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Common electronic components damage and analysis

o-leading. o-leading.com 2019-02-20 17:43:49

Winter is coming, there is a cold current, some of the body is poor, can not stand the cold and hot changes of the environment, fever, but the strong body is strong, no sick. This shows that illness is related to your own constitution. In the circuit, the strongest body is resistance, inductance, followed by capacitors, semiconductor devices (including diodes, transistors, field tubes, integrated circuits), that is, under the same working conditions, semiconductor devices have the highest probability of damage, so When we look for faulty components, we must first check the diodes, transistors, field tubes, integrated circuits, etc. Generally, when the semiconductor device is damaged, the breakdown is more common. The multimeter diode buzzer test should have a PN junction at least on any two feet of these devices. The resistance is about 500. If the buzzer is 80%, it can be removed and tested to confirm. Different electronic components, the characteristics of damage are different, what is the law of damage to electronic components?

1 resistance damage characteristics
Resistance is the most abundant component in electrical equipment, but it is not the component with the highest damage rate. Resistance damage is the most common with open circuit, the resistance value becomes smaller, and the resistance value becomes very small. Common carbon film resistors, metal film resistors, wirewound resistors and fuse resistors. The first two resistors are the most widely used, and their damage characteristics are low resistance (less than 100Ω) and high resistance (above 100kΩ), and high resistance, intermediate resistance (such as several hundred ohms to tens of thousands of ohms). Very little damage; second, when the low-resistance resistance is damaged, it is often burnt and black, which is easy to find, and there is little trace when the high-resistance resistance is damaged. Wirewound resistors are generally used as current limiting currents with little resistance. When the cylindrical wirewound resistor is burnt out, some may be black or the surface is blasted, cracked, and some have no trace. Cement resistance is a type of wirewound resistor that may break when burnt out, otherwise there are no visible traces. When the fuse is burned out, some surfaces will blow off a piece of skin, and some will have no trace, but it will never burnt and black. According to the above characteristics, when checking the resistance, you can focus on it and quickly find out the damaged resistance.

2 electrolytic capacitor damage characteristics
Electrolytic capacitors are used in large quantities in electrical equipment and have a high failure rate. Electrolytic capacitor damage has the following performances: one is to completely lose capacity or the capacity is small; the other is slight or severe leakage; the third is loss of capacity or capacity and leakage. The methods for finding damaged electrolytic capacitors are:

(1) Look: Some capacitors will leak when they are damaged. There will be a layer of oil on the surface of the circuit board under the capacitor or even the surface of the capacitor. This capacitor can never be used again. Some capacitors will bulge after being damaged. continue to use;

(2) Touch: Some electrolytic capacitors with serious leakage will heat up after starting up, and even hot when touched with fingers, this capacitor must be replaced;

(3) There is electrolyte inside the electrolytic capacitor. If it is baked for a long time, the electrolyte will dry out, resulting in a decrease in capacitance. Therefore, it is necessary to check the capacitance near the heat sink and high-power components. The closer to it, the possibility of damage. The greater the sex.

3, the characteristics of semiconductor devices such as triodes are damaged
Second, the damage of the triode is generally the breakdown or open circuit of the PN junction, in which the breakdown short circuit is mostly. In addition, there are two kinds of damage performance: First, the thermal stability is worse, the performance is normal at booting, soft breakdown occurs after working for a period of time; the other is that the characteristics of the PN junction are deteriorated, measured by a multimeter R×1k, Each PN junction is normal, but it cannot work normally after being put on the machine. If it is measured with R×10 or R×1 low-range, it will find that the positive resistance of its PN junction is larger than the normal value. Measuring the second and triode can be measured on the road with a pointer multimeter. The more accurate method is to set the multimeter to R×10 or R×1 (usually use R×10 files, and then use R×1 files when not obvious) in the road test. Second, the PN junction positive and negative resistance of the triode, if the forward resistance is not too large (relative to normal value), the reverse resistance is large enough (relative to the positive value), indicating that the PN junction is normal, otherwise it is doubtful, need to be welded Then test again. This is because the peripheral resistance of the second and triode of the general circuit is mostly in the hundreds or thousands of ohms. It is measured by the low resistance value of the multimeter, and the influence of the peripheral resistance on the PN junction resistance can be basically ignored.

4 integrated circuit damage characteristics
The internal structure of the integrated circuit is complicated and has many functions, and any part of the damage cannot work normally. There are also two types of damage to integrated circuits: complete damage and poor thermal stability. When it is completely damaged, it can be removed, and the positive and negative resistance of each pin to ground can be measured compared with the normal integrated circuit of the same type. It is always found that one or several of the pins have abnormal resistance. For poor thermal stability, the suspected integrated circuit can be cooled with absolute alcohol while the device is in operation, and can be determined if the time of failure is delayed or no longer occurs. Usually only new integrated circuits can be replaced to eliminate them.
We all know that the scorpion in the early days is bad, and the guards of the heads are ready to sacrifice at any time, which shows that the job position determines the degree of danger. In the circuit, components operating under high voltage, high current, and high power are undoubtedly subjected to large pressures, and are highly likely to be damaged. They are also key components and functional components of the circuit. Where the heat is generated at a large current (the Joule's law - the heat is proportional to the square of the current), so any component with a heat sink is a consumable. High-power resistors are also wearing parts. How can high power resistors be seen? It has nothing to do with its resistance, only related to its volume. The larger the volume, the greater the power. In the circuit, the fuse and the fuse are the most unsafe components. First, because of its low melting point, it is easy to break, and because it is the danger of protecting others, it rushes to the front line and acts as a security guard, so it is bad when it is bad.