First, the failure characteristics of electronic components
Although there are many electronic components in electrical equipment, their failures are regular.
1. Characteristics of resistance damage
Resistors are the most numerous components in electrical equipment, but not the ones with the highest damage rate. The open circuit is the most common damage to the resistance, and it is rare for the resistance value to increase, and it is very rare for the resistance value to decrease. Commonly used are carbon film resistors, metal film resistors, wirewound resistors and fuse resistors.
The first two types of resistors are the most widely used, and the characteristics of their damage are that the damage rates of low resistance (below 100Ω) and high resistance (above 100kΩ) are relatively high, and the intermediate resistance (such as hundreds of ohms to tens of thousands of ohms) has a high damage rate. Very little damage; Second, when the low-resistance resistor is damaged, it is often scorched and blackened, which is easy to find, while the high-resistance resistor is rarely damaged.
Wirewound resistors are generally used for large current limiting, and the resistance value is not large. When the cylindrical wirewound resistor is burned out, some will turn black or the surface will explode, crack, and some will have no traces. Cement resistors are a type of wirewound resistors, which may break when burned out, otherwise there will be no visible traces. When the fuse resistor burns out, some surfaces will blow off a piece of skin, and some will have no traces, but they will never be scorched and blackened. According to the above characteristics, you can focus on checking the resistance and quickly find the damaged resistance.
2. Characteristics of electrolytic capacitor damage
Electrolytic capacitors are used in a large amount in electrical equipment and have a high failure rate. The damage of electrolytic capacitors has the following manifestations: First, the capacity is completely lost or the capacity becomes smaller; the second is slight or serious leakage; the third is the loss of capacity or the decreasing capacity and leakage. The methods to find damaged electrolytic capacitors are:
(1) Look: some capacitors will leak when they are damaged, and there will be a layer of oil on the surface of the circuit board under the capacitor and even the surface of the capacitor. This capacitor must not be used again; some capacitors will bulge after damage, and this capacitor cannot be used. continue to use;
(2) Touch: some electrolytic capacitors with serious leakage will heat up after starting up, and even hot when touching with fingers, such capacitors must be replaced;
(3) There is electrolyte inside the electrolytic capacitor. Baking for a long time will cause the electrolyte to dry out and reduce the capacitance. Therefore, it is necessary to focus on checking the capacitors near the heat sink and high-power components. The closer it is, the more likely it will be damaged. sex is greater.
3. Characteristics of damage to semiconductor devices such as transistors and transistors
Second, the damage of the triode is generally the breakdown or open circuit of the PN junction, among which the breakdown short circuit is mostly. In addition, there are two damage manifestations: one is the deterioration of thermal stability, which is normal when starting up, and soft breakdown occurs after working for a period of time; the other is the deterioration of the characteristics of the PN junction, measured with a multimeter R×1k, Each PN junction is normal, but it cannot work normally after the machine is turned on. If it is measured with R×10 or R×1 low-range gear, it will be found that the forward resistance value of the PN junction is larger than the normal value.
The second and triode can be measured on the road with a pointer multimeter. The more accurate method is: set the multimeter to R×10 or R×1 gear (generally use R×10 gear, and then use R×1 gear when it is not obvious) on the road test. 2. The forward and reverse resistance of the PN junction of the triode, if the forward resistance is not too large (relative to the normal value), and the reverse resistance is large enough (relative to the forward value), it indicates that the PN junction is normal, otherwise it is doubtful and needs to be welded Test later. This is because most of the peripheral resistances of the diodes and transistors in the general circuit are more than hundreds or thousands of ohms, and the influence of the peripheral resistance on the PN junction resistance can be basically ignored when the multimeter is used to measure the low resistance value on the road.
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