How to Replace capacitors!

Hello world! I’m Noah, and today, instead of something interesting, I’m going to give you an in-depth guide on how to replace capacitors. But first, a little story.

Almost exactly a year ago, my Uncle asked me to see if I could fix his computer. I took a look at it, and, thanks to the help of the Internet, concluded the problem to be blown capacitors (The main piece of evidence was all of the blown capacitors.) At that time, I didn’t even own a soldering iron, let alone know how to use one, so I wouldn’t be any help re-capping the motherboard. So I did as best I could, which was to get an IDE-to-usb enclosure, package everything up, and give my Uncle his brand-new harddrive-turned-thumbdrive. After that, I packed the rest of the computer away under a table somewhere and forgot all about it.

I remembered the computer a week ago and realized that I, now one year older, wiser, and more skilled, have the skills to re-cap this computer. Why not give it a go? So I put in an order on Mouser for the capacitors I needed, and soon after, got going. Working on this computer, I gained a lot of handy knowledge about the whole process of replacing capacitors, so I’ll break it down real nice and easy, beginning to end. It’s not very hard, so here goes!

1: Buy the capacitors

This isn’t super difficult. Just log on to your favorite parts supplier (I suggest Mouser or Digikey since they have such an awesome selection) and order the caps. Make sure you have the right capacity and voltage, but also, and I almost forgot to do this myself, REMEMBER TO ORDER THE SAME SIZE. I was halfway to the checkout screen when I realized that the caps I had were twice as wide as the ones on the motherboard. This would’ve caused serious problems had I not caught it, so make sure to do the same. A handy-dandy ruler will help you figure out the size of your caps. Most of the time, height is less important than width, since there’s often a ton of headroom, but try and get it as close as possible just in case.

2: Identify bad capacitors

Here’s a picture of several capacitors on the motherboard I was working on: Image

As you can see, 2 of them have dielectric leaking out, and the rest are bulging, so they’re probably not far behind. Basically, any capacitor that looks like the top is about to explode off of it needs to be replaced.

3: Preparing your capacitors 

A trick I learned about while researching is to snip the leads of your replacement capacitors to a much shorter length; they originally have way too much space between the tip of the legs and the beginning of the cap. Here’s what they should look like for maximum handiness:

ImageClip them to this length, or a bit longer. A lot longer if you’re putting it in a hard-to-reach place such as between other capacitors, as “aiming” is easier with longer legs. Clip one leg a bit shorter than the other for maximum handiness.

4: Remove old capacitor. 

    No picture here. Just apply your soldering iron to one pad on the underside of the motherboard, and push the cap lightly so that it “Leans” a bit away from the heated pad. The leg should slide out without too much effort. Do the same with the other pad while pulling the capacitor gently away, and you should find that it isn’t too hard. If it takes more force, apply said force liberally and without restraint (Don’t actually do this.)

5: Confirm Polarity

I went into this expecting to have to remember the polarity of each capacitor I removed, and make sure to place the new one in the same way, lest I reverse one and the computer explodes. Luckily, there are a couple ways to tell the polarity of the cap you’re putting in. Firstly, on the topside of the circuitboard, in the footprint of the original capacitor, there is a little arrow denoting where the positive leg goes. It looks like this: ImageSee how great that is? Now you don’t have to guess how to orient your capacitor. Easy!

Secondly, if you look closely, the solder-holes have a trick of their own which will tell you all you need to know. If you look at the above picture, you can see that the leg-holes (yes I know that’s not the official word for them) are different shapes. It turns out that this is the same throughout the board. The positive hole is square, and the negative is circular. This is a pretty good way to be sure you’re not screwing everything up.

6: Insert new capacitor.

This is it. The moment you’ve been waiting for. Do this. I believe in you. Position one leg into it’s hole. It probably won’t go through, since leftover solder loves to fill tiny holes. Place your iron on the other side of the hole, and as the solder melts, the leg should slide in. Slide it in a bit, then position the other leg and do the same thing. Once they’re both in, moving the whole thing flush to the board is no problem.

If it doesn’t look something like this, you are a failure:ImageNow comes the simple matter of applying some solder to the joints to make everything solid, and there you go! You’ve just replaced a capacitor! Now only 378 to go until your computer works!