After discovering a capacitor failure, the core remedial measure is to replace the faulty capacitor. This is a process that requires careful handling, especially when dealing with high voltage or precision equipment.
The following are detailed remedial steps and precautions:
Safety first:
Complete power outage: Unplug the device from the power outlet, ensuring that there are no external power connections. If it is a battery powered device, remove the battery.
Internal discharge: There may be charges stored on the circuit board, especially large capacity capacitors (such as power filter capacitors). Before touching the circuit board, it is necessary to safely discharge the high-voltage points (especially the two ends of the large capacitor).
Method: Use a resistor with sufficient rated power (such as 1-5 watts) and moderate resistance (such as 1k Ω -10k Ω), and touch the two pins (or pads) of the capacitor on both ends of the resistor for a few seconds. Never short-circuit the pins directly with metal wires (such as screwdrivers)! Although this can discharge quickly, it can generate strong sparks that may damage capacitors, circuit boards, or components, and even harm the operator.
Anti static measures: When handling circuit boards, wear an anti-static wristband and and connect it to a reliable grounding point, or at least touch a grounded metal object (such as unpainted heating pipes or equipment cases) before work to release static electricity. Use anti-static pads.
Identify failed capacitors:
Visual inspection is the most common method:
Top bulge/protrusion: Most commonly seen in aluminum electrolytic capacitors, top explosion-proof valves (usually with K-shaped, cross shaped, or trident scratches) bulge or even rupture due to the generation of gas inside.
Bottom swelling/leakage: Electrolyte may seep out from the bottom rubber plug, causing the bottom of the capacitor to bulge or leaving brown, viscous, or crystalline residue on the circuit board (corrosive!).
Shell rupture/explosion: may occur in the event of severe failure.
Corrosion/discoloration of pins: Long term leakage or humid environment can cause severe corrosion of pins.
Attention: Some capacitor failures (such as decreased capacity, increased ESR) may not show significant visual changes and require the use of tools for inspection (such as multimeter capacitance range, ESR meter, LCR bridge).
Choose a suitable replacement capacitor:
The key parameters must match:
Capacitance value: must be the same as the original capacitance (unit: Farad F, commonly used microfarads µ F, nanofarads nF, picofarads pF). Allow for tolerances (such as ± 5%, ± 10%, ± 20%), but try to choose the same or better tolerance as the original.
Rated voltage: It must be equal to or higher than the rated voltage of the original capacitor. Absolutely not lower than! Otherwise, the new capacitor will quickly fail again or even burst. When space and budget allow, choosing a higher withstand voltage value is usually more reliable, but too high may affect volume and ESR.
Type: Try to use capacitors of the same type (such as aluminum electrolysis, tantalum electrolysis, ceramics, thin films). The characteristics of different types of capacitors vary greatly and cannot be interchanged arbitrarily. For example, tantalum capacitors cannot be directly replaced with aluminum electrolytic capacitors (unless circuit design allows and parameters are strictly matched), as tantalum capacitors are more sensitive to surge currents and back voltages.
Important feature considerations:
Temperature range: Especially for devices with high working environment temperatures (such as power supplies and amplifiers), choose the same or higher rated temperature as the original capacitor (such as 105 ° C being more heat-resistant than 85 ° C).
Equivalent series resistance: For high-frequency or high current applications (such as switching power supply output filtering), low ESR capacitors are necessary. A capacitor with an ESR value equivalent to or lower than the original capacitor should be selected. Specialized "low ESR" electrolytic capacitors or solid-state capacitors are commonly used in such situations.
Lifespan: The lifespan of electrolytic capacitors working in high-temperature environments is an important indicator (such as 2000 hours @ 105 ° C). Choosing capacitors with longer lifespan (such as 5000 hours @ 105 ° C) can improve reliability.
Size/Packaging: The diameter, height, and pin spacing must be compatible with the original capacitor to ensure installation on the circuit board. The size code of the surface mount capacitor must match.
Brand and Quality: Choose reputable brands such as Nichicon, Rubycon, Panasonic, Chemi Con, Vishay, TDK, Murata, etc. Avoid using cheap capacitors from unknown sources.
Remove the failed capacitor:
Tools: Use a suitable soldering iron (recommended constant temperature soldering iron) and a tin absorber/tape. For multi pin or surface mount capacitors, a hot air gun may be required.
Through hole capacitance:
One pin solder joint of the heating capacitor, wait for the solder to melt, and use a tin absorber to remove the solder.
Gently lift the pin to detach it from the solder hole.
