Fault Characteristics & Maintenance of Capacitor In Circuit Board
The failure caused by capacitor damage is the highest in electronic equipment, especially the damage of electrolytic capacitors is the most common.
And capacitor damage is manifested as:
1. Smaller Capacity
2. Fully Lost Capacity
3. Leakage
4. Short Circuit
Since capacitors play different roles in the circuit, the faults caused by them also have their own characteristics.
In industrial control circuit boards, digital circuits account for the vast majority, capacitors are mostly used for power supply filtering, and certain 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 well filtered, and the circuit is logically confused due to unstable voltage, which is manifested as good or bad when the machine is working or open. If the capacitor is connected between the positive and negative poles of the power supply of the digital circuit, the fault is the same as above.
This is especially evident on computer motherboards. Many computers have been used for a few years and sometimes cannot be turned on, and sometimes can be turned on again. When opening the case, you can often see the phenomenon of bulging electrolytic capacitors. If you remove the capacitors, measure the capacity, then you’ll find those capacitors are much lower than the actual value.
The service life of the capacitor is directly related to the ambient temperature. The higher the ambient temperature, the shorter the service life of the capacitor. This rule applies not only to electrolytic capacitors, but also to other capacitors. Therefore, when looking for faulty capacitors, we 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 it is, the greater the possibility of damage.
Once repaired the power supply of an X-ray flaw detector, the user reported that there was smoke coming out of the power supply. After disassembling the case, it was found that there was a 1000uF/350V large capacitor with oil-like things flowing out. Remove a large amount of capacity. There are only dozens of uF, and it is also found that only this capacitor is closest to the heat sink of the rectifier bridge, and the others far away are intact and have normal capacity. In addition, there is a short circuit in the ceramic capacitor, and it is also found that the capacitor is relatively close to the heating component. Therefore, attention should be paid to the maintenance and search.
Some capacitors have serious leakage and even burn your hands when touched with your fingers. Such capacitors must be replaced.
In the case of good and bad faults during maintenance, except for the possibility of poor contact, most of the faults are generally caused by capacitor damage. Therefore, when encountering such failures, you can check the capacitors carefully. After replacing the capacitors, it is often surprising (of course, pay attention to the quality of the capacitors, and choose a better brand, such as ruby, black diamond, etc.)
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