These things were not built to be worked on. Outside of repair the cable I know of no one that has been successful opening and fixing one. That given, here's a pictorial on how one guy got it: http://www.instructables.com/id/MacBook-Mag-Safe-Charger-Budget-Repair-Disas/step2/Disassembly-of-Power-Brick-Brute-Force-Attack/
+
Here's a video on another way to open it and repair the cable: http://www.youtube.com/watch?v=20vLvXUfrIA&feature=related
These things were not built to be worked on. Outside of repair the cable I know of no one that has been successful opening and fixing one. That given, here's a pictorial on how one guy got it: http://www.instructables.com/id/MacBook-Mag-Safe-Charger-Budget-Repair-Disas/step2/Disassembly-of-Power-Brick-Brute-Force-Attack/