It is often seen that many beginners are tossing on the resistance while repairing the circuit, and it is dismantled and welded. In fact, it has been repaired a lot. As long as you understand the damage characteristics of the resistance, you don’t have to spend much time.

Resistance is the most numerous component in electrical equipment, but it is not the component with the highest damage rate. Open circuit is the most common type of resistance damage. It is rare that the resistance value becomes larger, and the resistance value becomes smaller. Common ones include carbon film resistors, metal film resistors, wire wound resistors and insurance resistors.

The first two types of resistors are the most widely used. One of the characteristics of their damage is that the damage rate of low resistance (below 100Ω) and high resistance (above 100kΩ) is high, and the middle resistance value (such as hundreds of ohms to tens of kiloohms) Very little damage; 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.

Wirewound resistors are generally 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 resistors are a type of wire wound resistors, which may break when burned out, otherwise there will be no visible traces. When the fuse resistor burns 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 above characteristics, you can focus on checking the resistance and quickly find the damaged resistance.

According to the characteristics listed above, we can first observe whether the low-resistance resistors on the circuit board have burnt black marks, and then according to the characteristics that most of the resistors are open or the resistance becomes larger and the high-resistance resistors are easily damaged. We can use a multimeter to directly measure the resistance at both ends of the high-resistance resistor on the circuit board. If the measured resistance is greater than the nominal resistance, the resistance must be damaged (note that the resistance is stable before the display In conclusion, because there may be parallel capacitive elements in the circuit, there is a charge and discharge process), if the measured resistance is smaller than the nominal resistance, it is generally ignored. In this way, every resistance on the circuit board is measured again, and even if one thousand is “wrongly killed”, one will not be missed.