ElectronICs manufacturers explain the second half of PCB maintenance skills
5、 Maintenance Method of Circuit Board Common Power Short Circuit Fault
During circuit board maintenance, if there is a short circuit in the public power supply, it is often a big problem. Because many devices share the same power supply, each device using this power supply is suspected of short circuit. If there are not many components on the board, the short circuit point can be found by using the "hoe earth" method. If there are too many components, whether the "hoe earth" can hoe to the situation depends on luck. A more effective method is recommended here. With this method, you can get twice the result with half the effort and often find the fault point quickly.
There should be a power supply with adjustable voltage and current. The voltage is 0-30V, and the current is 0-3A. This power supply is inexpensive, about 300 yuan. Adjust the open circuit voltage to the power supply voltage level of the device. First, adjust the current to the minimum. Apply this voltage to the power supply voltage point of the circuit, such as the 5V and 0V terminals of 74 series chips. Slowly increase the current depending on the degree of short circuit. Touch the device with your hand. When you feel that a device is obviously hot, this is often a damaged component. You can take it down for further measurement and confirmation. Of course, during operation, the voltage must not exceed the working voltage of the device, and the connection must not be reversed, otherwise other good devices will be burned.
6、 A SMAll rubber to solve big problems
More and more boards are used in industrial control, and many of them are inserted into the slots with gold fingers Due to the harsh environment of the industrial site and the dusty, humid and corrosive gas environment, it is easy to cause the board to have a bad contact fault. Many friends may solve the problem by replacing the board, but the cost of purchasing the board is very considerable, especially for some imported equipment. In fact, you might as well use an eraser to repeatedly wipe the golden finger, clean up the dirt on the golden finger, and then try the machine again. Maybe it will solve the problem! The method is SIMple and practical.
7、 Analysis of Electrical Faults of Good and Bad
In terms of probability, the electrical faults of good and bad times generally include the following situations:
1. Poor contact
Poor contact between the board and slot, no connection when the cable is broken, poor contact between the cable plug and terminal block, and faulty soldering of components are all included in this category;
2. Signal interference
For digital circuits, under specific conditions, faults will appear. It is possible that the control system is indeed affected by too much interference, and the parameters of individual components or the overall performance parameters of the circuit board have changed, making the anti-interference ability tend to the critical point, thus causing faults;
3. Poor thermal stability of components
From a large number of maintenance practices, the thermal stability of electrolytic capacitor is poor, followed by other capacitors, triodes, diodes, ICs, resistors, etc;
4. There is moisture and dust on the circuit board
Moisture and dust will conduct electricity with resistance effect, and the resistance value will change in the process of thermal expansion and cold contraction. This resistance value has a parallel effect with other components. If this effect is strong, the circuit parameters will be changed, causing faults;
5. Software is also a consideration
Many parameters in the circuit are adjusted by software. The margin of some parameters is adjusted too low, which is in the critical range. When the operating condition of the machine meets the reason for the software to judge the failure, the alarm will appear.
8、 How to quickly find component data?
Modern electronic products are various, and there are more and more components. In circuit maintenance, especially in the field of industrial circuit board maintenance, many components have never been seen or even heard of. In addition, even if the components of a certain type of board have complete data, they should be read and analyzed one by one in the computer. If there is no quick search method, the maintenance efficiency will be greatly reduced, In the field of industrial electronic maintenance, efficiency is money.
PCB manufacturers, PCB designers, and PCBA manufacturers will explain the second half of PCB maintenance skills to you.