I have two 48" fluorescent fixtures in my kitchen, each with four bulbs. They're old fixtures (maybe 25 years old), and I replaced the ballasts in both fixtures a couple years ago.
Recently, one of the fixtures stopped working completely. Actually, not quite completely: one of the four bulbs flickers dimly. I replaced all four bulbs and there was no change. The new bulb in the same slot still flickers dimly, and the other three new bulbs are effectively dead.
What could be happening? Bad ballast? Grounding problem? Any guesses, based on the symptoms?