Just as everything is born, electronic components also have a lifespan. The lifespan of an electronic component depends not only on its structure and properties, but also on its operating environment and its function within a circuit.
When winter is approaching, a sudden cold snap occurs. Some people with weaker constitutions cannot withstand the changes in temperature and catch a cold or fever, while those with strong constitutions have better resistance and do not get sick. This shows that illness is related to one's physical condition.
Even within circuits, there are varying degrees of strength. The following is a ranking of the resistance capabilities of electronic components:
Resistors, inductors, capacitors, and semiconductor devices (including diodes, transistors, MOSFETs, and integrated circuits) – in other words, under the same operating conditions, semiconductor devices have the highest probability of failure.
Therefore, when locating faulty components, we should prioritize checking diodes, transistors, MOSFETs, integrated circuits, etc. Generally, semiconductor devices are damaged by breakdown. When using a multimeter in diode beep mode, the resistance of any two pins of these devices should be at least 500 ohms at the PN junction. If there is a beep, it is probably broken. You can remove it and test it again to confirm.
We all know that the nail that sticks out gets hammered down first, and a leader's bodyguards must be prepared to sacrifice themselves at any time. This shows that the job position determines the level of danger.
In circuits, components operating under high voltage, high current, and high power conditions undoubtedly bear greater pressure and are more likely to be damaged. At the same time, they are also key and functional components of the circuit.
Any component that generates a large current will generate a large amount of heat (Joule's law—heat is proportional to the square of the current). Therefore, any component with a heat sink is a vulnerable component. High-power resistors are also vulnerable components. How can you tell if a resistor is high-power? It has nothing to do with its resistance value, only with its size; the larger the size, the higher the power.
In a circuit, fuses and fusible resistors are the least reliable components. Firstly, because they have a low melting point and are easy to break, and secondly, because they are the first to break when others break down.
Components can fail in various ways, including overvoltage damage, overcurrent damage, and mechanical damage. Overvoltage damage can occur, for example, from a lightning strike that can break down a bridge rectifier diode. Overcurrent damage can occur, for example, from thermal breakdown of the horizontal output transistor in a monitor.
Similarly, there are various ways to die. Overvoltage damage is like decapitation; the head is off, the person is dead, but the body remains intact. Components damaged by overvoltage show no obvious external changes, only that their parameters have completely altered. Overcurrent damage is like being brutally beaten to death; initially, one can withstand it, but it gradually becomes unbearable until death, when the component is covered in wounds and a bloody mess. Components damaged by overcurrent have very high surface temperatures, showing obvious changes such as cracks, discoloration, and small pits. In severe cases, the circuit board around the component turns yellow or black.
When common electronic components appear normal on the outside, a digital multimeter can be used to perform some simple tests.
Resistance: This is very simple, just test if the resistance value is correct.
Diode: Use a digital multimeter to test the voltage drop across the PN junction and compare it with a known good diode of the same type.
Transistors: Whether it is an N-type or P-type transistor, you can use a digital multimeter to measure and test whether the two PN junctions are normal.
Field-effect transistor (FET): Test whether the PN junction of the body diode of the FET is normal, and test whether there is a short circuit between GD and GS.
Capacitor: Non-polarized capacitor, short circuit or desoldering, severe leakage or resistive effect.
The practical characteristics of electrolytic capacitors are: breakdown and short circuit, increased leakage current, reduced capacitance, or open circuit.
Inductor: Its effective characteristics are open circuit and desoldering.
Chips: Integrated circuits have complex internal structures and many functions; damage to any part will prevent them from functioning properly. There are two types of integrated circuit damage: complete failure and poor thermal stability. In the case of complete failure, the circuit can be removed and its forward and reverse resistance to ground measured against a normal integrated circuit of the same model. This will usually reveal one or more pins with abnormal resistance values.
For components with poor thermal stability, the suspected integrated circuit can be cooled with anhydrous alcohol while the equipment is running. If the failure is delayed or ceases, the problem can be identified. Usually, replacing the integrated circuit is the only way to resolve the issue.
Whether the fault is caused by natural wear and tear or by human error, it can generally be classified into three types: open circuit, damaged electronic components, and software fault.
Open circuits, such as broken wires, disconnected connectors, or poor contact, are generally easy to troubleshoot. However, damage to electronic components (aside from obvious burns or overheating) is often difficult for observers to detect. In many cases, instruments are required for diagnosis. Therefore, it is essential for technicians to understand the characteristics of various components, which is crucial for troubleshooting circuit faults and improving efficiency.
