I followed this design made by someone else.

Then for the audio:

The points to solder to on the board are marked out in this picture, which I also found elsewhere. 2600 chroma was labelled incorrectly though so I modified that (white arrow). The white wire is 5v (which you'll also need to know). A lot of the pictures I found about this mod were for different models/region. The only one that matched mine, which is a PAL-I system was this picture.

The audio bit is descibed here (scroll down a bit).

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