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Kv-27ts27 color problem

Discussion in 'Electronic Repair' started by Joust, Nov 2, 2005.

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  1. Joust

    Joust Guest

    i have a KV-27ts27 made July 1992
    I'm noticing that red is more brown than red.
    i tried adjusting things a bit but not gotten very good results.
    there is no red drive pot. there is a green drive and a blue drive but no
    red.
    there is a red BKG pot and a blue BKG and a green BKG.

    is there a procedure for tuning color? i made a nice colour bar test pattern
    on my PC and use the tvout from the PC into the video 1 input.

    Wish i could get this set tuned up because it works well other than the poor
    colors. there is definately red there so its not a failed gun. at least not
    completely.

    i have replaced the MPX chip in the past.
    any help would be appreciated.
    Joust
     
  2. Asimov

    Asimov Guest

    "Joust" bravely wrote to "All" (01 Nov 05 20:46:28)
    --- on the heady topic of "Kv-27ts27 color problem"

    Jo> From: "Joust" <>
    Jo> Xref: core-easynews sci.electronics.repair:347167

    Jo> i have a KV-27ts27 made July 1992
    Jo> I'm noticing that red is more brown than red.
    Jo> i tried adjusting things a bit but not gotten very good results.
    Jo> there is no red drive pot. there is a green drive and a blue drive but
    Jo> no red.
    Jo> there is a red BKG pot and a blue BKG and a green BKG.

    Jo> is there a procedure for tuning color? i made a nice colour bar test
    Jo> pattern on my PC and use the tvout from the PC into the video 1 input.

    Jo> Wish i could get this set tuned up because it works well other than
    Jo> the poor colors. there is definately red there so its not a failed
    Jo> gun. at least not completely.

    Jo> i have replaced the MPX chip in the past.
    Jo> any help would be appreciated.
    Jo> Joust


    The drive pots are for the colour gain, an analogy can be made to an
    equalizer control in audio. Only 2 DRIVE pots tells us that the red
    gain is fixed. The green and blue pots are used to match up these
    colours to the red (both typically set at about 1/4 rotation). The
    drive pots are used to set the colour temperature of the bright white.
    The other 3 pots are for setting the bias or the low brightness grays.
    These usually set initially about 1/3 but then more or less depending
    on the health of the colour guns. A weak gun will require more bias
    and more drive. At some point though the internal voltages are upset
    and the gun will both not focus, and converge properly, or even bloom.

    I have a monitor with a bad video processor. Colours are saturated
    with good white and nice gray scale but yellow looks beige as if
    it didn't have enough red gain.

    A*s*i*m*o*v

    .... I worked hard to attach the electrodes to it.
     
  3. Guest

    Assuming the user picture controls work properly and the image is not
    gray when the color is turned off:

    Could be a worn out picture tube that will no longer properly balance
    or a failure in the video circuitry. You really need to have the video
    output voltages and drive levels checked to confirm that there is no
    failure before cranking on controls.

    In short, the drives control the high level on the tube and the
    background sets the low level.

    If readjusting:

    Depending on the specifics of the model the drives probably need preset
    to mid control for the blue and green to set the base drive levels the
    same as the red.

    Then turn all three background controls all the way back to minimum.

    Apply a black and white gray scale bar pattern on screen. If the set
    has a service switch then it needs to be set to give a single line
    across the screen.

    Turn up the G2/screen voltage until one of the gun colors is clearly
    but slightly visible across the screen. If there is no service switch
    then the 10 IRD gray bar should be used for the background adjustment.

    If it is red or green then the other colors background, red or green,
    needs adjusted to make the line yellow. Then adjust the blue
    background to make the line as close to white or light gray as
    possible.

    Turn off the service switch and look at the lightest color of gray
    before the white. Adjust the blue and green drive to make the
    highlights look as close to gray and white as possible.

    Given the age of the set it is probable that the crt will not track
    properly from low light to high light gray scale. Get it as close as
    possible.

    Otherwise it might be helpful to have a technician do the gray scale
    adjustment that has lots of experience. They will be able to generally
    get it close by eye and fudge the adjustment a little even on a weak
    tube to get a watchable picture.
     
  4. Joust

    Joust Guest

    is there a way to know for sure if the tube is bad?
    can you measure voltages on the guns or use a scope? I've tweaked these
    a lot and got no satisfaction.

    another question. since its the red drive that needs turned up can a
    pot be added presumably in place of some fixed resistors that set the
    red as the ref color.
     
  5. kip

    kip Guest

    Yes to the first question.
    Take the TV to a service shop that has the CRT testing equipment.
    As far as messing with the resistors NO..
    Then you will know for sure and then can get on with your life
    and replace the TV....After all its only an appliance.


    kip
     
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