My SNES looks terrible on my new Samsung LED TV :-(
The picture appears to have a checkerboard pattern / interferance:
After reasearch, I have learnt that the usual RGB Scart cables use composite video as the Sync (Pin 9 on SNES to PIN 20 on scart). This creates havoc on modern day TV's, especially on Samsungs.
How to fix it? Use Luma (PIN 7 on SNES) as the Sync.
Heres what I did.
Take your RGB SNES -> Scart Cable.
Carefully cut the moulded cover down one side so you can open it up
Remove the moulded cover to reveal the insides of the plug
Now locate PIN 9 and PIN 7 (On this cable, PIN 9 is the white wire). Carefully cut around the block of plastic, unsolder the white cable and solder it to PIN 7 (Handily the PIN next to PIN 9 :-))
Replace the rubber moulding, super glue the cut, clean it up and job done!
After sync mod, no more interference, checker board pattern :-)