I’ve just been forced to try to replace the power switch on my daughters Nintendo DS Lite, after it broke off, but no-one seems to know how, or at least no-one is admitting to it!! I manage to find a replacement switch on eBay for £4 and although its been years since I tried to solder anything I gave it a try. Removing the back of the bottom case is fairly straight forward but you need a special TRI-WING screwdriver for some of the screws, (£1.50 on eBay). The power switch is in the top left corner.
I thought de-soldering the switch would be tricky, but as it turns out the connectors for the switch simply sit on top of the board and do not go through holes in the board. A de-soldering tool was really helpful here. Once removed, replacing the switch was, again, surprisingly straight forward. there are four connectors on the power switch, each has to be soldered back on, see the red squares in the opposite picture. As you can tell from the picture, my attempts at soldering do not look great, but it worked ! once I had the case back on I realised that the power switch was ever so slightly mis-aligned on the board. This meant that once the case was back on, the switch was slightly more stiff than without the case on. But for less than £6, rather than £100 to buy a new SD, I’m not complaining