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  1. #1
    AgX
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    neon indicator lamp failure

    On fleamarket found electronic flashlights (solo or in-camera) I repeatedly found samples that flash but nevertheless show no glow ("loaded" sign) at their indicator neon lamp. And I waited for some minutes to exclude cases were the circuit permits flashing before the break-through current of the lamp is reached.

    Typically these types of lamps go for many thousands of hours.

    Any ideas about the cause of such failures aside of a broken connection?
    (Another cause might be a too high current through the lamp, and thus destroying it. Though I got no idea how such a current could arise.)

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    Neon bulbs don't last forever. In addition, there is typically a RC (Resistor and Capacitor) circuit used to make to lamp flash (blink); this could easily go bad.

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    I have seen this symptom many times but it is not the neon bulb that is failing but the main capacitor that powers the flash. Neon bulbs have a long useful life, far longer than that of capacitors. When the neon bulb no longer lights or is slow to light it indicates that the capaacitor is no longer capable of holding a full charge. The unit may still flash but not at maximum output. The condition will continue to get worse until the unit no longer will flash.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  4. #4
    Leigh B's Avatar
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    Quote Originally Posted by Gerald C Koch View Post
    ...it is not the neon bulb that is failing but the main capacitor that powers the flash.
    Yeah... What he said ^^^.

    Capacitor failure is extremely common, almost guaranteed if the flash is more than ten years old.

    It's an easy fix (replace the capacitor), but may not be worth the cost depending on the size and quality of the unit.

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  5. #5
    AgX
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    Gerald, good point in drawing my attention to the main capacitator.

    My idea though was/is that in case the main capacitator won't have it's full capacity any longer, the voltage will finally still rise up to the charging voltage. The lamp will glow (though no longer indicating the fully or rather sufficiently loaded state of the main capacitator).

    However, in case that loss of capacity is due to a "electrical leakage" of the capacitator, I guess there might be a situation where at the capacitator is a lower voltage, still sufficient to flash the flash bulb but not to make the neon bulb glow.

    This all makes me realize I did not yet consider sufficiently the issues of capacitators...

  6. #6
    Bill Burk's Avatar
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    Quote Originally Posted by Leigh B View Post
    Yeah... What he said ^^^.

    Capacitor failure is extremely common, almost guaranteed if the flash is more than ten years old.

    It's an easy fix (replace the capacitor), but may not be worth the cost depending on the size and quality of the unit.

    - Leigh
    Yeah, what they both said ^^^.

    The issue is that you get up to 80% full charge, maybe, just enough to flash. But not the right amount of light to use the chart for proper exposure.

  7. #7
    Leigh B's Avatar
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    The problem is not loss of capacitance, it's leakage.

    Leakage will prevent the capacitor from charging to its full voltage.

    The neon indicator is a voltage comparator circuit. It comes on when the voltage across the capacitor rises above 250 volts (for example).
    If the voltage can only rise to 240 volts, the neon indicator will never light, but the flash may still fire at reduced brightness.

    This is the way flash systems work. I was a warranty repair station for Novatron strobes, so I'm reasonably familiar with the technology.

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  8. #8
    mr rusty's Avatar
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    May I just had, don't mess with trying to repair flashes if you don't really know what you are doing. I didn't and did. I had a "little knowledge" that discharging the capaitor might be a good idea. The bang when the screwdriver shunted the terminals was something else and scared the s***s out of me. Decided I wouldn't do that again!

  9. #9
    Steve Smith's Avatar
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    Capacitors like to be discharged slowly with a resistor, not suddenly with a screwdriver. However, in practice, discharging the capacitor into the flash tube is closer to the screwdriver method than the resistor method!


    Steve.

  10. #10
    Steve Smith's Avatar
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    It probably harms the screwdriver more than the capacitor.

    EDIT: How did that become two posts? I thought I just added to the first one!


    Steve.

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