Any electrical whizzes out there to help me debug my light fixture issue?  (see details)?

I have an under-cabinet fluorescent light fixture w/T5-type tube bulb. It has a switch but is also hardwired to a wall switch, so I use the wall switch and keep the fixture “on” all the time.

After years of normal operation, it now fails. Observations:

1. The problem is that the light, after being on for awhile, suddenly goes out (looks like it was turned off).

2. The problem is intermittent, and the length of “on time” before the problem occurs varies and is unpredictable.

3. The light never flickers or lights dimly at any time.

4. I’ve replaced the bulb, but the problem is exactly the same.

5. Light cannot be controlled from anywhere else.

6. When the problem happens, I can usually fix it by turning either the wall switch or the fixture switch off and then on again. This usually works if the light’s been off awhile. If I try it immediately after the failure, it sometimes won’t work.

7. In those cases, I CAN restart the light if I turn BOTH the fixture AND wall switches off and then on again.

8. Today, when the problem occurred, I carefully removed the bulb, and tested the “pin socket” at each end of the fixture with a non-contact voltage detector. There was power at both ends. I flipped off the wall switch. No power at either end. Wall switch back on, power. Fixture switch off, no power. Back on, power. No surprises. Reinsert bulb, and it does NOT come on! Now I turn BOTH switches off, then on. Light comes on!

Any ideas? What could be wrong with this fixture?

7 Answers

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  • Droopy
    Lv 5
    2 months ago
    Favourite answer

    There's probably a issue with the ballast or transformer that's converting the 120v to the proper voltage for your light.  It's probably overheating.  Which causes a safety to open turning light off.  Then once it cools down it closes allowing the light to turn on.

    • D H2 months agoReport

      I'll check that, thank you.  I didn't think a bad ballast could manifest itself as an "overheat/shutoff" issue.  Since you say it can, I'm pretty sure that must be the problem.  Thanks!

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  • Anonymous
    2 months ago

    Bond and droopy have the correct answer 

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  • 2 months ago

    Get rid of it and install a new unit using LED bulbs.

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  • Edwena
    Lv 7
    2 months ago

    You might try taking it out from underneath the counter. Working upside down always makes things more complicated. It could be your wall light switch or the connections at that switch. After years of operation, they do wear out. You might have had a bug/ant get on the contact when you turned it on and got smashed/fried. But, I would separate the light from the wall switch wiring and see which one is working right.

    • D H2 months agoReport

      all good thoughts, thank you!

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  • 2 months ago

    the ballast likely needs to be replaced. after "many years" it has failed. your local hardware store will fix you up with the required part. instructions come with. it's a fairly simply DIY task

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  • 2 months ago

    Bad ballast.......

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  • 2 months ago

    It sounds like there is a loose connection inside the fitting, something moving slightly with thermal expansion.

    It could be a screw terminal or the internal switch (or some other part) in the fitting that is failing.

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