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I am trying to debug a failed fluorescent light fixture. T8, 1x36W. I have checked the tube (vs. both a new one and a known working one), and this is not the problem. So I thought it must be the electronic ballast ("preheating start" type). What is confusing me though is that there is power both going into and out of the ballast (and also reaching the actual clamps for the tube light). So my question is: is it possible that the ballast is broken, but that there is still power coming out of it? By "power" I mean there is enough voltage across the output terminals of the ballast to light up a phase tester screwdriver. Thanks! PS. This setup does not have a separate starter.

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    \$\begingroup\$ How an electronic device fails cannot always be predicted. A device will only fail in a predictable way if it was designed to do so and the condition causing the failure is within certain limits. Without knowing 1) the exact design of the ballast 2) the exact conditions that made it fail 3) failure analysis of the ballast it is impossible to answer your question other than "Yes it is possible". \$\endgroup\$
    – Bimpelrekkie
    Commented Jan 9, 2020 at 10:52
  • \$\begingroup\$ A "phase tester screwdriver" will detect any electrical field over \$x\$ intensity, regardless of any other considerations. But at least two supplies power a fluorescent lamp - one for the filaments and another between the filaments. So this tool is incapable of determining which of the two has failed, since they are electrically common. Regardless, a new ballast is the solution. \$\endgroup\$
    – rdtsc
    Commented Jan 9, 2020 at 13:06
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    \$\begingroup\$ "is it possible that the ballast is broken, but that there is still power coming out of it?" - yes. \$\endgroup\$
    – Bruce Abbott
    Commented Jan 9, 2020 at 18:30

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Thanks for your comments. I put in a new ballast and that did the trick. So to answer the original question, and as indicated in the comments, just because there is power flowing out of the ballast does not mean that the ballast is ok.

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