2 x 0805 100nf caps added to the bottom of the board.
Test candidate is a Mega 1 that's been upgraded to 4mb using SOJ20 adaptors and smt ram, with the extra wired wired to the top of the MMU socket.
I had to temporarily remove the extra wire, putting the machine back to 1mb mode. Really must stop being lazy and connect this properly on the bottom of the pcb.
The good news is the board boots first time with tos 1.04 but only shows 512k. Checked again by booting with z diag cart and it still only shows 520k. Putting the normal MMU in returns the ram back to 1mb. So I guess I've either got a dry joint on a track or I need to fit an unf*ck wire somewhere.
Definitely going in the right direction though, so well done exxos
If it ain't broke, test it to Destruction.