it means that there is a bus on the board on the board. The structure, the digital signal will have a large part of it, and it can be treated as a digital board.

　　② For circuit boards without microprocessors, observe the components on the observation board, and there are not many chips that apply 5V power supply. If there are many 5V power chips, it can also be repaired as a digital circuit. The maintenance methods of digital circuits and analog circuits are different. Generally speaking, simulation circuits are easier to repair. You can move forward step by step to find out the problem. However, for digital circuits, because the circuit is hung on the bus, there is no clear subordinate relationship. Therefore, it is more difficult to repair. The following only focuses on the static measurement method of digital circuit. The maintenance mainly follows the following steps:

　　Step 1: Use a multimeter to check whether the power supply is short -circuited.

　　The method of checking is: Find a 5V power supply chip and measure two points on the diagonal (such as 14 -pin chips, measure 7 -pin and 14 -pin chips, and measure 8 -pin and 16 pin). If there is no short circuit between two points, it means that the power work is roughly normal. If a short -circuit phenomenon occurs, the reason is needed to find the reason. These steps are only the basic ideas of power maintenance. Specific to particularly complex circuit boards require specific problems and specific analysis. The power supply is the basis of the circuit. Only when the power work is normal can we talk about the application of subsequent circuits. Therefore, the measurement of the power supply is very important, and it is also a step that is particularly easy to be ignored by the maintenance.

　　Step 2: Use a multimeter to measure the diode to observe whether its work is normal. Under normal circumstances, the positive and negative electrodes are measured with a resistor file. Generally speaking, the diode is damaged, and the current in the circuit is cut off due to the excessive current of the circuit.

　　Step 3: Use a multimeter resistance file to measure the capacitor to see if there is a short circuit or disconnection. If there is, it means that there is a problem with this part of the circuit. In the next step, it is necessary to determine whether there is a problem with the component itself, or there is a problem with the circuit connected to it. The method is to welded the suspicious components to see if there is a disconnection and a circuit breaking. In this way, you can determine the problem in one step.

　　Step 4: Similarly, use a multimeter to measure the integrated circuit, triode, resistance, etc. on the circuit board to see if it meets its own logical performance. If the circuit board includes the bus structure, there will be a lifting resistance row on the bus. The measurement of the resistance row is a very important step. It can be preliminarily inspected to the chip hung on the bus through its quality.

　　After the inspection of the observation method and the static measurement method, most of the problems in the circuit board repair can be solved. It is worth noting that it is necessary to ensure that the power supply is normal and avoid secondary damage to the circuit board after the next step.

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