Headphones not working, even after I replaced the jack

A couple of months ago I messed with an electric guitar amplifier, trying to use the iphone as speakers (there was an app for that).

I did a stupid thing, plugging the amp out to the audio jack (I know, it was idiotic).

After that, I couldn't hear music through headphones anymore, but the headphones controls still worked (i.e.: could still play/pause music through the buttons on the headphones) .

I thought I might have broken the audio jack, so I replaced it. The replacement went fine (that is: volume control, mute switch, headphones' controls work), yet I still can't hear any sound from the headphones.

I guess I broke the chip on the logic board which manages headphones' output (though it's weird that headphones' controls still work).

Now my question: any ideas about where to get a new logic board? Any alternative fixes?

Remark: I don't want to bring my iPhone to an Apple store.

Thanks to everyone