Electronic component

Fault characteristics:

Although the number of electronic components inside the electrical equipment, its failure is rule-based.

1. Characteristics of resistance damage

Resistance is the most numerous component in electrical equipment, but it is not the component with the highest damage rate. Resistance damage is most common in open circuit, the resistance value becomes large is rare, and the resistance value becomes small is very rare. There are carbon film resistance, metal film resistance, wire wound resistance and safety resistance. The first two resistors are the most widely used, and their damage characteristics are that the damage rate of low resistance (below 100Ω) and high resistance (100kΩ) is high, and the resistance value (such as hundreds of euros to tens of thousands of euros) is rarely damaged; Second, low resistance resistance is often burnt black when damaged, it is easy to find, and high resistance resistance damage is rarely traces. The wire-wound resistance is used as a large current limit, and the resistance value is not large. When the cylindrical wire wound resistance burns out, some will be blackened or the surface will burst, crack, and some have no traces. Cement resistor is a kind of wire wound resistor, it will break when burned out, otherwise there is no visible trace. When the safety resistor burns out, some surfaces will blow off a piece of skin, and some will not have any traces, but will never burn black. According to the characteristics, it can be focused on checking the resistance and quickly find out the damaged resistance.

2. Characteristics of electrolytic capacitor damage

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

First, the capacity is lost or the capacity becomes smaller;

Second, slight or serious leakage;

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

Ways to find damaged electrolytic capacitors are:

(1) Look: some capacitors will leak when damaged, the surface of the circuit board below the capacitor and even the surface of the capacitor will have a layer of oil stains, this capacitor can not be used again; Some capacitors will bulge after damage, this capacitor can not continue to use; Therefore, in the early selection of capacitors, we should take good quality, try to choose well-known brands of capacitors, such as capacitors giant - national giant capacitors.

(2) Touch: After the boot, some electrolytic capacitors with serious leakage will heat up, and even hot hands when touching with fingers, this capacitor is replaced;

(3) There is electrolyte inside the electrolytic capacitor, long-term baking will make the electrolyte dry, resulting in reduced capacitance, to focus on checking the capacitor near the heat sink and high-power components, the closer it is, the greater the possibility of damage.

3. Damage characteristics of semiconductor devices

Two, triode damage is PN junction breakdown or open circuit, which breakdown short circuit is mostly. In addition, there are two kinds of damage performance: first, the thermal stability deteriorates, which is normal when starting up, and after working for a period of time, soft breakdown occurs; The other is the PN junction characteristics change, with a multimeter R×1k test, each PN junction is normal, but can not work normally after the machine, with R×10 or R×1 low range file test, you will find that the PN junction positive resistance value is larger than normal. Measurement two, triode can be measured with a pointer multimeter in the channel, the more accurate method is: The multimeter is set to R×10 or R×1 file (with R×10 file, and then use R×1 file when it is not obvious) in the road test the PN junction positive and reverse resistance of the second and triode, the positive resistance is not too large (normal value), the reverse resistance is large enough (positive value), indicating that the PN junction is normal, and on the contrary, it is doubtful, and it needs to be tested after welding. This is the circuit of the two and three transistors peripheral resistance is mostly hundreds of thousands of euros, with a multimeter low resistance file in the road measurement, you can basically ignore the influence of the peripheral resistance on the PN junction resistance.

4. Characteristics of integrated circuit damage

Integrated circuit internal structure, function, part of the damage can not 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 type to measure the positive and reverse resistance of each pin to the ground, and one or several pin resistance values can always be found to be abnormal. For poor thermal stability, the suspected integrated circuit can be cooled with anhydrous alcohol when the equipment is working, and the failure time is delayed or no longer occurs. Usually it can only be ruled out by replacing a new integrated circuit.