In the daily maintenance of electricians, detecting the working condition of components is a basic skill. We often see many students tinkering with resistors while repairing circuits, dismantling and soldering them. In fact, as long as you understand the damage characteristics of resistors, you don't have to go through a lot of trouble. Next, Ouyou Electronics will explain to you the reasons and judgment methods for resistor damage.

Reasons and judgment methods for resistance damage:

Resistors are the most numerous components in electrical equipment, but they are not the components with the highest damage rate. There are generally two types of reasons for resistance damage: external and internal.

There are many external reasons, such as excessive current causing burning or changes in resistance. The soldered circuit board undergoes deformation due to external forces, causing the resistor to break (especially in surface mount resistors). The heat generated cannot be discharged immediately, making it easy for the resistor to be damaged even when working in an overheated environment.

There are several common internal reasons: rough resistance quality, uneven material, resulting in changes in local resistance. The power selection is very close to the maximum power point, and when there is momentary interference, the resistor is damaged.

Resistance damage is most common in open circuits, with increasing resistance being rare and decreasing resistance being extremely rare. Common types include carbon film resistors, metal film resistors, wire wound resistors, and fuse resistors. The first two types of resistors are the most widely used, and their damage characteristics are high for low resistance values (below 100 Ω) and high resistance values (above 100k Ω), with very few damages for intermediate resistance values (such as several hundred ohms to tens of thousands of ohms); Secondly, when low resistance resistors are damaged, they often burn and turn black, which is easy to detect, while when high resistance resistors are damaged, there are few traces. Wire wound resistors are generally used for high current limiting and have a small resistance value. When cylindrical wire wound resistors are burned out, some may turn black or have surface peeling or cracks, while others may have no traces. Cement resistance is a type of wire wound resistance that may break when burned out, otherwise there will be no visible traces. When the fuse resistor burns out, some surfaces may explode with a piece of skin, while others may not have any trace, but they will never burn or turn black.

Based on the characteristics listed above, we can first observe whether there are traces of black burning on the low resistance resistor on the circuit board. Then, according to the fact that most resistors are open or have increased resistance when they are damaged, and high resistance resistors are easily damaged, we can use a multimeter to directly measure the resistance value at both ends of the high resistance resistor on the circuit board. If the measured resistance value is larger than the nominal resistance value, then the resistor will definitely be damaged (we should pay attention to waiting for the resistance value to stabilize before making a conclusion, because there may be parallel capacitor elements in the circuit, and there is a charging and discharging process). If the measured resistance value is smaller than the nominal resistance value, it is generally ignored. In this way, every resistor on the circuit board is measured once, even if a thousand are mistakenly killed, not a single one will be missed.