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magnavox 42" inch rear projection tv

Discussion in 'Electronic Repair' started by Karthik, Mar 16, 2006.

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  1. Karthik

    Karthik Guest

    i have a magnavox 42" inch rear projection tv, the tv works fine and
    has no problems, the one problem it has is that the screen is a little
    cloudy. I am thinking that the coolant fluid needs to be changed. Do
    you think this is the only issue. Also, can you guide me on how i can
    change the fluid myself and where i can buy it. you can email me at


    Thank you,
     
  2. Bill S.

    Bill S. Guest

    Without a model or chassis number, I'll speak in generalities.

    You might want to check the main mirror first. It picks up a film of
    nicotine, cooking grease, dust, etc. that can scatter a lot of light.
    But having said that...

    Cloudy fluid is a common problem on these. There is some type of
    bacteria or algae that lives in the tubes' cooling chambers and gets
    its energy from the light generated by the tubes. It especially likes
    blue light, and you will find the blue tube to be the worst.

    The factory expects you to remove the tubes from the set, but many of
    us in the field do the job in situ to save labor and minimize disturbing
    alignment and connections.

    Older models can be sucked out and refilled by removing the expansion
    chambers, which are all located on the uphill side of the tubes. Newer
    models have a drain/fill plug and separate expansion chamber, and some
    have the tubes oriented differently so that you have to tip the set
    backward to suck out and fill one of the tubes.

    Older models do not have any circuit boards under the tubes, but newer
    ones do, and you need to make sure you do not drip any of the cooling
    fluid on the board because it is slightly conductive and can cause
    electrical damage.

    On the newer style with the diaphragm expansion chamber, I like to put
    a piece of electrical tape over the vent hole so that a cushion of air
    is trapped which prevents movement of the diaphragm. It gets removed
    later. I don't normally disassemble the diaphragm type expansion
    chambers.

    With some kind of pump and medical or aquarium tubing, suck out as much
    of the fluid as you can get. Remove the lens and "C" element from the
    front of the tube (the "C" element is an inverted dome optical window
    into the cooling chamber). Clean the heck out of everything, put it
    back together in reverse order and refill. Don't forget the big mirror
    in the back. Toilet tissue or paper towels, windex or maybe alcohol
    for stubborn encrustations, finish with something lint-free.

    I didn't mention what you have to do to get at the tubes, which varies
    a bit depending on model, probably can figure that out yourself.
    Typically takes about 3 hours for an experienced tech (which is one of
    the reasons it costs so much). If you've never done it before, it will
    probably take all day, depending on aptitude, tools, etc. Fluid, pump,
    tools, etc. are available from most electronics supply houses. I use
    MCM Electronics (www.mcminone.com) because they are relatively close to
    me and stuff ordered usually arrives the next day.

    Have fun. Check back with a model or chassis number for more specific
    details.
     
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