I've had a 5in black n' white portable TV sitting around for a while with the goal of becoming a simple O-Scope. I finally got around to it a found it was really simple to do.
A few notes: Each coil (vertical and Horizontal) has two wires, they are kinda like speaker coils, so in my case their were just four wires soldered on to a little board mounted on the CRT gun. these coils have A LOT of voltage going through then when on(about 15kV) so DON'T touch them while the TV is on. :) The vertical coil runs a 60Hz instead of ~30Hz for the horizontal, so the vertical coil can display higher frequencies and music better. Older TVs will have H/Vsync pots on the back; tinker with these to make the picture look better.
1. I unsoldered one wire which would cause one of the coils to not work. the test goes like this: if you unsoldered the horizontal coil, you will see a vertical line, if you unsoldered the vertical coil, you will see a horizontal line.
2. So then when you figure out which is which coil(and which two wires are for each coil), move the wires that were soldered to the vertical coil to the horizontal coil. You don't need the original horizontal coil wires, so tape them up /cut them off/unsolder them etc
3. Now you can solder on two more wires(the external signal wires, like a MP3 player) on to the vertical coil.