The intuitive manifestations of capacitor failure are diverse, depending on the type of capacitor, its role in the circuit, and the severity of the failure. Here are some of the most common intuitive expressions that can be discovered through observation or simple operation:
1、 Physical appearance changes (most intuitive)
Bulge/Top protrusion (most common for electrolytic capacitors):
This is one of the most typical signs of aluminum electrolytic capacitor failure. The top of the capacitor, which was originally flat or had a marked explosion-proof groove, will visibly bulge, forming a "package" or causing the explosion-proof groove to crack and protrude.
Reason: The internal electrolyte is overheated and decomposes, producing gas, which increases the pressure and causes deformation of the outer shell.
Leakage/seepage:
Dark (usually brown or yellow) oil stains, paste like or crystalline substances can be seen seeping out from the bottom (pins), top (near the explosion-proof groove) or side of the capacitor body.
Reason: Sealing failure, internal electrolyte leakage. Electrolyte has corrosiveness and conductivity, which can further corrode circuit boards and components.
Shell cracking or damage:
The casing of ceramic capacitors, film capacitors, or electrolytic capacitors may have physical cracks, fractures, or even explosions.
Reasons: mechanical stress (such as falling or squeezing), thermal stress (drastic temperature changes), excessive internal pressure (electrolytic capacitors), voltage breakdown, etc.
Discoloration/burnt marks:
The capacitor body and the circuit board area near the pins may show signs of yellowing, blackening, or even carbonization.
Reason: Severe overvoltage and overcurrent caused internal breakdown and short circuit of the capacitor, resulting in high temperature burning.
2、 Functional abnormalities (intuitive representation at the device level)
The device cannot start or has difficulty booting up:
The failure of the power filter capacitor (especially the main filter capacitor) can cause unstable power supply voltage, excessive ripple, and the device may not be able to start at all, or it may require multiple attempts to start (manifested as the fan turning and then stopping repeatedly after pressing the power button).
Unstable device operation, random restart or crash:
The decoupling/bypass capacitors of critical circuits (such as CPU power supply and memory power supply) fail to effectively filter out noise or provide instantaneous current, resulting in abnormal chip operation, manifested as system blue screen, crash, program crash, irregular restart, etc.
The failure of signal coupling capacitors may cause signal distortion or interruption, resulting in abnormal sound (audio circuit), abnormal image (video circuit), or control failure.
Performance degradation:
The decrease in capacitance or increase in ESR of the power filter capacitor leads to an increase in power ripple. Although the device may still function, it will exhibit:
Slow running: such as computer CPU frequency reduction.
Insufficient output power: such as distortion, breakage, or buzzing sound (AC sound) in the audio system; The brightness of the monitor is unstable or there are interference fringes; The motor is powerless.
Decreased sensitivity: such as weakened signal reception and increased noise on the radio.
Complete failure of specific functions:
If the failed capacitor is located in a critical position of a functional module (such as an audio output coupling capacitor, a bypass capacitor of a specific sensor), it may result in the complete loss of that function (such as silence, no image, or an interface not working).
3、 Other perceptible/observable phenomena
Abnormal fever:
Be careful when touching a suspicious capacitor with your hands (note: it must be done after the device is powered off and the large capacitor has been discharged! High voltage danger!). If you feel abnormally hot (much higher than the temperature of the surrounding components), it indicates that the capacitor may overheat due to increased internal losses (such as increased ESR) or slight short circuits.
(A more professional approach is to use an infrared thermometer)
Audible noise:
In rare cases of severe failure (usually electrolytic capacitors), a small "hissing" sound (continuous internal discharge or electrolyte boiling) or even a "bang" sound (capacitor explosion) may be heard inside the capacitor.
Measurement abnormality (requires tools):
Although not "intuitive", measuring with a multimeter is a commonly used method for quick verification:
Significant decrease in capacity: far below the nominal value.
Significant increase in ESR: much higher than normal (ESR table required).
Short circuit: Resistance close to 0 ohms (severe breakdown).
Open circuit: infinite resistance (internal leads disconnected or completely dried up).
Leakage current is large: (requires specific testing conditions).
Summarize key points
Electrolytic capacitors (especially aluminum electrolysis): It is easiest to visually determine failure from appearance (bulges, leakage) and equipment power issues (non startup, instability, AC noise).
Ceramic capacitors and thin film capacitors: The appearance of failure may not be obvious (small cracks), but more often manifests as abnormal circuit function (signal distortion, noise, control failure) or, in severe cases, burning or short circuiting. The piezoelectric effect of multi-layer ceramic capacitors sometimes produces audible noise (whistling) at specific frequencies.
Tantalum capacitors: When they fail, they are prone to short circuits or even catching fire, and there may be visible burnt marks on the appearance.
'Functional abnormalities' are a widely present manifestation, but need to be analyzed in conjunction with the location of the capacitor in the circuit.
Important Notice:
When inspecting and replacing capacitors, be sure to disconnect the power supply of the equipment and ensure that the large capacity capacitors have been completely discharged (short circuit the pins with an insulated screwdriver for a few seconds, but be careful of sparks) to prevent electric shock.
Electrolyte is corrosive and should be cleaned promptly after contact.
When a capacitor is found to have failed, especially those working at high temperatures, high voltages, or critical locations, it is best to check the same batch or adjacent capacitors of the same specification, as they may also be nearing the end of their lifespan.
For failed capacitors, direct replacement is the only reliable method, do not attempt to repair them.
By observing these intuitive manifestations, it is possible to quickly locate and eliminate many electronic device failures caused by capacitor failures.