Don't really need a Schematic to troubleshoot the board.. Should be a simple circuit anyways.
1/ Check all circuit for broken tracks.
2/ Check electrolytic caps for leakage and bulging tops/bottoms.. You might want to replace these anyways.
3/ Check hookup wire to other socket.. Make sure the solder joint is of good quality.
4/ Check connector to make sure its mating correctly with amiga.
5/ Clean up all those IC's in sockets.. Following anti-static procedures, take out all the IC's from their sockets and give them a bath in lemon juice to clean the legs... (A favourite @ Amibay)
Use some isopropyl alcohol to clean up the sockets if you can and residue from lemon juice on IC's..
If that doesn't work, assume a few dead IC's here and there.. Get another unit should be able to come across one for cheap $$
