Fluorescent fixtures require ballasts to operate fluorescent light bulbs. The ballast provides the proper amount of voltage to start the bulbs and continues to regulate the voltage while the fixture operates. Ballasts are not one-size-fits-all; they are designed for use with specific types and wattages of fluorescent bulb. The average life of a ballast is about 50,000 hours, but some environmental and electrical issues can shorten that lifespan and even damage the ballast, requiring the installation of a new ballast in the light fixture.
Replace the fluorescent light bulbs in the fixture if the bulbs fail to light, if they flicker, or the bulbs are slow to start. If the new fluorescent bulbs fail to operate properly, test the florescent socket before you move on to the ballast.
Remove one of the florescent light bulbs. Set a two-lead multimeter electrical tester dial to 250 AC. Insert both leads into each side of one florescent socket. The meter should register between 3 and 5 volts. Replace the ballast if the meter registers anything other than the stated voltage.
Remove the fluorescent light bulbs from the florescent light fixture. Open the center of the fixture to expose the ballast. The center cover is secures to the fixture with screws or inserts into slots cut in the metal of the fixture.
Inspect the exposed ballast. The ballast is bad if it appears charred or oozes a thick, gooey black substance.
Insert one tester lead into the wire connector holding the ballast's black wire to the black wire from the house wires. Insert the remaining tester lead into the connector holding the ballast's white wire to the white wire from the house wiring. The tester should register between 115 and 125 volts.
Unplug the fluorescent fixture from the electrical outlet if it plugs into the wall. Turn off the breaker inside your service panel that supplies power to your fluorescent light if it is hard-wired into the circuit.
Remove and replace all the wire connectors on the ballast wiring to tighten all connections. Tighten the screws holding the ballast to the fixture. Both these steps can correct a humming ballast. Replace the ballast if it continues to hum once you reconnect the fixture to the electricity.
Check the temperature rating printed on the label of the ballast. Ballasts have different temperature ratings to operate in different environments. If the ambient temperature around your fluorescent fixture is higher than the highest temperature rating for the ballast or lower than the lowest rating, the ballast may not be bad but should be replaced with a ballast rated for the installation location.
Look at the ballast label and check which fluorescent bulbs the ballast should use and the minimum and maximum wattage of those bulbs. The life of the bulb may be shortened if you are using the wrong fluorescent bulb. Install the correct fluorescent bulbs once you reconnect the fixture to the electricity. You may need to replace the ballast if the new bulbs fail to light. Operating a florescent fixture with the wrong type and wattage of fluorescent bulbs can shorten the life of the ballast.