PCB News - Fault characteristics and maintenance of circuit board capacitor damage

The faults caused by capacitor damage are the highest among PCB boards, and the damage of electrolytic capacitors is the most common among them.
The performance of capacitor damage is: a. The capacity becomes smaller; b. The capacity is completely lost; c. Leakage; d. Short circuit.

Capacitors play different roles in the circuit, and the faults they cause have their own characteristics. In industrial control PCB boards, digital circuits account for the vast majority, and capacitors are mostly used for power supply filtering, and less capacitors are used for signal coupling and oscillation circuits. If the electrolytic capacitor used in the switching power supply is damaged, the switching power supply may not vibrate, and there is no voltage output; or the output voltage is not filtered well, and the circuit is logically chaotic due to voltage instability. No matter the machine, if the capacitor is connected between the positive and negative poles of the power supply of the digital circuit, the failure will be the same as above. This is especially obvious on computer motherboards. Many computers sometimes fail to turn on after a few years, and sometimes they can be turned on. Open the case, you can often see the phenomenon of electrolytic capacitors bulging. If you remove the capacitors to measure the capacity, Found to be much lower than the actual value.

The lifetime of a capacitor is directly related to the ambient temperature. The higher the ambient temperature, the shorter the lifetime of the capacitor. This rule applies not only to electrolytic capacitors, but also to other capacitors. Therefore, when looking for faulty capacitors, you should focus on checking the capacitors that are close to the heat source, such as the capacitors next to the heat sink and high-power components. The closer you are to it, the greater the possibility of damage. I have repaired the power supply of an X-ray flaw detector. The user reported that smoke was coming out of the power supply. After disassembling the case, I found that there was a 1000uF/350V large capacitor with oily things flowing out. Removed a certain amount of capacity. It is only tens of uF, and it is found that only this capacitor is the closest to the heat sink of the rectifier bridge, and the others far away are intact and have normal capacity. In addition, there was a short circuit in the ceramic capacitor, and it was also found that the capacitor was relatively close to the heating component. Therefore, there should be some emphasis in the inspection and search.

Some capacitors have serious leakage current, and even burn your hands when touched with your fingers. This type of capacitor must be replaced.
In the case of ups and downs during maintenance, except for the possibility of poor contact, most of the failures are generally caused by capacitor damage. Therefore, when encountering such failures, you can focus on checking the capacitors. It is often surprising after replacing the capacitor (of course, pay attention to the quality of the capacitor).

The above is the introduction of the fault characteristics and maintenance of the circuit board capacitor damage. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.