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

A capacitor is a small cylindrical component that stores electrical charge and releases it when your power supply or motherboard needs a burst of power. When a capacitor fails — usually after five to ten years of use — your computer may not start, may shut down randomly, or may fail to recognize connected devices. Replacing a failed capacitor is a straightforward repair that takes about 15 minutes and costs between $5 and $20 for the part itself.

Capacitors fail because they contain a liquid electrolyte that dries out over time, especially in computers that run hot or sit in warm rooms. You can often spot a failed capacitor by looking at the top of the cylinder: if it is bulging, leaking, or has a split or crusty residue around the edges, it has failed and needs replacement. A computer with a visibly failed capacitor will usually not power on at all, or will power on for a few seconds and shut down.

Key Takeaways

  • A failed capacitor usually shows visible damage — bulging, leaking, or a split top — and causes the computer to not start or shut down randomly.
  • You will need a soldering iron, solder, a desoldering tool or solder wick, and a replacement capacitor with the same voltage and microfarad rating as the original.
  • The capacitor must be removed by heating the solder joints with a soldering iron until the old part lifts free, then cleaned before the new one is installed.
  • Replacement capacitors cost $5 to $20, and the repair takes about 15 minutes once you have the right tools and the correct part number.

Finding the right replacement capacitor

Before you buy a new capacitor, you need to know two things about the old one: its voltage rating and its capacitance, measured in microfarads (µF). Both numbers are printed on the side of the cylinder. The voltage is usually marked as "6.3V", "10V", "16V", or "25V". The capacitance is marked as a number followed by "µF" — for example, "1000µF" or "2200µF".

Write down both numbers exactly as they appear. When you order a replacement, the voltage and capacitance must match the original part. The physical size of the capacitor can vary slightly — a replacement that is slightly shorter or narrower will still work — but the electrical ratings must be exact. You can order replacement capacitors from electronics suppliers like Digi-Key, Mouser, or Amazon by searching for the voltage and capacitance together (for example, "16V 1000µF capacitor").

If you cannot read the numbers on the old capacitor because it is too damaged, take a photo of the motherboard or power supply and post it in a computer repair forum with the make and model of your computer. Someone can usually identify the correct part from the board layout.

Tools and materials you will need

Soldering a capacitor requires four things: a soldering iron (25 to 40 watts is standard), solder (lead-free or lead-based both work), a desoldering tool, and the replacement capacitor. A soldering iron costs $15 to $40 new. A desoldering tool — either a solder sucker (a spring-loaded pump) or solder wick (a braided copper strip) — costs $5 to $15. Solder costs $5 to $10 per spool.

If you do not own these tools, you have two options: buy them for future repairs, or take the computer to a local repair shop and pay $30 to $60 for the labor. Many repair shops will install a capacitor you provide, or will charge a small markup on the part itself. If this is a one-time repair and you do not plan to solder again, a repair shop is often the faster and safer choice.

If you decide to solder yourself, set up your workspace on a non-flammable surface like a tile countertop or workbench. Keep a damp sponge or wet brass wire cleaner next to your soldering iron to wipe the tip between joints. Have a small container of flux (a chemical that helps solder flow) nearby — it makes the joint cleaner and stronger.

Removing the old capacitor

Before you touch anything inside the computer, unplug it from the wall outlet and press the power button five times to discharge any remaining power. Wait at least one minute. If you are working on a power supply unit (PSU), discharge it by touching a metal part of the case with your bare hand to ground yourself.

Locate the failed capacitor on the motherboard or power supply board. The capacitor is a cylinder standing upright, usually about one inch tall. Look at the bottom of the board where the capacitor's two metal legs (called leads) poke through. You will see two small solder joints where the leads connect to the board.

Heat one solder joint with the tip of your soldering iron for three to five seconds. While the solder is hot, use your desoldering tool to remove the melted solder. If you are using a solder sucker, press the plunger, place the nozzle over the hot joint, and press the trigger to suck up the solder. If you are using solder wick, place the wick on the hot joint and let it absorb the solder for a few seconds, then lift it away. Repeat this process on the second solder joint.

