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Picture fades out

Discussion in 'Electronic Repair' started by ND, Nov 25, 2003.

  1. ND

    ND Guest

    Hi,
    I have a 27 inch Panasonic, PIP tv(around 9 years old). Here is the problem
    This was some time back, When I turn on the TV, picture comes up but
    in 5-10 seconds slowly fades away till there is blank screen, the sound is
    fine.
    Now if I turn off the TV and turn it back on the picture doesn't come. If I
    keep the TV
    plugged out for a long time and try it again the above behaviour is
    repeated(picture comes up and fades out).
    This has gotten worse and worse, and now when I turn on the TV even after
    keeping it plugged out for a long time, the picture does not come up.
    I dont know much about TVs but I after reading some of the posts on this
    newsgroup, I opened up the TV to check two things, to see if there are bad
    solders at the board that hooks up with CRT and to see if I turn on the TV,
    at the end of CRT if I see orange glows. The solders look ok to me but when the
    TV is on, I dont see any glows in the glass tube at the end of CRT.
    What could be the problem ? Is there anything I can do to repair this TV.
    Thanks in advance for your help.

    -ND
     
  2. Jerry G.

    Jerry G. Guest

    There is a component that has become thermo sensitive with age. When the
    set is cold, it is performing near to spec, and when warm it is changing
    value. Electrolytic capacitors are known for this type of fault.

    By taking readings of the biases to the CRT elements, and of the main power
    supply outputs, a determination of the area of failure may be easily
    determined. Also, looking at the amplitude of the video signal to the CRT
    elements from the video amps (RGB), may also give some clue. Once you know
    the area that is causing the failure, then you can go on to troubleshooting
    for the defective parts.

    Once you know where you are going, you can use some freeze spray and a heat
    gun to cool and reheat the suspect components to test them. When you get
    the right one, you will be able to make the effect by cooling and heating
    the parts. It is very possible that you will find a number of parts that
    are defecting with this approach.

    --

    Greetings,

    Jerry Greenberg GLG Technologies GLG
    =========================================
    WebPage http://www.zoom-one.com
    Electronics http://www.zoom-one.com/electron.htm
    =========================================


    Hi,
    I have a 27 inch Panasonic, PIP tv(around 9 years old). Here is the problem
    This was some time back, When I turn on the TV, picture comes up but
    in 5-10 seconds slowly fades away till there is blank screen, the sound is
    fine.
    Now if I turn off the TV and turn it back on the picture doesn't come. If I
    keep the TV
    plugged out for a long time and try it again the above behaviour is
    repeated(picture comes up and fades out).
    This has gotten worse and worse, and now when I turn on the TV even after
    keeping it plugged out for a long time, the picture does not come up.
    I dont know much about TVs but I after reading some of the posts on this
    newsgroup, I opened up the TV to check two things, to see if there are bad
    solders at the board that hooks up with CRT and to see if I turn on the TV,
    at the end of CRT if I see orange glows. The solders look ok to me but when
    the
    TV is on, I dont see any glows in the glass tube at the end of CRT.
    What could be the problem ? Is there anything I can do to repair this TV.
    Thanks in advance for your help.

    -ND
     
  3. James Sweet

    James Sweet Guest

    Sounds like the CRT heater is definitly losing power. The problem is
    probably solder joints, but if those on the neck board are fine they're
    likely on the main board, look in the vicinity of the flyback transformer,
    or better yet, trace the wiring down to the main board. On a 13" TV/VCR
    combo I fixed that had been dropped, I had no heater power, but the main
    board was very difficult to remove to further inspect so I simply wrapped 2
    turns of wire around the flyback core and soldered those to the heater pins
    on the CRT board, this added secondary was just right to power the heater.
    Careful not to go overboard if you try this, 2 turns is usually plenty, at
    most 3, you can best judge the voltage by inspecting the glow in the tube.
     
  4. If the picture fades out in 10 to 20 seconds, it still could be a bad
    solder connection to the CRT heater - what is supposed glow orange.
    The bad soldering is probably on the CRT neck board.

    More info at the site below, especially on SAFETY!

    --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: The email address in this message header may no longer work. To
    contact me, please use the Feedback Form at repairfaq.org. Thanks.
     
  5. Pussynuts

    Pussynuts Guest

    Check the filtering capacitor in the g2 circuit on the neckboard.Common
    fault.
    Cheers
    Joe
     
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