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Samsung UE65C8790 Trouble

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    #1

    Samsung UE65C8790 Trouble

    Hi!
    I have a Samsung UE65C8790 that has suddenly gaven up.
    As soon as I try to turn on the TV via the remote control, the TV flashes 4x and then the relay clicks again and the TV flashes 4x again (nearly every 8 seconds). This repeats endlessly until I unplug it. The screen stays black throughout (no backlight either).

    First I tested the backlight LEDs = working

    According to the service manual (page 92 or 4-32) PIN 16 and 18 should be bridged at the connector CNM801 to test the function of the power supply. I have done this. = Backlight turns on. The power supply seems to be ok.
    When I test it like this, there is a voltage of about 39V at the LEDs.
    If I switch on the TV normally (it does not turn on), then only a voltage up to about 33V is generated.

    Page 87 (or 4-8) describes the procedure for No Power. All components I found also had the expected voltage present.
    But I can't find IC206 on my mainboard. The smallest number for components was something around 400.

    I find unfortunately also no executed contacts with which one could reset an EPROM.

    Status LED on the TV responds to the remote control.
    Of course, I have already tried all the shortcuts for the service menu.

    Mainboard is BN94-03469D (on the same label it says UE65C8705XSXXE)
    Power supply is BN44-00378A


    Is there another manual for it?
    I can hardly find anything about the device. Maybe already too old?
    Is this already a bootloop or should I still focus on the fact that the backlight is not turned on?
    I have already downloaded the firmware from Samsung.com and put it on a stick, but as expected, nothing happens.

    Service manual i found is attached.
    Attached Files
    Tags: None
    #2
    Re: Samsung UE65C8790 Trouble

    I ordered a used (but working according to the seller) power supply and will put it in this week to rule out the power supply.

    Comment

      #3
      Re: Samsung UE65C8790 Trouble

      The new PSU still has not been delivered and I am impatient
      There seems to be no communication from the mainboard to the LED driver board.
      At the connector of the power supply I measured the SCL and SDA lines and it is 3,3V (measured with multimeter).
      With the oscilloscope I expected to see the clock at least on SCL but there is nothing oscillating.
      Even with the smallest possible setting on the oscilloscope (10ns division). I can't see anything oscillating.
      The traces on the mainboard of the connector go over a resistor with 0 Ohm each under the IC8001.

      While following the traces I "accidentally" found the eeprom (IC8002).
      With multimeter its also 3,3V but here I could detect an oscillation at the SCL and SDA at each "restart" for about 2-3 seconds. The traces also go through a resistor with 0 Ohm each under the IC8001. So i assume the IC8001 is up and running.

      Pins (14,13,11,10,9) named Serial are all near zero V. Nothing to see on oscilloskope.

      Any suggestions other than waiting for the new power supply?
      Anything that I can measure?
      Attached Files

      Comment

        #4
        Re: Samsung UE65C8790 Trouble

        The PSU was not the solution.

        So a guy from a German forum told me I could use the mainboard from a UE40S870 and it's visually the same mainboard.
        I bought one and installed it. I hear a startup sound when I turn it on and the backlight comes on (and stays on).
        Unfortunately, I still don't see a picture.
        Can someone guide me blindly through the menu so I can do Panel Auto setting? Or is there another way to force the board to do a panel scan?

        Comment

          #5
          Re: Samsung UE65C8790 Trouble

          Also carefully compare these position resistors and compare both boards, how they are installed, they can be in other places, on the other hand ...
          Attached Files

          Comment

            #6
            Re: Samsung UE65C8790 Trouble

            On both boards the resistors are on the same places.
            Should I check the values? Could do it later today

            Comment

              #7
              Re: Samsung UE65C8790 Trouble

              The values there should be the same, but their permutations matter, they can be in other places.

              Comment

                #8
                Re: Samsung UE65C8790 Trouble

                Is the T-CON powered from the motherboard 12v?

                Comment

                  #9
                  Re: Samsung UE65C8790 Trouble

                  Thank you from the bottom of my heart.
                  Tried to measure 12V on tcon and could not find 12V.
                  So I double checked all connectors and the ribbon was not fully pushed inside the mainboard.
                  Everything looks fine now.
                  Nice picture is there again.

                  Comment

                    #10
                    Re: Samsung UE65C8790 Trouble

                    It's good that it was so easy.

                    Comment

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