What a bad capacitor looks like and why you need to test it
A capacitor that has failed will often show visible damage: a bulging or leaking top, a burnt smell, or corrosion around its leads. But a capacitor can fail electrically without looking broken, which is why a multimeter — a handheld meter that measures voltage, resistance, and continuity — is the fastest way to know whether a capacitor is actually bad or still working.
Capacitors store electrical charge and release it when a circuit needs it. When one fails, devices stop working, fans won't spin, or power supplies won't turn on. Testing takes about two minutes and costs nothing if you already own a multimeter. Most people find it easier than waiting for a replacement part to arrive or paying someone else to diagnose the problem.
The test itself is straightforward: you measure the capacitor's resistance in a specific way, and the meter tells you whether the part is holding a charge (good) or stuck (bad). This guide walks you through the exact steps, what the readings mean, and when you should stop and replace the part instead.
Key Takeaways
- Disconnect the capacitor from the circuit and discharge it by touching a screwdriver across its leads before testing, or you risk damaging the multimeter or yourself.
- Set the multimeter to the resistance setting (ohms), touch the probes to the capacitor's leads, and watch whether the reading climbs from zero toward infinity — that climb means the capacitor is good.
- A reading that stays at zero or stays stuck at a fixed number means the capacitor has failed and needs replacement.
- Larger capacitors (measured in microfarads) show a slower climb in resistance; smaller ones climb faster, so do not expect the same speed for every test.
- If the capacitor is still soldered to a circuit board, remove it first — testing it in place will give false readings because the rest of the circuit interferes with the test.
Prepare the capacitor and the multimeter
Before you touch the capacitor with the meter, you must discharge it — drain any electrical charge it is still holding. Even a small capacitor can store enough charge to damage a multimeter or give you a painful shock. The discharge takes five seconds and is the most important safety step.
Turn off and unplug the device. If the capacitor is soldered to a circuit board, desolder it and remove it completely. If it is already loose, hold it steady with one hand. Take an insulated screwdriver (one with a plastic handle) and touch the metal tip across both of the capacitor's leads at the same time. You may see a small spark — that is the charge leaving. Touch the leads again to be sure. If the capacitor is large, wait a few seconds between touches.
Set your multimeter to the resistance setting, marked with the Greek letter omega (Ω) or the word "ohms". If your meter has multiple resistance ranges (like 200Ω, 2kΩ, 20kΩ), start with the highest one. Do not use the continuity setting (usually marked with a sound-wave symbol) — that is for testing wires, not capacitors.
Touch the probes and read the resistance climb
Place one probe on each of the capacitor's leads. It does not matter which probe goes on which lead — capacitors work the same way in both directions. Watch the meter display. A good capacitor will show the resistance starting at zero (or very close to it) and then climbing steadily toward infinity, which the meter displays as "1" on the left side of the screen or as "OL" (overload).
This climb happens because the capacitor is charging up through the meter's internal battery. As it charges, it resists the flow of current more and more, so the resistance reading goes up. The climb usually takes between one and five seconds for most capacitors. Larger capacitors (ones rated in thousands of microfarads) climb slowly; smaller ones climb fast.
If the meter reaches infinity and stays there, the capacitor is good. Remove the probes and test is complete. If you want to test again, discharge the capacitor with the screwdriver and repeat — the climb will happen again.
Recognize a failed capacitor
A bad capacitor shows one of three readings: the meter stays at zero, the meter jumps to a fixed number and does not climb, or the meter shows infinity right away without any climb at all. Any of these means the capacitor has failed internally and cannot hold or release a charge properly.
If the reading stays at zero, the capacitor has shorted — the two sides of the capacitor are touching electrically when they should not be. If the reading jumps to a specific number and freezes there, the capacitor has an internal break or leak. If the meter shows infinity when ready with no climb, the capacitor is open — the internal connection is broken and no charge can flow at all.
In all three cases, the capacitor must be replaced. Write down the capacitor's voltage rating and microfarad rating (printed on its side), order a replacement with the same or higher voltage rating and the same microfarad rating, and install it in the same position.
What to do if the capacitor is still soldered in place
If you cannot easily remove the capacitor from the circuit board, you have two choices: desolder it first, or test it in place and accept that the reading may be wrong. Testing in place does not damage anything, but the rest of the circuit will interfere with the meter's reading, so you may get a false result.
