PCB must know the maintenance skill

- Dec 15, 2017-

The function of the capacitor in the circuit is different, and the fault caused by the capacitor has its own characteristics. In the industrial control circuit board, the digital circuit occupies the most, the capacitance is used as the power filter, and the capacitance of the signal coupling and oscillating circuit is less. Electrolytic capacitor used in the switching power supply, switching power supply if damaged, may not vibrate, no output voltage or output voltage; filtering circuit is not good, due to voltage instability and the occurrence of logical confusion, as when the machine is good or bad or not open the machine, if the capacitance between the power supply and the number of positive and negative word circuit so, failure.

The life of capacitance is directly related to the temperature of the environment. The higher the ambient temperature, the shorter the life span of the capacitor. This rule not only applies to electrolytic capacitors, but also to other capacitors. Some of the capacitors are more serious, and they are even hot when they are touched with their fingers. This capacitance must be replaced.

In the case of bad failure during maintenance, the general majority of the fault caused by capacitor damage is generally excluded from the possibility of bad contact. So in the encounter this kind of fault, the capacitor may be key to check, replace the capacitor often surprise (of course also should pay attention to the quality of the capacitor, to choose the better brands, such as ruby, KINGBOX).

Resistance is the most important element in electrical equipment, but it is not the most damaged element. The resistance damage is most common in the open way, and the obstruction value is rare, and the resistance is very rare. When a cylindrical wire is burned around a resistance, some will be blackened or surface detonating, crack, and some no trace. Cement resistance is a kind of wire wound resistance, it may break when burned, otherwise there is no visible trace. When the insurance resistance is burned, some surface will blow up a piece of skin, and there is no trace, but it will never burn black. According to the above features, the resistance of the resistance can be found quickly when the resistance is checked.

The ideal operational amplifier with the virtual short circuit and opening "characteristics, these two characteristics are very useful for the analysis of linear amplifier circuit. In order to ensure linear application, operation and amplifier must work under closed loop (negative feedback). If there is no negative feedback, the open loop amplifier becomes a comparator. If you want to judge the quality of the device, you should first divide the device into the amplifier or the comparator in the circuit.

From the picture we can see that regardless of what type of amplifier, a feedback resistor Rf, we can check the feedback resistor from the circuit in maintenance, with a multimeter check between the output and the inverting input of the resistance, if the ridiculously large, such as a few M above, we it certainly is to do with the comparator device, if the resistance of 0 ohms to tens of smaller K, then look up whether the resistance is connected between the output and the inverting input, some words do amplifier. According to the principle of virtual short amplifier, that is to say if the operational amplifier is normal, the noninverting input and the inverting input voltage must equal.

The circuit board repair, if the fault of short circuit often encounter public head, because many devices share the same power supply, each with the power supply device has a short circuit of the suspects, if not the element plate, the "big" means it can find the fault point, if the components too much. "CHUDADI can not rely on luck to hoe it. In this way, a comparative method is recommended. This method uses this method to get twice the result and often find the fault point very quickly.

More and more industrial control board is used, many board uses the finger inserted into the slot way. Because of bad environment, dust, damp and corrosive gas environment to board the contact fault, a lot of friends may be through the replacement card way to solve the problem, but the purchase card cost is very considerable, especially some imported equipment board. In fact, you might as well use eraser to wipe repeatedly on the gold fingers, clean up the dirt on the fingers, then try the machine again, and it will solve the problem. It's simple and practical.

All kinds of modern electronic products, components are much more and far more than thousands, in circuit maintenance, especially industrial circuit board maintenance field, many components are seen, or even an unheard of, in addition to hand board components of the complete information, but in the computer will read these data one by one analysis, if not a quick search the law, while the maintenance efficiency will be greatly reduced, the industrial electronic maintenance field, efficiency is money, efficiency is not to go through with pocket money.

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