First, a small trick for multimeter testing SMT components
Some SMD components are very small and inconvenient to test and repair with ordinary multimeter pens. One is that it is easy to cause a short circuit, and the other is that it is inconvenient for the circuit board coated with an insulating coating to touch the metal part of the component pin. Here is an easy way to tell everyone, it will bring a lot of convenience to the detection.
Take the two smallest sewing needles, (Deep Industrial Control Maintenance Technology Column), close them to the multimeter pen, then take the thin copper wire from a multi-strand cable, and tie the needle and the needle to the Together, use solder to solder firmly. In this way, there is no risk of short circuit when measuring those SMT components with a test pen with a small needle tip, and the needle tip can pierce the insulating coating and hit the key parts directly, without having to bother to scrape the film.
Second, the maintenance method of the circuit board public power supply short circuit fault
In circuit board maintenance, if you encounter a short-circuit of the public power supply, the fault is often serious, because many devices share the same power supply, and every device using this power supply is suspected of short-circuiting. If there are not many components on the board, use “hoe the earth” After all, you can find the short-circuit point. If there are too many components, it will depend on luck to “hoe the earth” to reach the condition. A more effective method is recommended here. Using this method will get twice the result with half the effort and often find the fault point quickly.
It is necessary to have a power supply with adjustable voltage and current, voltage 0-30V, current 0-3A, this power supply is not expensive, about 300 yuan. Adjust the open circuit voltage to the device power supply voltage level, first adjust the current to the minimum, add this voltage to the power supply voltage point of the circuit, such as the 5V and 0V terminals of the 74 series chip, depending on the degree of short circuit, slowly increase the current. Touch the device by hand. When you touch a device that heats up significantly, this is often a damaged component, which can be removed for further measurement and confirmation. Of course, the voltage must not exceed the working voltage of the device during operation, and the connection cannot be reversed, otherwise it will burn out other good devices.
Third. A small eraser can solve big problems
More and more boards are used in industrial control, and many boards use golden fingers to insert into the slots. Due to the harsh industrial site environment, dusty, humid, and corrosive gas environment, the board may have poor contact failures. Friends may have solved the problem by replacing the board, but the cost of buying the board is very considerable, especially the boards of some imported equipment. In fact, you might as well use an eraser to rub the gold finger several times, clean up the dirt on the gold finger, and try the machine again. The problem may be solved! The method is simple and practical.
Forth. Analysis of electrical faults in good times and bad times
In terms of probability, various electrical faults with good and bad times include the following situations:
1. Poor contact
Poor contact between the board and the slot, when the cable is broken internally, it will not work, the plug and the wiring terminal are not in contact, and the components are soldered.
2. The signal is interfered
For digital circuits, faults will only appear under certain conditions. It is possible that too much interference has affected the control system and caused errors. There are also changes in individual component parameters or overall performance parameters of the circuit board to prevent interference. Ability tends to a critical point, which leads to failure;
3. Poor thermal stability of components
From a large number of maintenance practices, the thermal stability of electrolytic capacitors is the first to be poor, followed by other capacitors, triodes, diodes, ICs, resistors, etc.;
4. Moisture and dust on the circuit board.
Moisture and dust will conduct electricity and have a resistance effect, and the resistance value will change during the process of thermal expansion and contraction. This resistance value will have a parallel effect with other components. When this effect is strong, it will change the circuit parameters and cause malfunctions. occur;
5. Software is also one of the considerations
Many parameters in the circuit are adjusted by software. The margins of some parameters are adjusted too low and are in the critical range. When the operating conditions of the machine meet the reasons for the software to determine the failure, then an alarm will appear.
Fifth, how to quickly find component information
Modern electronic products are diverse, and the types of components are becoming more and more diverse. In circuit maintenance, especially in the field of industrial circuit board maintenance, many components are unseen or even unheard of. In addition, even if the information on the components on a certain board is complete, But if you want to browse and analyze these data one by one in your 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, and efficiency is the same as pocket money.