I'd be interested in a better picture of those chips along the bottom of the board. The only picture I could find showed just the corner of the chips which looked like some kind of Kyocera "KM41..." and below it "513..." they look like a RAM array which would fit with what H3NRY indicated was needed for a signal converter.

I wonder why the 512K won't start up with the board. Could it be a failed component, or might the board require special startup software? What exactly happens when you try to start up with the board in? Do you get a bong? Do you get a flashing question mark, or just a black screen?