So then it seems the actual "tunneling" issue (gradual darkening of the corners after the computer has been on awhile) as opposed to contrast issues (like techknights) is - as far as we can tell - most likely an issue with the LCD screen in specifically active-matrix/greyscale like the 540(nonC) ?

If this is the case, putting another active-matrix/greyscale screen in there is not really a fix as all of them will eventually have this issue.

I wonder what would happen if I put a passive-matrix lcd (from a 520) in there (either nothing or it might function like a 520?) ....or maybe even a color active from a 540c ? (I know it would only display greyscale if it even worked.)

Or do the exact logic boards need to match the exact lcds for the 520,520c,540,540c,550c respectively ?

Are we pretty convinced tunneling can not be related to caps ?

Has anyone seen the tunneling issue on anything other than an active-matrix/greyscale lcd ?