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Thread: How to check flourescent light transformer...

  1. #1
    Join Date
    Jan 2004
    Thanked 27 Times in 26 Posts

    How to check flourescent light transformer...

    F32TB/TL850 is the transformer number. Typical 4' fixture. New bulbs did not help. There is 120V at the fixture. Is there a way to verify the transformer? What voltage should I expect at the pin ends?

  2. #2
    Join Date
    Jul 2004
    Saint Regis Falls, NY, USA.
    Thanked 478 Times in 465 Posts
    as a rule expect to find at least 750 volts to vaporize the mercury pellet inside. once the tube "fires" the voltage drops to a minimal to maintain the arc. Ideal makes a ballast tester.

  3. #3
    Join Date
    Dec 2008
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    I did electronic trouble shooting for many years. I found that logic could oftentimes be used to solve problems faster than any "test" equipment. Here's how. To logically check a transformer, or ballast, measure the input voltage (117 line voltage). If voltage present, insert a NEW bulb and turn on the switch. If it lights, the ballast is good! If it doesn't light, the ballast is bad. The simple truth here is that there are only 3 links in this working chain. The AC power, the ballast (and starter if you have one), and the bulb. A fourth link may be the light switch, a fifth may be the panel breaker, and a sixth may be the power company. But in your case, if you have the cover off of the lamp fixture circuit, you have the three links you can check. Of course if the first link, the AC power, is not there, then you need to look back to the other links, that is, light switch etc.. I hope this helps for future problems too. Oh yes, I know, you do need a voltmeter to point to the links, but the best "test" instrument is your thought process.

    I think it also helps to understand that some of the things we call "test" equipment don't really test anything. A voltmeter for example, only gives you measurements.However, if your lamp doesn't work and you put in a new lamp and turn the switch on, that is indeed, a test. Another example of a test is, if you suspect a loose wire on a switch and then tighten the screw, when you turn on the switch, that is a test. You can learn as much from a test as you can by making measurements with some piece of equipment like a voltmeter. In the example of the suspected ballast, you measure voltage, then test with a new bulb. Just turning on the light switch is a test of the entire system. If you turn it on and the light lights up, you have tested the entire working chain and it is good. If no light then you begin a series of tests and measurements. The trick to trouble shooting is to mentally separate the circuit into it's components and then see how you can make measurements and apply tests to narrow the problem to a single component. Hope this helps.

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