The only other thing I can think of if you're still having issues would be to check continuity from the Cartridge Slot pins back to the original pins on the CPU and RCP. Here is a diagram from a long lost website, all credit to the almighty @ShockSlayer for this!! 
http://forums.modretro.com/index.php?threads/rcp-relocation-guide.2428/

http://forums.modretro.com/index.php?threads/rcp-relocation-guide.2428/