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Panasonic ct-27g7df .

Discussion in 'Troubleshooting and Repair' started by nath1, Dec 25, 2013.

  1. nath1

    nath1

    1
    0
    Dec 25, 2013
    I need help with this CRT Panasonic model ct27g7df tv,The problem is that any key press bring up the menu display on screen,nothing else work.
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Hi and welcome to Electronics Point :)

    I downloaded the service manual from electrotanya. Here is the section with the front panel pushbuttons:

    [​IMG]

    This set uses a common and simple trick to read the front panel pushbuttons using just one or two pins on the main MCU (microcontroller). A signal marked KEY1 is pulled up to +5V by R032 (10k, 1%) and should sit at +5V when no pushbutton is pressed. The pushbuttons are connected from the 0V rail to KEY1 through a chain of resistors (R033~037). When a pushbutton is pressed, a voltage divider is formed between R032 and one or more resistors in the chain, and this causes a change in the voltage on KEY1 that depends on which button is pressed. The MCU measures the voltage on KEY1 using a simple ADC and calculates which button is being pressed.

    This set also has a signal called KEY2 which is connected to the ACTION button only, and to transistor Q092 and a higher voltage power supply rail. I don't know how this part of the circuit works.

    It's possible that one of the pushbuttons has failed short-circuit, possibly from being pushed too hard. The fault could be R032. There could be a crack in the circuit board caused by pushing a button too hard. There are many possibilities. The next step in diagnosing the problem would be to measure the KEY1 (pin 8) and KEY2 (pin 9) voltages on IC001, the 80-pin microcontroller, and see how they respond to pushbutton presses.

    If you want to continue, I will try to help, but I NEED you to answer ALL OF THESE QUESTIONS.

    You said that pressing ANY button causes the menu to be displayed. Is there any button that is SUPPOSED to bring up the menu?

    What experience with electronics repairs have you had?

    Have you worked on half-live equipment before? Do you know what that means?

    What test equipment do you have? Multimeter? Isolating transformer? Ground fault current interrupter / residual current detector (RCD)?
     

    Attached Files:

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