What a multimeter tells you about a capacitor
A multimeter is a handheld meter that measures electrical properties. When you use it to test a capacitor, you are checking whether the capacitor can still hold an electrical charge — the core job a capacitor does inside a device. A working capacitor will show a specific pattern on the meter's display; a failed one will not.
The test itself takes about two minutes and requires no special tools beyond the multimeter itself. You are looking for one of two things: either the meter will show a gradual change in resistance (which means the capacitor is charging and working), or it will show no change at all (which means it has failed). This matters because a dead capacitor often causes a device to stop working, even though everything else is fine.
Before you start, you must physically remove the capacitor from the circuit board or device. Testing a capacitor while it is still connected to power or to other components will give you a false reading and can damage the meter.
Key Takeaways
- You must disconnect the capacitor completely from the device before testing — a capacitor still connected to a circuit will not show its true condition.
- Set your multimeter to the resistance setting (ohms), not voltage, to see whether the capacitor can charge and discharge.
- A working capacitor will show the resistance climbing gradually from zero toward infinity as it charges; a failed capacitor will show no change.
- Larger capacitors take longer to charge, so give the meter 10 to 15 seconds to show a reading rather than expecting an when ready result.
- If the capacitor shows zero resistance and stays there, or shows infinite resistance from the start, the capacitor has failed and needs replacement.
Removing the capacitor safely
Before you touch anything, discharge any remaining charge in the capacitor. Even a capacitor that has failed can hold a small electrical charge that will hurt you or damage the meter. Touch both leads of the capacitor together with an insulated screwdriver or a wire to release this charge. You will see a small spark or hear a small pop — this is normal and means the discharge worked.
Once discharged, use a soldering iron or desoldering tool to remove the capacitor from the circuit board. If you have never soldered before, this is the step where you might ask someone with electronics experience to help, or take the device to a repair shop. Removing a capacitor without damaging the board requires heating the solder joints until they melt, then gently pulling the component free. If you pull too hard or heat the joint too long, you can lift the copper pad right off the board, making the repair impossible.
If the capacitor is in a straightforward plug-in device or a breadboard (a testing board used in electronics), you can straightforward pull it out by hand. Check the device manual or look at the board itself to see how the capacitor is mounted.
Setting up the multimeter
Turn on the multimeter and look at the dial or digital display. You need to find the resistance setting, which is marked with the Greek letter omega (Ω) or the word "ohms". This is not the same as the voltage setting (marked V) or the current setting (marked A). Turning the dial to the wrong setting will give you a useless reading.
If your multimeter has multiple resistance ranges (like 200Ω, 2000Ω, 20kΩ), start with the highest range available. This protects the meter from damage if the capacitor is in an unexpected state. You can always switch to a lower range if the needle or display does not move.
Once the meter is set to resistance, touch the two test leads together briefly to make sure the meter is working. The display should show zero or very close to zero. If it does not, the meter itself may have a problem, and you should not use it to test the capacitor.
Performing the test
Hold the two test leads of the multimeter against the two leads of the capacitor. It does not matter which lead touches which — capacitors work the same way in both directions. Press firmly so the metal makes good contact, but do not bend the capacitor's leads.
Watch the meter display. A working capacitor will show the resistance starting at zero and climbing slowly upward over the next 10 to 15 seconds. This climbing happens because the capacitor is charging through the meter's internal battery, and as it charges, it resists the flow of electricity more and more. This is the sign you are looking for — it means the capacitor can still store charge.
If the meter shows zero resistance and stays at zero no matter how long you wait, the capacitor has an internal short and has failed. If the meter shows infinite resistance (usually displayed as "1" on a digital meter, or the needle does not move on an analog meter) from the very first second, the capacitor has an open circuit and has also failed. Either way, the capacitor needs to be replaced.
What the results mean
A capacitor that climbs from zero to a high resistance reading is working. The exact number it reaches does not matter as much as the fact that it climbed at all. Different capacitors will reach different final values depending on their size and type, so you are not looking for a specific number — you are looking for the movement itself.
If you test the same capacitor a second time when ready after the first test, it will not climb again. This is normal. The capacitor is now fully charged, so it will not charge again until you discharge it. To test it a second time, touch the two leads together with an insulated tool to discharge it, wait a few seconds, and then test again.
A capacitor that shows zero resistance and does not climb, or shows infinite resistance from the start, has failed and should be replaced with a new capacitor of the same type and value. The value is printed on the capacitor's body — it looks like "10µF" or "100nF" — and you must match it exactly when you order a replacement.
When the test is unclear
Sometimes a capacitor will show a very slow climb that takes 30 seconds or more. This usually means the capacitor is very large (measured in farads) and is charging slowly through the meter's weak internal battery. This is still a working capacitor — it just needs more time. If you see any upward movement at all over a full minute, the capacitor is functional.
If the meter shows a reading that jumps around or flickers, the test leads may not be making good contact with the capacitor's leads. Clean the leads with a pencil eraser or fine sandpaper, dry them completely, and try again. Corrosion or oxidation on the leads can block the electrical connection and make the test unreliable.
Some digital multimeters have a dedicated capacitance setting (marked with a capacitor symbol) that measures capacitance directly in farads or microfarads. If your meter has this setting, you can use it instead of the resistance method. Set the meter to capacitance, touch the leads to the capacitor, and the meter will display the capacitor's value. If the reading is zero or blank, the capacitor has failed.
Reinstalling or replacing the capacitor
If the test showed the capacitor is working, you can solder it back into the device. If the test showed it has failed, order a replacement capacitor with the exact same value and type, then solder the new one in place of the old one. The value is printed on the capacitor's body — for example, "47µF 25V" means 47 microfarads at 25 volts. Match both numbers when you order.
When soldering the capacitor back in, heat the joint for no more than three seconds at a time. Capacitors are sensitive to heat, and too much heat can damage them. If you are not comfortable soldering, a repair shop can do this step for you.
Frequently Asked Questions
Can I test a capacitor while it is still connected to the circuit board?
No. A capacitor connected to other components will give a false reading because the meter is measuring the resistance of the entire circuit, not just the capacitor. You must desolder it first. The only exception is if you are using a dedicated capacitance meter setting, which some multimeters have — this setting can sometimes work on connected capacitors, but results are still unreliable.
What if the capacitor shows infinite resistance right away?
Infinite resistance from the start means the capacitor has an open circuit — one of its internal connections is broken. This capacitor has failed and needs replacement. Do not put it back in the device.
How long should I wait for the resistance to climb?
Wait at least 10 to 15 seconds. Very large capacitors may take 30 seconds or longer to show a noticeable climb. If you see any upward movement within a full minute, the capacitor is working. If nothing changes after a minute, it has failed.
Does it matter which test lead I touch to which capacitor lead?
No. Capacitors work the same way in both directions, so the order does not matter. Just make sure both leads of the multimeter are touching both leads of the capacitor at the same time.
What if I do not have a multimeter?
You can buy a basic digital multimeter for $10 to $20 at any hardware store or online retailer. If you only need to test one capacitor, a repair shop can test it for you for a small fee, usually $5 to $15.