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Replacing bad capacitors


Computer motherboards and other electronic equipment like power supplies have electrolytic capacitors inside.
Bad capacitors are a big problem because they can make our computer stop from booting.
Sometimes we press the power button on the computer and the boot process does not always begin. If it only boots up once we power it off and on again, then it is time to open it and look inside in order to check visually the capacitors health.

damaged capacitors
Pentium IV motherboard with bad capacitors.
damaged capacitors
Bad capacitors stop our computer from booting.

Capacitor plague: the true history

Bad capacitors are really a plague. There are many bad capacitors in the market due to an incorrect electrolyte formula used in some factories. It is well known that industrial espionage is one of the sources for this failure.

Some Taiwanese electrolyte manufacturers used a stolen formula that was incomplete, this formula produced unstable capacitors.

bad capacitors macro
The top is damaged, but sometimes the bottom is also.

Dangers of capacitors

Visually we cannot say if a capacitor is charged or it is not. When touching the capacitors leads, be careful to not get shocked. More voltage rating means more danger.
A capacitor may also explode by the effects of excessive voltage.
Please take care.

Do not get burnt or shocked.

The tools

We will need some tools, they are not mandatory except for the iron.
There are many ways to remove the capacitors and solder the new ones, but this is our choice.

The iron

A very cheap iron for this job.

For this repair we will need an iron that must have a power of 60W to 80W, using a 25W iron will not become a successful operation. This is very important.

The mechanical solder pump

This tool is needed in order to remove the remaining solder when removing the capacitors. It's optional.

The needle

A sharp needle is useful to clean the motherboard holes, it must be a very hard and thin needle. It could be really helpful and will speed up the process.


Sometimes there is a white hemisphere in the board that indicates negative. On the capacitor a painted vertical stripe with the minus signal indicates negative.
White hemisphere is the place to solder the negative lead indicated by the capacitor strip.

Equivalent capacitors

Capacitance rating is measured in microfarads and the voltage rating is measured in volts.
When changing a capacitor we will always use the same capacitance rating. We can use the same voltage rating or higher.
For example, a 3300 microfarads and 6.3 volts can be replaced by a 3300 microfarads and 10 volts.
The voltage rating does not mean that the capacitor is charged like a battery to X microfarads, it means that if you charge it over X, then it will explode. So it is safer to use a higher volt range.
This is a nice video about capacitor replacement tutorial by Afrotechmods.

Where can we new capacitors?

Buy them online with very cheap shipping cost, buy them on your local electronics store or get it for free from another motherboard that is going to be trashed.

new capacitor
A classic capacitor found on a Pentium IV computer.
motherboard back new capacitors
All the new capacitors almost ready.

Changing bad capacitors

The procedure to change capacitors is:

  1. Disconnect the motherboard, even remove the lithium battery (CR2032) while working.
  2. Remove the CPU and the fan for working easily.
  3. Clean up all the dust.
  4. Take a picture or draw a schema of the capacitors to be changed.
  5. Indicate in that drawing the microfarads, voltage, negative lead and location of the capacitors to avoid errors.
  6. Fix the motherboard vertically, be sure that it does not move while working.
  7. Apply heat by using the iron in the two holes back in the motherboard.
  8. When hot enough, with the other hand get with your fingers the capacitor's top and move it slightly while pulling it away from the board.
  9. Once removed, suck the tin with the mechanical pump to leave the hole cleaned.
  10. Use the needle to drill across the board, so the new capacitor leads can pass through it.
  11. Insert the capacitor leads carefully looking for the right polarity and capacitor type.
  12. Solder the capacitor's leads in the back of the board.
  13. Repeat the operation for every bad capacitor.

capacitors good
The motherboard is ready as a new one.


Before our computer passes away, we must take a look at the motherboard. If the capacitors look wrong, it is time to change them, before it is too late. The cost of the materials is very low. It is a worth effort. Too many people buy a new computer when the problem is simply a bunch of bad capacitors.
We will keep our old mobo running!

September 2011.

Use main page comments for questions.

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