Analysis of fault characteristics of electronic components

Although there are a large number of electronic components in electrical equipment, there are some rules to follow.

1. Characteristics of resistance damage

Resistance is a large number of components in electrical equipment, but it is not a component with high damage rate. Resistance damage is common in open circuit, and it is rare for resistance value to increase, but it is rare for resistance value to decrease. There are carbon film resistance, metal film resistance, wire wound resistance and safety resistance. The first two kinds of resistors are widely used, and their damage characteristics are as follows: first, the damage rate of low resistance (below 100 Ω) and high resistance (100k Ω) is relatively high, and the resistance (such as hundreds to tens of thousands of Ω) is rarely damaged;

Second, the low resistance resistance is often burnt and blackened when it is damaged, which is easy to find, while the high resistance has little trace when it is damaged. The winding resistance is used for large current limiting, and the resistance is not large. When the cylindrical wound resistance is burnt out, some will be blackened or the surface will be cracked, some will not have any trace. Cement resistance is a kind of wire wound resistance, which will break when burned out, otherwise there is no visible trace. When the safety resistor is burnt out, some surfaces will blow off a piece of skin, and some have no traces, but they will never scorch and blacken. According to the characteristics, when checking the resistance, we can focus on it to find out the damaged resistance quickly.

2. Characteristics of electrolytic capacitor damage

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

One is the loss of capacity or smaller capacity;

Second, slight or serious leakage;

The third is the loss of capacity or smaller capacity with leakage.

Methods to find the damaged electrolytic capacitor are as follows:

(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 below the capacitor or even on the surface of the capacitor, so the capacitor can't be reused; some capacitors will bulge when they are damaged, and the capacitor can't be used any more; therefore, when selecting the capacitor in the early stage, we should control the quality and try to choose the capacitor of famous brand, such as Guoju power, a giant capacitor Rong.

(2) Touch: after power on, some electrolytic capacitors with serious leakage will get hot, even hot hands when touching with fingers, so this kind of capacitor can be replaced;

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

3. Damage characteristics of semiconductor devices

2、 The damage of triode is the breakdown or open circuit of PN junction, especially the breakdown and short circuit. In addition, there are two kinds of damage: one is poor thermal stability, which is normal when starting up and soft breakdown occurs after working for a period of time; the other is poor characteristics of PN junction, which is measured with a multimeter R × 1K, and all PN junctions are normal, but they can't work normally after being on the computer. If R × 10 or R × 1 low range gear is used, it will be found that the positive resistance of PN junction is larger than the normal value.

The more accurate method is: set the multimeter at R × 10 or R × 1 (use R × 10, use R × 1 when it is not obvious) to measure the forward and reverse resistance of the PN junction of the two and three diodes. The forward resistance is not too large (normal value), and the reverse resistance is large enough (positive value), which indicates that the PN junction is normal. Otherwise, it is doubtful, and it needs to be welded Test again. This is the circuit's diodes and triodes, most of the peripheral resistance in the hundreds, thousands of ohm, with a multimeter low resistance gear in the road measurement, can basically ignore the impact of peripheral resistance on the PN junction resistance.

4. Characteristics of IC damage

Integrated circuit internal structure, function, part of the damage can not work properly. There are two kinds of IC damage: 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. By measuring the forward and reverse resistance of each pin to the ground, one or several pins can always be found with abnormal resistance. If the thermal stability is poor, the suspected IC can be cooled with anhydrous alcohol when the equipment is working. If the fault occurs later or no longer occurs, it can be judged. Usually, it can only be eliminated by replacing with a new integrated circuit.