What a capacitor test tells you

A capacitor is a component that stores electrical charge temporarily. When it fails, it can cause a device to stop working or behave erratically. A multimeter — the handheld meter with a dial or digital display — can tell you whether a capacitor is holding a charge, leaking, or dead. The test takes about two minutes per capacitor and requires no special tools beyond the meter itself.

The goal is to see whether the capacitor charges up when you explore voltage to it, then holds that charge. A working capacitor will show a rising resistance reading that stabilizes. A failed capacitor will show no change, or will discharge when ready. This test works for most common capacitors found in household devices, though some specialized types require different methods.

Key Takeaways

  • Always unplug the device and discharge the capacitor by touching a screwdriver across its leads before you touch it with the meter.
  • Set your multimeter to the resistance setting (ohms), not voltage, to test whether a capacitor charges and holds a charge.
  • A working capacitor will show the resistance climbing from zero toward infinity as you hold the probes in place, then stay high.
  • A capacitor that shows zero resistance, stays at zero, or drops back to zero when ready is likely failed and should be replaced.
  • Some capacitors are too large or specialized for a multimeter test; if the reading is unclear, physical inspection for bulging or leaking is often more reliable.

Safety first: discharge the capacitor

Before you touch a capacitor with anything — your hands, the meter, a screwdriver — you must discharge it. A charged capacitor can deliver a painful shock even after the device is unplugged. The larger the capacitor, the more dangerous the stored charge.

Unplug the device completely from the wall outlet. Wait at least 30 seconds. Then take an insulated screwdriver (one with a plastic handle) and touch the metal tip across both leads of the capacitor at the same time. You may see a small spark or hear a pop — that is the capacitor releasing its charge, and it is normal. Do this once or twice to be certain the capacitor is fully discharged. Now it is safe to handle.

Set the multimeter to resistance mode

Turn the dial on your multimeter to the resistance setting. This is marked with the Greek letter omega (Ω) or the word "Ohms". Most meters have several resistance ranges — 200, 2000, 20,000, and so on. Start with the 20,000 ohm range (often labeled 20K) for small capacitors, or the 200,000 ohm range (200K) for larger ones. If you are unsure, start with 20K.

Do not use the voltage setting. Voltage mode will not charge the capacitor, so you will not see the behavior that tells you whether it is working. Resistance mode applies a small voltage from the meter's internal battery, which is what you need to observe the capacitor's response.

Touch the probes to the capacitor leads

A capacitor has two leads — the metal pins or wires sticking out from the component. One is marked positive (usually longer, or marked with a stripe or plus sign) and one is negative. It does not matter which probe touches which lead for this test, because you are measuring the capacitor's ability to charge, not its polarity.

Press the red probe to one lead and the black probe to the other. Hold them firmly in place. Watch the meter display as you do this. The needle or digital readout should move when ready.

Read the resistance climb and fall

When you first touch the probes to a working capacitor, the resistance reading will jump from zero and climb steadily toward infinity (the highest number on the scale, or "OL" on a digital meter, which stands for "over limit"). This climb happens because the capacitor is charging up through the meter's internal battery. The climb should take one to three seconds.

After the reading reaches the top, it should stay there or drop very slowly. This means the capacitor is holding the charge. Now remove the probes and touch them again. The same climb should happen again. If it does, the capacitor is working.

A capacitor that fails the test will show one of these signs: the resistance stays at zero and never climbs, the reading climbs partway and then drops back to zero while you are still holding the probes in place, or the reading jumps to infinity when ready and stays there without climbing. Any of these patterns means the capacitor is likely failed.

What to do with the results

If the capacitor passed the test — it climbed and held — you have ruled out a failed capacitor as the cause of the device problem. The issue is elsewhere. If the capacitor failed the test, it should be replaced. Note the capacitor's value (measured in microfarads, marked as µF or MFD on the component) and its voltage rating before you remove it, so you can buy an exact replacement.

Some capacitors are too large to test reliably with a multimeter. Electrolytic capacitors larger than about 100 microfarads may show a slow climb that never reaches the top, or may not respond clearly. In these cases, physical inspection is more useful: look for a bulging top, a split casing, or dried or leaked electrolyte around the base. Any of these signs means the capacitor has failed.

When a multimeter test is not enough

A multimeter test tells you whether a capacitor is completely dead or shorted, but it does not measure the capacitor's actual capacitance value. A capacitor can pass the climb-and-hold test but still be degraded — storing less charge than it should. If a device is behaving oddly and the capacitor passes the multimeter test, the capacitor might still be the problem.

Some devices use film capacitors or other types that do not respond clearly to a multimeter test. If you are testing a capacitor in a power supply, audio amplifier, or other high-voltage circuit, a multimeter test may not be safe or reliable. In these cases, replacement based on physical inspection or device symptoms is often the better choice.

Frequently Asked Questions

What does it mean if the resistance just stays at zero?

A capacitor that shows zero resistance and never climbs is shorted internally — the two sides are touching electrically when they should not. This capacitor is failed and must be replaced. It will not charge or hold any charge.

Can I test a capacitor while it is still soldered to the circuit board?

Not reliably. The rest of the circuit provides alternate paths for current, which interferes with the meter's reading. Desolder the capacitor first, or at least lift one lead so it is no longer connected to the board. Then test it in isolation.

Why does the reading climb slowly instead of jumping right to the top?

A slow climb is normal and usually means the capacitor is working. Very large capacitors charge slowly because they store a lot of charge. As long as the reading keeps climbing and eventually holds steady, the capacitor is functioning.

Is it safe to test a capacitor from a power supply or microwave?

Capacitors in power supplies and microwaves can store dangerous amounts of charge. Even after unplugging and waiting, they may hold a lethal voltage. If you are not experienced with high-voltage circuits, do not test these capacitors — replace them based on physical signs of failure instead.

What if the capacitor value is not printed on it?

Look at the circuit board or the device manual to find the capacitor's value. If you cannot find it, take a photo of the capacitor and the surrounding circuit to an electronics repair shop, or post the photo on an electronics forum. Someone can usually identify it from the board layout and nearby components.