Process another pin using the same method. If the capacitor is loose, you can carefully remove the entire capacitor.
Cleaning solder holes: Ensure that the solder holes are unobstructed and free from residual solder blockages.
Surface mount capacitor:
Soldering iron method (suitable for a small number of pins): Use a soldering iron to heat the solder pads at both ends simultaneously, or use a soldering iron to quickly alternate heating the solder pads at both ends, while gently picking up the capacitor with tweezers.
Hot air gun method (more commonly used and safer): Set the appropriate air volume and temperature (to avoid damaging surrounding components due to excessive heat), evenly heat the solder pads at both ends of the capacitor, and remove the capacitor with tweezers after the solder melts.
Cleaning solder pads: After removing the capacitor, use a soldering tape or iron with a soldering tool to clean the remaining old solder on the solder pads, making them flat and shiny. If the original capacitor leaks and corrodes the solder pad, it needs to be carefully cleaned with alcohol (isopropanol) and a cotton swab, and if necessary, gently sanded with fine sandpaper to remove the oxide layer.
Install new capacitor:
Polarity! Polarity! Polarity! Electrolytic capacitors (aluminum electrolysis, tantalum electrolysis) are divided into positive and negative poles, and surface mount tantalum capacitors are usually marked (with a horizontal line or a corner marker indicating the positive pole). The installation direction must be absolutely correct! Reverse connection can cause rapid failure, heating, and even explosion of capacitors. Install according to the markings on the original capacitor (electrolytic capacitors usually have arrows or ribbon markings on the negative pole) and the silk screen on the circuit board (usually marked with a "+" sign or shaded area indicating positive or negative pole). Confirm polarity repeatedly before welding!
Through hole capacitor: Insert the pins into the correct solder holes to ensure that the capacitor body is as close to the circuit board as possible (unless there are design requirements for suspension). First, weld one pin to fix it, adjust the position and direction, and then weld the other pin.
Surface mount capacitor: Use tweezers to align the capacitor with the solder pad (pay attention to polarity), first place a small amount of solder on one end of the solder pad to fix the position, then solder the other end, and finally turn back to solder the first end to ensure a firm and smooth soldering. Avoid prolonged heating time.
Welding technique: Use appropriate soldering wire (including rosin core). Keep the soldering iron tip clean. Heat the solder pads and pins to melt the solder and naturally distribute it to form smooth conical solder joints. Avoid virtual soldering (solder not well integrated with pads/pins) and cold soldering (rough and dull solder joints). Avoid short circuits caused by excessive soldering.
Inspection and testing after replacement:
Visual inspection: Confirm again that the polarity installation of all new capacitors is correct and error free. Check whether the solder joints are bright, round, without virtual soldering, and without short circuits (solder slag connects adjacent pads or wires).
Cleaning: Clean the welding area with alcohol (isopropanol) and a dust-free cloth or cotton swab to remove any residual rosin and possible soldering flux.
Functional testing (conducted with caution):
If possible, conduct a preliminary power on test without installing critical components (such as CPU, memory) or using a current limiting power supply to observe for any abnormalities (smoking, odors, abnormal sounds).
Use a multimeter to measure the voltage at key points (such as power output) and see if it returns to normal.
Gradually restore device configuration and conduct more comprehensive functional testing.
Important supplement:
Root cause investigation: Replacing capacitors is only a temporary solution. It is very important to consider why capacitors fail to prevent new capacitors from quickly being damaged again:
Natural aging: Electrolytic capacitors have limited lifespan, especially at high temperatures.
Overvoltage: Unstable power supply voltage or surge.
Overheating: Poor heat dissipation of the device, capacitors close to the heat source.
Overcurrent/Excessive Ripple Current: Circuit design issues or abnormal load.
Reverse voltage: reversed polarity or circuit design error.
Manufacturing defect: The original capacitor itself has poor quality.
If there is suspicion of external factors (overvoltage, overheating, etc.), it is necessary to solve these problems while replacing the capacitor (such as improving heat dissipation, checking the power supply).
Professional assistance: If you are unfamiliar with electronic maintenance, have high-value equipment, or involve high voltage or complex circuits, it is strongly recommended to seek the help of professional maintenance personnel. Incorrect operation may lead to further damage to the equipment and even personal danger.
Summary: The main remedy for capacitor failure is to replace the failed capacitor safely and correctly. The key lies in safe operation, precise identification of failed components, strict matching of replacement parameters (especially capacity, voltage, type, polarity), high-quality welding, and root cause investigation after replacement.