Had a similar issues with my 4900. You could barely see the game playing in the back but the screen was green. Turns out my tube had carbon built up on the guns that was shorting it. Had to put it on a rejuvenator which fixed the issue immediately! I now have another tube doing it as well but the game is more visible, so I am going to rejuvenate that one too. Issue here is that rejuvenating has the possibility of trashing the tube if it's on its last legs.....but can also save it lol