No sound from Gameboy DMG after case swap

I purchased a clear GB case from Kitch-bent.

I used two donor Gameboys for the swap. As you know the GB is made up of two boards. The back came from a different GB than the front.

I am missing sound from the speakers but headphones work. I replaced the little speaker with one I know is working but nothing comes from it still.

Is different revision front/rear not compatible with speaker?

 

I know when my GB speaker stopped working I just blew the dust out of it. Is the speaker clean?

 

No it is a bit dusty. I might try to clean it.