PCB News - Static measurement method of PCB board

For most PCB board, the problem cannot be found through the previous observation method. As long as a small part of the circuit board is physically deformed due to some special reasons, it is easy to find the cause of the failure. Most of the circuit boards that have failed still need to use a multimeter to measure some of the main components and key points on the circuit board. Orderly measure, discover and solve problems.

Before the measurement, we must first determine whether the circuit is based on analog signals or digital signals. For a PCB board with a schematic diagram, it can be judged by looking at the schematic diagram. But for a PCB board without a schematic diagram, it is generally judged by the following two methods: 1. Observe the components on the PCB board to see if there is a microprocessor on the circuit board, whether it is the early 80, 51 series or the current wide range For the applied DSP, as long as such a chip appears on the PCB board, it means that there is a bus structure on the board, and the digital signal must occupy a large part of it, and it can be treated as a digital board. 2. For the circuit board without a microprocessor, observe the components on the board to see if there are many chips using 5V power supply. If there are many 5V power chips, you can also use it as a digital circuit for repair. The maintenance methods for digital circuits and analog circuits are different. Generally speaking, the maintenance of analog circuits is simpler. You can deduce step by step to find out the problem. But for digital circuits, since the circuits are all hung on the bus, there is no clear upper-lower relationship. Therefore, maintenance is more difficult. The following only focuses on the static measurement method of digital circuits. Maintenance mainly follows the following steps.

The first step: Use a multimeter to check whether there is a short circuit between the power supply and the ground.

The way to check is: find a chip powered by a 5V power supply and measure two points on the diagonal (for example, a chip with 14 pins, then measure 7 and 14 pins.

16-pin chip, then measure 8 pins and 16 pins). If there is no short circuit between the two points, the power supply is generally working normally. If a short circuit occurs, you need to find the cause through the troubleshooting method.

These steps are only the basic idea of power supply maintenance, and specific problems need to be analyzed in detail for particularly complex circuit boards.

The power supply is the foundation of the circuit. Only when the power supply is working properly can we talk about the application of the subsequent circuit. Therefore, the measurement of the power supply is very important, and it is also a step that is especially easy to be overlooked by maintenance workers.

Step 2: Use a multimeter to measure the diode and observe whether it works normally. Under normal circumstances, the resistance profile is used to measure the positive and negative poles. The positive phase measurement is tens to hundreds of ohms, and the reverse phase is one thousand to several thousand ohms. Generally speaking, when the diode is damaged, the diode is broken down due to the excessive current in the circuit.

The third step: Use the resistance file of the multimeter to measure the capacitance to see if there is a short circuit or open circuit. If there is, it means that there is a problem with this part of the circuit. The next step is to determine whether there is a problem with the component itself or the circuit connected to it. The method is to solder one foot of the suspicious component to see if the component is open or disconnected. In this way, the problem can be determined in one step.

Step 4: Use a multimeter to measure the integrated circuits, transistors, resistances, etc. on the circuit board to see if they meet their own logic performance. If the circuit board includes a bus structure, generally there will be a pull-up resistor row on the bus. The measurement of the resistance row is a very important step. Through its quality, the quality of the chip hanging on the bus can be preliminarily tested.

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

The above is the static measurement method of PCB board. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.