So how do I fix my Canon 580ex? Here's the steps. Unfortunately I did not take photos during the process.
Take the batteries out, even with it out you can still get a nice shock, enough to cause you to drop the flash and smash it
1. Small Phillips screw driver used for glasses
2. Long tweezers
I got my part from www.uscamera.com for $17.80
1. Remove the rubber from each side of the flash, careful not to tear it. Use a flat head to get underneath the seems and gently lift. Its only attached by glue
2. Time to unscrew, 14 screws altogether.
-2 on the exterior
-6 underneath the rubber caps - 3 each side
-2 holding the flash bulb and
-4 holding the diffuser panel side
Be sure not to lose any screws while in the process.
3. Once the screws are removed careful to unplug the small computer wire, used for transmitting info inside of your flash, you snap this thing and there goes your TTL.
4. From here remove the back panel and remove the old diffuser.
5. Click in your $17 dollar diffuser, remembering to put it in the correct way.
6. Screw everything back in, use your tweezers for the harder to get to screw spots, put the batteries back, pull out the diffuser, and test fire on your canon camera.
Everything should work as normal, if not you screwed something up.