How do you know if you have to change a ballast?

I have 3 light fixtures, 2 of which looked like the bulbs were burnt out so when I put in new bulbs and they still didn't work, I learned that's because the ballast needs to be replaced. There is 1 more light fixture that is a two-lamp fixture, and one of the bulbs has burnt out and the other one is still working but the light is very dim. I'm wondering if that fixture needs to get the ballast replaced too because someone told me that if there is light, then the ballast does not need to be replaced.How do you know if you have to change a ballast?
In flourescent fixtures, usually when the ballast is going the lamps flicker - sometimes regularly, sometimes intermittently. Seems as if you just have bad tubes in the fixture. Won't hurt to replace them - and if their light is not up to par, or they flicker, then you know the ballast has to go, too.How do you know if you have to change a ballast?
Try the two new bulbs in it and see what happens.How do you know if you have to change a ballast?
put a fresh bulb in it and if that doesn't fix it you need a balastHow do you know if you have to change a ballast?
Usually they stink, They leak a brown guey substance, get on a ladder or chair and try and smell right in the middle. They are fairly easy to change but sometimes cost more thant the fixture itself.How do you know if you have to change a ballast?
The second one probably just needs the bad bulb replaced.

Usually if the ballst is bad you have noticed a smoky smell at one time or another.How do you know if you have to change a ballast?
It is the earth leakage Dear PD between live and negative droppedHow do you know if you have to change a ballast?
If your going to replace the ballast in one chances are they are all going, for manufacturers seased to manufacture fluerescent lights with ballasts years ago, because the ballasts leak and they give off a harmful gas, I would look for another fixture without a ballast that would fit there, it will cost you about the same as having the ballasts changed in your old lights and you will be more energy efficient.How do you know if you have to change a ballast?
You have just described the exact senario in which you will need to replace the ballast. Just make sure that you did replace all the bulbs, because the other could be out as well. Hope this helps.How do you know if you have to change a ballast?
Everyone Else has covered the ballast troubleshooting thing.

I just wanted to say that if you DO need to replace the ballast. You may want to think about changing the whole fixture as ballast by themselves are 90% of th price of a fixture (unless real decrotive).

to have them shipped is crazy as they weigh so much. most ballast that I have changed have been a real pain and usally invole taking down the fixture any way.

good luckHow do you know if you have to change a ballast?
[pitt 59 got this one right the best answer.How do you know if you have to change a ballast?
if the ballast feels cold it is bad