In article , dgk wrote:

A fixture in my basement has a single 48" florescent tube which
recently started flickering and now fails to start - it just flickers.
I replaced it and have the same behavior. The fixture is at least 15
years old and might be much older.

I don't see anything that looks like a starter. I've searched around
and see that the ballast may be the problem, but I don't see what
looks like a ballast. It may very well be under a metal cover that
runs most of the way under the bulb. Well, above the bulb actually.

This sounds like a starter, which in a few fixtures can only be replaced
if the fixture is opened. Starters are usually but not always accessible
if the fixture is only disassembled enough to remove the bulb.

Replaceable starters are cylindrical "cans" about 3/4 inch in diameter
and about 1.5 inches tall. Twist counterclockwise about 1/4 turn (maybe
somewhat less) and then pull to remove. For a 4-footer, the replacement
starter is an FS-4.

- Don Klipstein )