Capacitor question

If you don't have money in the board I would go for it. Take out the caps. Clean the holes with de-solder and don't cut the legs of the new caps until you are finished soldering the new ons on. Remember caps are polarized. You need to get the pos+ and neg- in the right holes.

That would probably alter the overall capacitance, if the old ones are not removed. I read somewhere that you would need a high power soldering iron to do the job effectively, as lots of heat is required to melt the solder. Having a de-soldering pump would be handy too in this kind of bad cap replacement job.

That really would be more difficult than just completely desoldering the old cap, and replacing it with a new one.

You can pick up a desoldering "bulb" from Radio Shack for a few bucks. That should work wonders for you.

http://www.radioshack.com/product/index.jsp?productId=2062742

those bulbs suck, get the spring loaded ones from ebay for the same price.

You are right about that. But the bulb is a better solution that what he proposed. I was just trying to recommend something readily available at the local level and cheap.

This is the ideal tool to use: http://www.parts-express.com/pe/showdetl.cfm?partnumber=372-202

Infact, I recommend spending the money on it because, in my experience, once you start soldering stuff, it'll open doors to lots of future projects. It's a great skill to have!

I'd have to second the recommendation for a de-soldering iron. Those things are infinitely more useful for repair work than unpowered bulbs or spring loaded solder suckers. This is especially true now in our brave new world of lead-free solder where you can't safely get enough heat into a joint to keep it liquid long enough to get good suction using a solder sucker.

If you are unskilled at soldering, completely removing the old capacitor may be dangerous; it is easy to either lift a circuit board trace (if you are trying to use something like solder wick), and it's also easy to loose the through-hole plating if you don't know what you are doing. If you do desolder, practice on some junk pile boards first. You also might want to get some flux to help.

The easiest way, and least likely to harm the board, is cut the old capacitor off, trim the new capacitor's legs down to 1/2 or 1/4 their original length (leaving 1/4 inch or so to work with). 'Tin' the ends of the new capacitor's legs with some solder. Then melt a small amount on the old stumps sticking out of the board. Melt the new legs and old stump together into a small solder blob. Just don't let the small solder blobs touch any other traces, or short the two legs of the capacitor together.

Will this alter the overall capacitance? Not at all: The parasitic capacitance of leaving the old legs on, or having legs too long, etc is minuscule compared to the actual capacitor. The parasitic capacitance will be in the pF range; if you are replacing a 1 uF capacitor, with a tolerance rating of 1%, then the capacitor's value will already vary from the factory by 1% of 1uF, which is 10000 pF. A lot of time, capacitor rating is only 5% anyway, so probably 50000pF. I would not worry about adding another 50 pf to that. You're talking about altering a 5% variance by less than 1% of the variance. As capacitors age, their value goes out of spec a lot more than this anyway; if you took out a capacitor from a 5 year board, it could be off by quite a bit!

Replace your old capacitor whatever way you are most comfortable and confident in doing with your skill set.

Also note, that the above does not hold true for small value capacitors. If you have a tiny .001uF capacitor, maybe you will start to see a difference from the component legs.