If you decide to desolder, use a soldering iron and solder wick or a desoldering pump to remove the old solder from both leads. Once the leads are free, gently lift the capacitor away from the board. If you have never soldered before, this is the hardest part of the job — consider watching a video first or asking someone with soldering experience to help.
If you decide to test in place, discharge the capacitor first by touching a screwdriver across its leads on the board itself. Then touch the meter probes to the leads and watch for the resistance climb. If you see a climb, the capacitor is probably good. If you see zero or a stuck reading, the capacitor is probably bad — but to be certain, desolder it and test again away from the circuit.
Understand why the test works this way
A capacitor is two metal plates separated by an insulating material. When you explore voltage across it, one plate fills with electrons and the other plate empties, creating a charge. When you remove the voltage, the capacitor holds that charge until something drains it.
When you touch the multimeter probes to a discharged capacitor, the meter's internal battery tries to charge the capacitor through the probes. As the capacitor charges, it blocks the flow of current more and more — that is what resistance means. The meter measures this blocking and displays it as a climbing number. Once the capacitor is fully charged, it blocks all current, and the meter shows infinity.
If the capacitor is broken inside, it either lets current flow freely (shorted, so resistance stays at zero) or blocks it completely from the start (open, so resistance jumps to infinity with no climb). This is why the climb itself is the sign of a healthy capacitor — not just the final reading, but the journey to get there.
Common mistakes that give wrong readings
The most common mistake is testing a capacitor that is still charged. If you skip the discharge step, the capacitor's stored charge will interfere with the meter's reading and you may think a good capacitor is bad. Always discharge first, even if the capacitor looks dead.
The second mistake is testing a capacitor while it is still soldered to the circuit board. The rest of the circuit provides an alternate path for current, so the meter cannot see the capacitor's true resistance. If you get a confusing reading, remove the capacitor and test it alone.
The third mistake is using the wrong meter setting. The continuity setting will not work for this test — you must use the resistance (ohms) setting. If your meter has multiple resistance ranges, start with the highest one and work down if needed.
The fourth mistake is touching the metal parts of the probes with your fingers while testing. Your skin conducts electricity, so you become part of the circuit and change the reading. Hold the probes by their plastic handles only.
When to replace instead of test
If the capacitor is visibly damaged — bulging, leaking, burnt, or corroded — replace it without testing. The damage is proof enough that it has failed. Testing a damaged capacitor is safe, but it wastes time when you already know what to do.
If the device stopped working right after a power surge, lightning strike, or power outage, replace the capacitor without testing. Capacitors often fail during electrical stress, and the meter test takes longer than just ordering a replacement part. If the new capacitor fixes the problem, you were right. If it does not, you can test the old one then to rule it out.
If you are not confident desoldering the capacitor, and the device is not expensive, it may be faster and cheaper to take it to a repair shop than to learn soldering for this one repair. A technician can test and replace in minutes.
Frequently Asked Questions
Can I test a capacitor while it is plugged into power?
No. Always unplug the device first. Testing a live capacitor can damage the multimeter, injure you, or both. Even after unplugging, the capacitor may still hold a charge, which is why you must discharge it with a screwdriver before touching it with the meter.
Why does the resistance reading climb instead of staying the same?
The meter's internal battery is charging the capacitor through the probes. As the capacitor fills with charge, it resists the flow of current more and more, so the resistance reading climbs. Once fully charged, it blocks all current and the meter shows infinity. This climb is the sign of a healthy capacitor.
What if the meter shows a number but does not climb?
If the reading jumps to a specific number and stays frozen there, the capacitor has failed internally. It may have a short circuit or an internal break. Replace it. If the reading is zero and does not move, the capacitor is shorted and must be replaced.
Do I need to test both leads, or can I test one lead at a time?
You must touch both leads at the same time with the two probes. A capacitor stores charge between its two plates, so you need to complete a circuit through both leads for the meter to see the charge. Testing one lead alone will not work.
How long should I wait for the resistance to climb?
Most capacitors climb to infinity in one to five seconds. Larger capacitors (rated in thousands of microfarads) climb slowly, sometimes taking ten seconds or more. Smaller capacitors climb fast, sometimes in under a second. If nothing happens after ten seconds, the capacitor has probably failed.