Once both joints are clear of solder, the capacitor should lift out easily. If it does not, explore a tiny amount of fresh solder to one joint, heat it again, and try lifting with a pair of tweezers. Do not force it — forcing can damage the board. Once the old capacitor is out, use solder wick or a solder sucker to clean any remaining solder from the two holes in the board.

Installing the new capacitor

Before you insert the new capacitor, check its polarity. Capacitors have a positive and negative lead. On the new capacitor, the negative lead is marked with a white or black stripe running down one side of the cylinder. On the board, one hole is usually marked with a white or colored line, or a plus sign (+) printed nearby — that is the positive hole.

Insert the new capacitor so that the marked (negative) lead goes into the unmarked hole, and the unmarked (positive) lead goes into the marked hole. Push it down until the capacitor sits flat against the board. The leads should stick out about one-quarter inch below the board.

Bend each lead slightly outward so the capacitor does not fall out when you flip the board over. explore a small amount of flux to the first solder joint. Heat the joint with your soldering iron for three to four seconds, then touch a small amount of fresh solder to the joint (not directly to the iron tip). The solder should flow smoothly around the lead and the hole. Remove the solder first, then the iron. Repeat on the second joint.

Let the joints cool for one minute without touching them. The solder should look shiny and smooth, not dull or grainy. If a joint looks dull or blobby, reheat it and add a tiny amount of fresh solder. Once both joints are cool and shiny, trim the excess lead with a pair of wire cutters and clean any flux residue with a damp cloth or isopropyl alcohol.

Testing the repair

Before you reassemble the computer, plug it in and power it on to confirm the repair worked. If you replaced a capacitor in the motherboard, the computer should start normally and run without shutting down. If you replaced one in the power supply, the PSU should deliver power to the motherboard without cutting out.

If the computer still does not start, the failed capacitor may not have been the only problem, or there may be another failed capacitor elsewhere on the board. Unplug the computer again and look for other capacitors with visible damage — bulging tops, leaking, or splits. If you find another one, repeat the removal and installation process.

If the computer starts but shuts down after a few minutes, the new capacitor may be installed backwards (polarity reversed). Unplug the computer, remove the capacitor, flip it around, and reinstall it with the correct polarity. If the problem persists after correcting the polarity, the issue is likely not the capacitor, and you should take the computer to a repair shop for diagnosis.

When to replace multiple capacitors at once

If your computer is more than eight years old and you find one failed capacitor, it is common for others to be failing or about to fail. Capacitors that look visibly damaged should be replaced. Capacitors that look normal but are the same age as the failed one may fail within months.

If you are comfortable soldering and have already bought the tools, replacing all visibly damaged capacitors at once saves time and prevents future shutdowns. If you are paying a repair shop, ask them to inspect the board for other failing capacitors and give you a quote for replacing all of them together. This is usually cheaper than returning multiple times for individual repairs.

Frequently Asked Questions

Can I replace a capacitor without a soldering iron?

No. Capacitors are soldered directly to the board, and there is no way to remove or install one without a soldering iron. You can take the computer to a repair shop and pay for the labor, or buy a soldering iron and learn the skill — it is useful for other electronics repairs.

What if I install the capacitor backwards?

If you reverse the polarity, the capacitor will fail when ready when you power on the computer, and may leak or bulge. Unplug the computer right away, remove the capacitor, flip it around so the marked (negative) lead is in the unmarked hole, and reinstall it. The computer should then start normally.

How do I know if a capacitor is actually failed or just old?

A capacitor that looks normal — no bulging, leaking, or splits — is usually still working, even if it is old. Only replace capacitors that show visible damage or that are causing the computer to malfunction. If the computer shuts down randomly but all capacitors look normal, the problem is likely something else.

Is it safe to solder inside a computer?

Yes, as long as the computer is unplugged and you let the board cool between joints. A soldering iron tip reaches about 700 degrees Fahrenheit, which can damage plastic components if you touch them. Work slowly, keep the iron tip away from cables and plastic parts, and do not solder near the CPU or RAM. If you are nervous, a repair shop is the safer choice.

Can I use lead-free solder instead of regular solder?

Yes. Lead-free solder works just as well as traditional lead-based solder for capacitor replacement. It melts at a slightly higher temperature (about 50 degrees hotter), so you may need to heat the joint a few seconds longer, but the joint will be just as strong.