FMA 2 PS2game, curse of the crimson elixir cheats? FAST?! PLEASE HELP ME!!!!!!!?

I'm stuck on chapter four in the second Fullmetal Alchemist game, Fullmetal Alchemist 2: Curse of the Crimson Elixir. You know, the part where you have to look for the pieces of the slates to open the doors? I found 3, but I can't find the fourth slate!!! I've gone through all the tunnels at least four times each and I still can't find it! will someone please give me a valid cheat to get through these doors! Please and thank you!