Gameboy DMG sound not working

[perhotspur]

I've trying to get my old Gameboy DMG working. I've fixed the vertical lines on my screen. But the sound does not work from the speaker. I've spent a lot of time looking around the net for solutions. I've tried everything. Changed the speaker, re-soldered the cables for it. I've even disconnected the cables for the headphone outlet incase something in there was stuck shutting of the speaker. I've cleaned up the whole gameboy and it looks really nice. But there are no sound. Ive been looking high and low for some explanation/schematics for how the sound is transfered from the board with the cartridge and on to the board with the screen. I just cant figure it out, which makes it really difficult to find out what is wrong.

Can anyone help me out? Any information or tip will be very helpful.

 

[uXe]

This pinout might help:

http://www.robotdialogs.com/2010/03/gameboy-classic-work-in-progress.html

Pin 20 on the ribbon cable is the Speaker signal - if you have cut the wires to the headphone board though keep in mind that one of those wires is a 'switch' to turn the speaker on / off when the headphones are plugged in!