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TV set won't stay on one channel

Discussion in 'Electronic Repair' started by Matt, Oct 27, 2007.

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  1. Matt

    Matt Guest

    Hi Folks,

    My TV works fine except that it won't stay on the channel it's set to.
    It keeps cycling through the channels as if the channel-up button is
    being pressed. The problem is not in the remote, since it happens when
    the batteries are removed from the remote and the remote is put in a
    different room.

    The model is Panasonic CT-20G21, a 21" box from 1996.

    I have little test equipment beyond a multimeter. I am able to solder,
    and I have some understanding of electronics, but no experience working
    on TVs.

    Please advise.
  2. Meat Plow

    Meat Plow Guest

    Cover the IR window on the tv with black tape and advise.
  3. none

    none Guest

    Just a wild guess: Check the channel-up and channel-down buttons on your
    TV. They should "click" when pressed. If the button is stuck down, or
    the switch below the button is damaged, you probably won't feel that
    "click", or it might have a "mushy" feel.
  4. Matt

    Matt Guest

    Okay, tried that. No difference.
  5. Matt

    Matt Guest

    The buttons are okay. I suspect an electronic defect in the tuner.
  6. Meat Plow

    Meat Plow Guest

    Does the set have an OSD and do the channel numbers change when it changes
    channels on its own?

    If they do not change it /could/ be a problem with the tuner but no

    I'd look more into the device(s) that decode the IR
    and or those that interface the buttons to the sets logic control if the
    OSD changes channels. Without a schematic/service literature this may not
    be something that you can perform due to your limited knowledge.
  7. clifto

    clifto Guest

    As I recall, years back we had a KV25XBR with a shorted channel switch
    that felt just fine mechanically.
  8. This could be caused by what I call "MOSFET lockup". (I've seen things like
    this in other products.)

    With the set turned on, pull out the power plug and let the set sit for
    several minutes. Then see what happens.
  9. JANA

    JANA Guest

    Check the channel up and down switches on the front panel in case one of
    them is making contact. It can also be a fault in the uPC.



    Okay, tried that. No difference.
  10. none

    none Guest

    Such things do occasionally happen. And that is why I used the term:
  11. b

    b Guest

    let's start eliminating the easy stuff. if the IR sensor is covered
    and the set keeps changing, remove the back, slide out the pcb a few
    inches, stay away and power up.Observe. sometimes the plastic keys on
    the set deform and press the microswitches. if this does not cure it,
    desolder the microswitch for ch+ and see what happens.

  12. Ken G.

    Ken G. Guest

    If someone sprayed something on the screen to clean it , or kids with
    something .. it could run down inside and drip on those buttons . Take
    the board out and inspect .
    Take care not to get shocked .
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