According to the experience and insights I gained while repairing the circuit board, I would like to share with you friends. Our friends who have repaired electronic products know that in a complete electronic product, there is usually a piece of circuit board that is placed in different positions in the electrical appliance according to different functions. Its function is different. We play the main function. It is called circuit board, such as induction cooker has circuit board, button display board, etc.; LCD TV has switching power supply board, button receiving display board, TV main board, audio, video, USB interface board, etc. So how do we repair the board? I think the first few points can be learned to really learn to repair the board.
When we are studying maintenance, we often listen to the master saying that “the practice without theory is blind practice.” This sentence shows that you must learn some basic theoretical knowledge of electronics when learning to repair, such as electrical principles, analog circuits, digital circuits, etc., do not need us to study in depth but need us to understand. For example, three kinds of amplifying circuit forms, several circuit feedback forms, two characteristics of the operational amplifier, etc., which play an important role in understanding the circuit diagram.
Also, when repairing the circuit board, learn to detect and identify common electronic components, understand the characteristics of common electronic components, and know their basic functions. For example, the most common component resistance, it can be divided, limited current, coupled, sampled, dummy load, pull-up resistor, pull-down resistor, and capacitor together with the capacitor to form timing, oscillation and so on. The role of these common components is to be understood.
After these studies, you must learn the skills and knowledge of running the circuit board. This is what we often say about mapping boards. Because our extensive maintenance practice shows that most electrical appliances do not have a schematic diagram reference when repairing. In the face of an unfamiliar circuit board, it is only necessary to learn to map the circuit to understand the circuit board.
We must learn to use common instrumentation and welding tools, such as the most common multimeter (pointer or digital), oscilloscope (analog or digital), millivoltmeter, function signal generator and so on. These are commonly used instrumentation for repairing circuit boards. For those with MCU boards, logic analyzers, programming programmers, etc. are also required. In addition to common electrical tools, tools also need hot air guns, welding stations, magnifiers and so on. Having said that, in fact, these are the necessary knowledge and skills to learn to repair circuit boards.
Nowadays, the circuit board is more and more complicated. If you want to learn to repair the circuit board, you need to master at least the following skills: 1. Know all kinds of commonly used electronic components, and measure their quality with a multimeter; 2. Know the symbols of various components. And its role in the circuit, and learn to understand the circuit diagram; 3, will use the soldering iron skilled welding, disassemble various components. Below we introduce the basics of this aspect.
1. Know common components and use a multimeter to measure their quality.
No matter which kind of circuit board is composed of resistors, capacitors, diodes, triodes and ICs of various colors, if you want to learn to repair the circuit board, the above various components must be known. If there is a lack of knowledge in this area, you can only repair some simple faults on the board. For example, a thermistor of a glass case package is commonly used as a temperature sensor in an induction cooker, and the shape of the thermistor is the same as that of the commonly used 1N4148. If the knowledge of related components is lacking, the thermistor is mistaken as a 1N4148 diode. It is impossible to repair the induction cooker.
When repairing circuit boards, such as electrolytic capacitors, diodes, and triodes are fragile components, you must learn to use a multimeter to judge their quality. This basic skill must be mastered. I have seen some circuit board repairers in the factory not using a multimeter to measure the quality of a component. If a component is suspected to be defective, it will be replaced with a new one. As a result, a large number of components will be repaired.
2. Master the basic uses of commonly used components and recognize their circuit symbols
There are all kinds of components on the circuit board. If you don’t know the role in the circuit, it is very difficult to learn to repair the circuit board. For example, the 78L05 in the TO-92 package is a low-current three-terminal regulator IC. Its shape is the same as that of the commonly used 9015 transistor. It is assumed that this regulator IC has not been seen. It is mistaken for an ordinary triode. See the circuit. The 78L05 on the board burns out and is directly replaced with a triode with the same shape and packaging, which may also damage other components on the board.
When repairing a more complicated circuit board, it is generally necessary to look at the circuit schematic. At this time, it is required to recognize the circuit symbols of various components and their connection relationship with other components. If you want to master this knowledge, you can read some books like “How to Understand the Circuit Schematic”.
3, able to use soldering iron to solder and disassemble components
Only the above components knowledge, if the soldering iron is soldered and disassembled components are generally level, it is impossible to become a master of circuit board repair. When repairing the circuit board, some faults are relatively simple. It can be seen that the component is broken by the intuitive method, but the level of the repairer disassembling or soldering the component is too bad, and the copper foil or the soldering pad of the circuit board may be hot. Bad, causing new failures. Especially for double-sided boards, if the pads are burned off and the pads are not repaired, the board may not work properly even if new components are replaced. To improve the level of soldering and disassembling components, it is necessary to solder and disassemble components.