I often see many beginners tossing on the resistor when overhauling the circuit, and it is dismantling and welding, in fact, it is repaired a lot, as long as you understand the damage characteristics of the resistor, you don't have to bother.
Resistors are the most abundant components in electrical equipment, but they are not the ones with the highest damage rate. Resistance damage is most common in open circuits, and it is rare for the resistance to become larger, and it is very rare for the resistance to become smaller. There are several common types of carbon film resistors, metal film resistors, wirewound resistors and fuse resistors. The first two types of resistors are the most widely used, and their damage characteristics are that the damage rate of low resistance (below 100Ω) and high resistance (above 100kΩ) is higher, and the intermediate resistance (such as hundreds of ohms to tens of thousands of ohms) is rarely damaged; The second is that when the low-resistance resistance is damaged, it is often scorched and blackened, which is easy to find, while the high-resistance resistance is damaged and there are few traces. Wirewound resistors are generally used as high-current limiting, and the resistance value is not large. When the cylindrical wire winding resistor burns out, some will be blackened or burst on the surface, cracks, and some have no traces. Cement resistance is a type of wirewound resistor, which may crack when burned out, otherwise there is no visible trace. When the fuse resistor burns out, some surfaces will blow off a piece of skin, and some will not have any traces, but they will never burn and blacken. Based on the above characteristics, you can focus on the resistance when checking it, and quickly find out the damaged resistance.
According to the characteristics listed above, we can first observe whether the low resistance resistance on the circuit board has blackened traces, and then according to the characteristics of the vast majority of open circuits or resistance values become larger when the resistance is damaged and the high resistance resistance is easy to be damaged, we can use a multimeter to directly measure the resistance value at both ends of the high resistance resistance on the circuit board, if the measured resistance value is larger than the nominal resistance value, the resistance must be damaged (pay attention to the equal resistance value before drawing conclusions, because there may be parallel capacitive components in the circuit, there is a charging and discharging process), If the measured resistance is smaller than the nominal resistance, it is generally ignored. In this way, every resistor on the circuit board is measured, and even if it is "mistakenly killed" by a thousand, it will not let go of one.
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