Yeah, its the caps like Uniserver says. After they are replaced, the analog board needs to adjusted. To clean out potentiometers get what is known as "TV Tuner Cleaner" from your electronics store or "Power Window Switch Cleaner" in the automotive store and zap the potentiometers with the spray a couple of times. Let it dry out. Then turn it on and make the adjustments as needed.

First adjustment - in a dark room, adjust the brightness so there is no grey around the display (like there is on your pic). That will balance out the black as black. Then adjust the contrast until it is sharp (and the dark area is still black); you may need to tweak the brightness after adjusting the contrast.

Then adjust size the screen as per Larry Pina Specs for a B/W Mac. Finally adjust the centering of the display.