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I'm troubleshooting a circuit board that has a dead short somewhere. I removed some capacitors which were shorted in circuit but the problem was elsewhere on the board.

When testing these 1500uf 2.5V capacitors they read as 1900uf in my capacitance tester. Could this be the result of age, a result of being within a faulty circuit for a prolonged period of time, or could they have come from the factory like this?

They don't have a brand written on them but were paired with Nichicon caps. The board itself was manufactured by MSI in the mid 2000s.

My other questions are speculative and not that important. My real question is that, assuming that these capacitors were installed like this from the factory, could such a difference in the rated capacitance create problems in the circuit?

I am a hobbyist with basic repair skills and have very little electronics experience and don't understand the consequences of what an out of spec capacitor can cause.

enter image description here

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    \$\begingroup\$ Capacitance depends on many factors: voltage, operating frequency etc. Electrolitic capacitors are well known for not having very precise capacitance. Their main advantage is favorable capacitance-to-price and high ESR which might help in damping, ie to suspend oscillations. They usually come with 20-30% tolerance on capacitance. Although capacitance mismatch might sometimes cause issues with control loop stability, that is not likely a problem here. How are you measuring short circuit? Note that if you measure short with multimeter on a capacitor, it would show short circuit! \$\endgroup\$
    – Marko
    Sep 20 at 20:44
  • \$\begingroup\$ Bear in mind that if you are investigating a circuit with semiconductors, the diode test setting on your multimeter may provide information that is more useful than the resistance setting. Also, a capacitor presents as a dead short when testing resistance as the capacitor starts being charged - try it with a spare capacitor to see how it behaves. More information in a YouTube video: Why I’m Always in Diode Mode - Let's make a test. \$\endgroup\$ Sep 20 at 21:03
  • \$\begingroup\$ Make sure you're not measuring a transformer connected to your measuring points. That may show as a short circuit. \$\endgroup\$
    – Rodo
    Sep 20 at 21:11
  • \$\begingroup\$ I am using the diode mode to test a short circuit, yes. \$\endgroup\$
    – Zhro
    Sep 20 at 21:40
  • \$\begingroup\$ You can use your bench top power supply to pump some voltage into your board, then use an infrared camera to see the short, which should heat up. You can also use high % alcohol, which should evaporate where the heat is being produced. You also may be able to feel it. Just respect the maximums -- don't put more than 12 volts into the 12 volt rail. If this is a motherboard, you probably have 3.3v, 5v, and may have a negative5 and/or negative12 volt rails. \$\endgroup\$ Sep 21 at 1:12
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Electrolytics such as that one are often +/-20%. In fact they may be more than +/- 20%. Depends on the manufacturer's specifications.

So the 1900 uF is on the high side but chances are that's not the source of your problem. This type of capacitor is usually used in a filtering circuit so having it higher than spec will not cause any problems.

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The question should rather be "what made the capacitor have larger than rated capacitance". Electrolytic capacitors have a thin oxide layer as dielectric. When they are not being used for a long time this layer shrinks, making for higher capacitance and lower maximum voltage. For power capacitors, this can be a problem: old music electronics have a reputation for exploding their power supply capacitors when put back to use after decades. So do the capacitors in electronic flashguns for photography (often the instructions tell you to power on the flash at least every few months) though the failure mode tends to be less dramatic but still rather loud and terminal.

If your capacitor is not used for power supply or power storage purposes, its voltage rating will likely not be taxed too tightly, so you can just use it and its voltage rating will likely return eventually with the capacitance going down. 25% over nominal capacity does not seem like extreme deterioration.

Power capacitors can usually be reformed gradually by putting them under increasing voltage a lot slower than normal use would.

The overcapacitance as such is not likely to make much of a problem in the circuit. The likely associated (temporary) deterioration of the voltage tolerance could.

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