Excalibur board- tweaking possible?

[volcanohead]

I have the Excalibur board, which runs well except for a few dead spots. I was wondering if there was a way to fix these dead spots. I noticed that there are screws on the bottom holding the board to the frame; would I be able to correct the dead spots by tightening those? If so, how? Are there other ways to tweak this board? Thanks for your time.