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metal halide bulbs testing?

Discussion in 'Electronic Repair' started by Steve Vitale, Oct 29, 2004.

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  1. Steve Vitale

    Steve Vitale Guest

    Hi all, I have an sharp XG-E3500U lcd projector that i'm trying to repair,
    I've purchased a copy of the service manual (email me off list if you'd
    like a copy) and have a pretty good idea of how things are working. when i
    got the unit, the main fuse on the power board was blown and the person
    who gave it to me suspected that the power supply was bad. when i replace
    the fuse and power up, the lamp arcs 2-3 but never lights. the fuse blows
    immediately afterward. my assumption is that either the warm-up arc isn't
    able to ignite the lamp because it's bad, or that the lower voltage
    componant supplied by the ballast is isn't there so the thing keeps
    pulsing then blows a fuse. Will a bad bulb cause a fuse to blow because it
    won't conduct a current after being hit with the warm up arc? I figured
    I'd send a message to the list to get an opinion before i spend $300 on a
    new bulb.. maybe i need to focus more on trouble shooting the ballast. Is
    there an easy check for visual or electronic signs of a bad metal halide
    bulb? Thanks for any help, Steve

    p.s., please don't warn me about the high voltage.. i may sound like a
    novice but my heart is healthy and i'm quite intent on getting this thing
    to work.
     
  2. NSM

    NSM Guest

    | Hi all, I have an sharp XG-E3500U lcd projector that i'm trying to repair,
    | I've purchased a copy of the service manual (email me off list if you'd
    | like a copy) and have a pretty good idea of how things are working. when i
    | got the unit, the main fuse on the power board was blown and the person
    | who gave it to me suspected that the power supply was bad. when i replace
    | the fuse and power up, the lamp arcs 2-3 but never lights. the fuse blows
    | immediately afterward. my assumption is that either the warm-up arc isn't
    | able to ignite the lamp because it's bad, or that the lower voltage
    | componant supplied by the ballast is isn't there so the thing keeps
    | pulsing then blows a fuse. Will a bad bulb cause a fuse to blow because it
    | won't conduct a current after being hit with the warm up arc? I figured
    | I'd send a message to the list to get an opinion before i spend $300 on a
    | new bulb.. maybe i need to focus more on trouble shooting the ballast. Is
    | there an easy check for visual or electronic signs of a bad metal halide
    | bulb? Thanks for any help, Steve

    That's backwards. I'd suspect the ballast, not the lamp. Is the ballast
    inductive or solid state? I'd try hooking up a 100 W light bulb as a test to
    replace the lamp, disconnecting the starter system if possible. If the lamp
    glows fully or not at all I'd suspect the ballast.

    N
     
  3. Steve Vitale

    Steve Vitale Guest

    That's backwards. I'd suspect the ballast, not the lamp. Is the ballast
    I assume that it's an electronic ballast as it uses transistors to limit
    current as opposed to a coil. i assume those should be keeping things
    from reaching a current where a fuse would blow? i think this is starting
    to make a bit more sense.
    Thanks
     
  4. NSM

    NSM Guest

    | > That's backwards. I'd suspect the ballast, not the lamp. Is the ballast
    | > inductive or solid state? I'd try hooking up a 100 W light bulb as a
    test to
    | > replace the lamp, disconnecting the starter system if possible. If the
    lamp
    | > glows fully or not at all I'd suspect the ballast.
    | >
    | > N
    | I assume that it's an electronic ballast as it uses transistors to limit
    | current as opposed to a coil. i assume those should be keeping things
    | from reaching a current where a fuse would blow? i think this is starting
    | to make a bit more sense.
    | Thanks

    Much more likely one of those has punched through. Replace them or find a
    way to test them under voltage.

    N
     
  5. James Sweet

    James Sweet Guest


    If the fuse blows you have a problem with the ballast. An electronic ballast
    still uses a transformer, it's more like a switching power supply in a PC,
    monitor, etc, but rather than regulate the output voltage it regulates the
    amperage as well as provides a high voltage spike to strike the arc. Check
    carefully for shorted semiconductors in the ballast circuit.
     
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