I have a Mac Classic that is displaying a checkerboard at startup. Simple fix, right? replace the caps on the logic board.. Well, I did that but it's still displaying the exact same checkerboard pattern. I have a working Mac Classic - swapped this logic board into the working machine to just verify the analog board is OK - same pattern. What else could be wrong with it? do I need to desolder/replace the RAM chips? Can you piggyback test these chips?