Detailed analysis of the damage rules of components

All electronic devices such as washing machines, refrigerators, air conditioners, computers, instruments, meters, automotive electronics, etc. are all composed of various electronic circuits with different functions. The basic unit of electronic circuits is electronic components, which have their own electrical parameters, such as voltage and current and power characteristics. Components are the most vulnerable items, but their failures are regularly ruled. The general faults are manifested by electrical parameter damage and physical damage. The damage of the electrical parameters includes the damage caused by the voltage and current exceeding the rated value. The physical damage includes the deformation, deformation, and resistance parameter changes.

First, the characteristics of resistance damage

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 as follows: First, low resistance (less than 100Ω) and high resistance (above 100kΩ) have high damage rate, intermediate resistance (such as several hundred ohms to several tens of kilo ohms) Very little damage; the second is that the low-resistance resistance is often burnt and black, it is easy to find, and the high-resistance resistance has few traces when it 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 have a surface blast, crack, and some have no trace. Cement resistance is a kind of wirewound resistor that may break when burnt out, otherwise there will be no visible traces. When the fuse is burned out, some surfaces will blow up 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.

Second, the characteristics of electrolytic capacitor damage

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 becomes smaller;

Second, slight or severe leakage;

The third is the 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.

Third, the characteristics of semiconductor devices such as diodes and transistors

The damage of the triode is generally a breakdown or open circuit of the PN junction, with a breakdown short circuit. 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 can't work normally after being put on the machine. If it is measured with R×10 or R×1 low-range, it will find that its PN junction forward resistance is larger than normal.

Measuring the second and third transistors can be measured on the road with a pointer multimeter. The more accurate method is:

Set the multimeter to R×10 or R×1 (usually use R×10 files, then use R×1 files when it is not obvious). Test the PN junction positive and negative resistance of the second and triodes. If the forward resistance is not too good. Large (relative to normal value), the reverse resistance is large enough (relative to the positive value), indicating that the PN junction is normal, and vice versa, it is doubtful that it needs to be measured after soldering. This is because the peripheral resistance of the second and triode of the general circuit is mostly several hundred or several thousand ohms. It can be 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.

Fourth, the characteristics of integrated circuit damage

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. 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.