No Video, only sound

Hey Everyone, I'm hoping someone with a bit more knowledge on genesis/mega drive systems can help me out here.

I have a model 1 sega mega drive VA4 and I have sound via the headphone socket but no video. This is what I have tried so far.

1 Tried video via RF and the AV port, nothing on either

2 Tapped composite directly from the video chip sony CXA1145 still nothing

3 I have started replacing capacitors, they don't appear damaged or leaking but still no change.

Any suggestions would be greatly appreciated