Hi I've used a sharp chisel and hammer. No matter how you do it, you'll break some plastic someplace. I have good luck at keeping the main damage inside the cover. The most common failure is the transformer. It will either be burnt up or have an open turn. If it is open, it is usually the wire that runs across the top of the coil and not inside the coil. Of course, it is usually the primary that is open. I find that the turns ratio is usually a nice integer number. In other words, for 120V input, it might have 120 or 240 turns on the primary. Things like that. If the primary is badly burnt, you can use the secondary as a input ( from another AC wall wart ) and a few turns replacing the primary to determine the turns ratio. Also, be warned that the cost of the wire is often more than the value of the wart, unless you have a good source. If you have several scrap warts of the same size, you can often swap coils. Dwight