I sometimes fix chargers if and only if they are genuine, replacements are not worth the time. A lot of the chargers still have the brick working properly, it is the cord that sometimes is chewed up internally, thus creating a short and tripping the internal breaker, and no voltage coming out. What I do is open the charger with a dremel using a diamond cutting wheel for stones, speed set a bit low, and slowly work around, paying attention not to cut too deep. Usually a flat blade screwdriver will pop the case open. I then desolder the DC cord, and then test for voltages. If good, I just replace the DC cord with a good one. Now comes the messy part, putting the charger back together. I clean and smooth out the edges with a boxcutter, and whip up a batch of epoxy. Believe me, if you haven't worked with epoxy, it will be messy, with sticky fingers and epoxy all over the place except where you really want it. I dab the epoxy around the edges and use masking tape to hold everything together, holding still for just a couple of minutes, not more. 3X3 inch squares of paper towels dipped in alcohol does wonders for cleaning the extra epoxy, if there is too much, I scrape the excess off, wiping a lot with the towels. I use epoxy that dries out grey in color, I haven't found any in black, so I do just a bit of touch up with a permanent felt marker. The epoxy usually cures in 24hrs, so after testing again, it's ready for the customer.
Opening the charger is the hardest thing, I have tried just a boxcutter (dangerous!), hammer and strong screwdriver, a hydraulic press (pressing opposite side edges) and just plain whack with a mallet. Nothing really works, only the dremel is good, but it still slow and messy (lots of plastic dust). The problem lies with the plastics used, it is almost like PVC.
By the way, usually a good whack will open any replacement charger, that tells you how cheap they are made.
