Sorry should have been clear from start - sound was very very low and just a scratching sound, not No sound...
I just changed all the caps on the IFU board - now have good sound out of the RCA connections on the IFU
One problem left for me now - no CDR playback.
I haven't messed with the pots at all yet, and don't believe they have been.
I got the briefcase setup from a friend who is the king of car boot sales - he got the ifu, cdrom & a core grafx for an unbelievable £10, seller had it in a pile of laptops :p
The core grafx had a HK fitted PAL RF mod, I ripped that out and RGB modded it for him in exchange for the IFU & cdrom as it wouldnt play cdrs & sound was gone...
Thanks for all the help and advice!