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LCD projector

Discussion in 'Electronic Repair' started by bart bervoets, Jan 30, 2005.

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  1. Is it possible to make a unit power up without bulb?
    Unit goes in standby.
    As well, any way to convert the lamphouse to use a cheaper lamp?
    How hot do halide bulbs get?

    Bart Bervoets
     
  2. James Sweet

    James Sweet Guest

    No there's no practical way to convert it to a different type of bulb, they
    use expensive metal halide lamps for a reason. They reach very high
    temperatures, but the actual amount of heat they put out is substantially
    lower than a halogen bulb of the same wattage.
     
  3. Powering up w/out bulb:
    Yes. Look for the circuit board that has two heavily insulated wires (has
    25KV on them) going to bulb. There is proabably 2-3 signal wires nearby.
    Something can usually be done to provide a signal, the signal basically is
    on/off low voltage, and the signal just tells the rest of the projector that
    the bulb powered up ok.
    I've used an alternate projector bulb on my TV for the last 100 hours or so,
    works fine. Original cost about $300, I got the cheapest UHP off of eBay for
    $23 delivered and adapted it. Original was 100 watts, 3" diameter,
    replacement was 120/132 watts, 1.5" diameter. CPU fan provides additional
    cooling.
    The light from both bulbs gets focused very effeciently down to 1/8"
    diameter spot from the reflector shape. Your replacement bulb will have to
    do likewise.
    There is a really good chance of electrocuting yourself or blowing up your
    circuitry trying to do the same thing I did. The halide bulbs can explode
    quite well; safety glasses/shield and high collar jacket are minimal safety
    standards. I alpha tested mine on New Year's eve on my front porch.
     
  4. James Sweet

    James Sweet Guest

    What are you using to ballast the new bulb? I'd be very hesitant to go up in
    wattage, in that unlikely scenario that it catches fire, you're pretty well
    screwed.
     
  5. 25KV to start an arc, then about 20-50 volts to maintain the arc. So of
    course I am using the original ballast (100 watt) with the slightly higher
    (120 watt) bulb. The ballast is specifically designed to limit current, or
    you could say regulate current, so I am pretty sure it is only putting out
    100 watts, although it might be generating a slightly different voltage to
    do so, which is really a function of the electrode gap. Thus it might be
    getting a little hotter, hence the extra fans. This LCD projection tv had
    30,000 hours on it when I got it for $1.25, but it really does look great. I
    have no worry about it catching fire, but there could be a component failure
    in it's future.

    On the other hand, putting a lower watt bulb than the ballast is designed to
    use will result in a very hot bulb explosion rather quickly, as the ballast
    IS going to put out the same wattage regardless of which bulb is in place.

    Normally, the problem of switching bulbs is that the ballast will not start
    the arc at all. But I got lucky and it starts on the first attempt every
    time.
     
  6. James Sweet

    James Sweet Guest

    Ah, I thought you were using something else as the post was originally about
    tricking the projector into thinking the lamp had started.

    Using a lower wattage lamp is safe, though often you'll get a nasty color
    shift if you operate a metal halide out of spec but that depends on the
    design of the lamp. Also, surprising as it may be, operating them under
    wattage will usually drastically decrease lamp life because the electrodes
    run too cool and sputter heavily as the arc restrikes between the
    half-cycles. YMMV though, for what you have invested in it it's a worthwhile
    experiment.
     
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