What a capacitor does and why you might need to replace one

A capacitor is a small electronic component that stores and releases electrical charge. In most devices, capacitors smooth out power delivery, filter noise from signals, or help circuits start up. When a capacitor fails — usually after years of use — the device may not power on, may shut down unexpectedly, or may produce no sound or video.

Replacing a capacitor is one of the most common repairs for older electronics: power supplies, monitors, amplifiers, and vintage computers. If you have a device that worked fine and then stopped, a failed capacitor is often the culprit. This guide covers the physical steps to remove and install a new one.

Key Takeaways

  • Capacitors are soldered to circuit boards, so you will need a soldering iron, solder, and a desoldering tool or solder wick to remove the old one.
  • Before you start, discharge the device completely by unplugging it and holding the power button, because capacitors can hold a dangerous electrical charge even when the device is off.
  • Match the new capacitor's voltage rating and microfarad (µF) value exactly to the old one — the markings are printed on the side of the component.
  • Solder the new capacitor in the same orientation as the old one: the longer lead goes to the positive side, marked with a plus sign or a stripe on the board.

Gather the tools and parts you will need

To install a capacitor, you need a soldering iron (25 to 40 watts is typical for circuit boards), solder (lead-free or lead-based, 60/40 or 63/37 tin-to-lead ratio), and a way to remove the old capacitor. A desoldering pump (also called a solder sucker) or solder wick (also called desoldering braid) both work — solder wick is often easier for beginners because you lay it on top of the solder joint and heat it, and the solder wicks up into the braid.

You will also need the replacement capacitor itself. Find the value printed on the old one: it will show a number followed by µF (microfarads) and a voltage rating, such as "10µF 50V" or "2200µF 16V". Order an exact match or a capacitor with the same µF value and a voltage rating equal to or higher than the original. Do not use a lower voltage rating.

Have a small screwdriver set, tweezers, and a magnifying glass or headlamp on hand. If the device has a large power supply capacitor, wear safety glasses — a failed capacitor can rupture and spray electrolyte.

Discharge the device and locate the capacitor

Unplug the device from the wall outlet. If it has a battery, remove it. Press and hold the power button for 10 to 15 seconds to drain any remaining charge from the capacitors. This step is critical: even a device that has been unplugged for days can hold enough charge to cause a painful shock or damage your soldering iron.

Open the device according to its design. Most electronics have screws on the back or underneath; remove them and set them aside in order so you know where each one came from. Locate the capacitor you need to replace. If you are not sure which component is the capacitor, look for a cylindrical or rectangular part with two leads (wires) sticking out of the bottom, or a flat component with markings on top. The value and voltage are printed on the side or top.

Take a photo of the capacitor and its orientation before you remove it. Note which lead is longer (positive) and which is shorter (negative), or look for a stripe on the component that marks the negative side.

Remove the old capacitor

Heat your soldering iron for two to three minutes. Touch the iron tip to one of the solder joints where the capacitor lead meets the circuit board. Hold it there for three to five seconds until the solder melts and turns shiny. If you are using a desoldering pump, press the plunger, place the nozzle over the joint, and trigger it to suck up the melted solder. If you are using solder wick, lay it on the joint and hold the iron tip against it until the solder wicks up into the braid, then remove both the wick and the iron.

Repeat this process on the second lead. Once both joints are clear, the capacitor should pull free. If it does not, gently wiggle it side to side while heating one joint. Do not yank it — you can tear the pad off the circuit board, which makes reinstalling a new component much harder.

Inspect the two holes where the capacitor was soldered. They should be clean and free of old solder. If solder is still blocking them, repeat the desoldering process on each hole.

Install the new capacitor

Insert the new capacitor into the same holes, making sure the longer lead (positive) goes into the hole marked with a plus sign or a stripe on the board. The shorter lead (negative) goes into the unmarked hole. If the leads are too long, you can trim them with wire cutters, but leave at least a quarter-inch of lead sticking out so you have something to solder.

Bend the leads slightly outward so the capacitor sits flat against the board and does not fall out when you flip the board over. Some people use a small piece of tape to hold the capacitor in place while soldering, but this is optional.

Heat the soldering iron again. Touch the tip to the lead and the pad at the same time, not to the lead alone. After two to three seconds, touch a small amount of solder to the joint — not to the iron tip. The solder should flow around the lead and pad, forming a shiny cone shape. Remove the solder first, then the iron. Repeat on the second lead.

Check your work and reassemble

Look at both solder joints. They should be shiny and smooth, forming a cone from the pad to the lead. A dull, grainy joint means the solder did not melt properly — reheat it and add a tiny bit more solder. A joint that looks like a blob or has too much solder can be cleaned up by heating it and using solder wick to remove the excess.

Let the board cool for a minute. Trim any excess lead with wire cutters if needed. Inspect the area around the capacitor to make sure you did not accidentally solder a nearby component or bridge two pads together with solder.

Close up the device, reinstall the battery if it has one, and plug it in. Power it on and see if it works. If the device still does not work, the capacitor may not have been the only failed part, or you may have accidentally damaged something during the repair.

Frequently Asked Questions

How do I know which end of the capacitor is positive?

The longer lead is positive. On some capacitors, the negative side also has a stripe or line printed on the component itself. Check your photo before you remove the old capacitor so you know the correct orientation.

What if I accidentally solder two pads together?

This is called a bridge. Heat the joint with your iron and use solder wick to remove the excess solder, or use a desoldering pump. If the bridge is between two leads of the same capacitor, it will not hurt anything. If it bridges to a nearby component, it can cause a short circuit and damage the board.

Can I use a different voltage rating if the exact one is not available?

Yes, but only if the new capacitor has a voltage rating equal to or higher than the original. A 10µF 50V capacitor can be replaced with a 10µF 63V or 10µF 100V capacitor. Never use a lower voltage rating — the capacitor will fail quickly and may rupture.

Do I need to match the brand of the capacitor?

No. Any capacitor with the same µF value and voltage rating will work. Some brands are more reliable than others, but for a repair, any standard capacitor from a reputable electronics supplier is fine.

What if the device still does not work after I replace the capacitor?

The capacitor may not have been the only failed part. Other components can fail at the same time, or the device may have a different problem altogether. If you are not comfortable troubleshooting further, a repair technician can test the board and identify other issues.