No backlight, new screen, after water damage

I've been "playing" with a 4s for about a year now. Friend dropped it in water and took it in for repair but they said they couldn't, so she bought a new one and gave me the old one.

I must have put that phone apart at least a dozen time. Last week I did as suggested and soaked the board in high grade isopropyl alcohol, then brushed the connectors and all. With the new screen I had bought, nothing would show up, but connecting to the computer would load in iTunes and I was able to do a restore and update to 7.1. After putting the original screen in, I was then able to see a faint image, so I knew the backlight wasn't working.

I ordered another screen from a different supplier. Replaced, and it's doing the same... no backlight, but otherwise phone is working great (can take pictures, front/back camera, sound works, wifi).

So what's the deal? I read something about a backlight coil on the board, where is this for me to verify if that is the problem? I certainly couldn't fix that. Already put a lot of money in parts trying to fix it, would be nice if this backlight issue was repairable.

Thanks for any inputs.