Despite the number of electronic components inside electrical equipment, their failures are regular.

1. Characteristics of resistance damage

Resistor is a large number of components in electrical equipment, but it is not a component with high damage rate. Open circuit is common for resistance damage, it is rare for the resistance to become larger, and it is rare for the resistance to become smaller. There are carbon film resistors, metal film resistors, wire wound resistors and insurance resistors. The first two types of resistors are widely used. One of the characteristics of their damage is that the damage rate of low resistance (below 100Ω) and high resistance (100kΩ) is high, and the resistance value (such as hundreds of ohms to tens of kiloohms) is rarely damaged. Second, when low-resistance resistors are damaged, they are often burnt and blackened, which is easy to find, while high-resistance resistors are rarely damaged. Wire-wound resistors are used for high-current limiting, and the resistance is not large. When cylindrical wire wound resistors burn out, some will turn black or the surface will burst or crack, and some will have no traces. Cement resistor is a kind of wire wound resistor, it will break when burned out, otherwise there will be no visible trace. When the fuse resistor is burned out, a piece of skin will be blown off on some surfaces, and some have no traces, but they will never burn or turn black. According to the characteristics, you can focus on checking the resistance and quickly find the damaged resistance.

2. The characteristics of electrolytic capacitor damage

The amount of electrolytic capacitors used in electrical equipment is large, and the failure rate is high. Electrolytic capacitor damage has the following manifestations:

One is to lose capacity or decrease in capacity;

Two is slight or serious leakage;

The third is the loss of capacity or the reduction of 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 or even on the surface of the capacitor. This type of capacitor must not be used anymore; some capacitors will bulge after damage, and this type of capacitor cannot Continue to use; therefore, when choosing capacitors in the early stage, you should check the quality and try to choose branded capacitors, such as capacitor giants-Yageo capacitors.

(2) Touch: After starting up, some electrolytic capacitors with serious leakage will heat up, and they will even be hot when touched with fingers. Replace this type of capacitor;

(3) There is electrolyte inside the electrolytic capacitor. Long-time baking will make the electrolyte dry and reduce the capacitance. It is important to check the capacitors near the heat sink and high-power components. The closer they are, the possibility of damage The bigger.

3. Damage characteristics of semiconductor devices

The damage of the diode and the triode is the breakdown or open circuit of the PN junction, among which the breakdown short circuit is the majority. In addition, there are two kinds of damage performance: one is the deterioration of thermal stability, which is normal when the machine is turned on, and soft breakdown occurs after a period of operation; the other is the deterioration of the characteristics of the PN junction, measured with a multimeter R×1k, All PN junctions are normal, but they can't work normally after using the machine. If you use R×10 or R×1 low-range measurement, you will find that the forward resistance 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 (use R×10, and then use R×1 when it is not obvious). , The forward and reverse resistance of the PN junction of the transistor, the forward resistance is not too large (normal value), and the reverse resistance is large enough (forward value), indicating that the PN junction is normal, otherwise it is questionable, and it needs to be welded before testing . This is that the peripheral resistance of the diode and triode of the circuit is mostly in the hundreds or thousands of ohms. The low resistance value file of the multimeter is used to measure the circuit, and the influence of the peripheral resistance on the PN junction resistance can be basically ignored.

4. The characteristics of integrated circuit damage

The internal structure, function, and part of the integrated circuit 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 compared with the normal integrated circuit of the same model to test the forward and reverse resistance of each pin to the ground, and one or several pins can always find abnormal resistance. For those with poor thermal stability, you can use absolute alcohol to cool the suspected integrated circuit while the equipment is working, and the failure time will be delayed or the failure will no longer occur. Usually it can only be eliminated by replacing the new integrated circuit.