Fluorescent light fixture repair may be more simple than you think. Basically, there are only 4 likely things that will cause one of these fixtures to stop working: power failure, bulb failure, ballast failure, or tombstone failure. Starters, used in older fixtures, can also cause problems, but newer fixtures do not use these components. Once you have narrowed the light fixture failure to the right component, repair will be relatively simple. Just follow the 5 steps below.
Step 1 – Use Prescribed Check Order
Your job will be easier if you use a prescribed order for checking lighting fixture components. First, check electrical power, then the light bulb, the ballast, and finally check the tombstone.
Step 2 – Check Electrical Power
If you have more than 1 bulb in your fixture, and if at least one of the bulbs is lighted, you can be sure the fixture is supplied with power. There is no need to check for power, in this case. One sign of a failed fluorescent bulb is a black end on the bulb. Even if the bulb with the black end is lighted, you should replace it to keep it from overworking the ballast. If all bulbs are unlighted and none have black ends, check the power switch o be sure it is on. Check other fixtures or appliances operating from the same light switch as the fluorescent fixture. If they are working, you can safely assume power is not the problem. If they share power from the same circuit as the fixture but are not working, then power is likely the source of the problem.
Step 3 – Disconnect Power to the Ballasts
Ballast secondary output voltage can be dangerously high, so disconnect the ballast's white and black wires before you begin working on one these fixtures. This will remove primary voltage from the ballast. But use caution in doing this.
Step 4 – Check the Ballast
Expose the ballast by removing the fixture's center cover. Typically, each ballast services two bulbs, with 1 ballast serving the 2 middle bulbs and the other ballast serving the two outside bulbs. A possible exception is an electronic ballast that serves all 4 bulbs. If either pair of bulbs, the inside or the outside pair, is working, you can figure that the ballast that serves them is still in good working order. If one pair works, but the other pair does not work, more than likely the non-working pair will need to be replaced.
Step 5 - Replace Failed Ballasts
To replace the defective ballast(s), loosen or remove the nuts holding the ballast in place, then replace it with a new ballast. In reattaching it, match wire colors correctly, using wire nuts. Then replace the ballast cover, plug in the new bulbs, and test the light fixture.
Step 6 - Replace Tombstones
If all the above steps fail to repair your fixture, chances are good that the problem is in the tombstone sockets holding the bulbs. Remove the defective socket by pulling out the metal insert holding it in place, then pull the socket wires out of the slot into which they are inserted.