Doh! That sorted it out, I at least have sound now, thanks! Do you think it is still worth getting a ram cartridge though? It seems that you can get blank ones on ebay. Could I maybe get patches from the internet and then dump them onto the cartridge somehow?
Also, another question, is there some way to restore the factory settings on the internal memory on the DX7? It seems the previous owner has written over some of them since quite a few of them have the same name but sound different. I saw the names of the internal memory patches in the user manual and they were different to what I have.