I just replaced the coil under the Tardis on my Doctor Who. It wasn't popping the ball up. It's a pretty easy to get to repair, so that's a good start. When you put it back together, make sure the wire ramp fits in the right place underneath, or it won't see the ball drop, and make sure it's lined up right on top, otherwise balls will bounce back into the outlane when they drop. (you don't have to unscrew it at all on the top for this repair, so if it's straight now, it should stay that way)
It's such a pita to have to put the glass back on to test it, but the glass sensor switch is in the top back corner, if you stick something in there to hold the switch closed, you can play it with the glass off to test it out.
That "keep hands away from mini-playfield" warning is serious. I've known people that have had a ball get stuck in there as it's coming down, and it chips the wood. It's strong enough to take a finger off if you have your hands in the wrong place. If you are messing with it with the glass off, be careful.
This is my favorite pin, I"m really glad I got one. You'll like it when it's up going again.