LCD 31MU97Z displays random lines randomly

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  • Vspeed
    Senior Member
    • May 2022
    • 53
    • Portugal
    #1

    LCD 31MU97Z displays random lines randomly

    I have this monitor which had the known issue with the corrupted flash. That is solved, now, after some time it started to cut the image from time to time and just display grayish random vertical lines. After some minutes the image usually comes back, until it does the same again.

    I took it apart and the only think that I noticed was ZD1 protection diode on the TCON board reaching 90ºC when it's showing this erratic behavior. I measured the voltage on the fuse right beside it, and is measuring 15.3V (under load). Without the TCON board connected, the connector measures 18.3V.
    The diode has 6U written on it. Do you think the diode is misbehaving or is the voltage somehow not stable?
    Attached Files
    Last edited by Vspeed; 01-22-2023, 02:36 PM.
    Tags: None
    • lotas
      Badcaps Legend
      • Jan 2016
      • 4522
      • Russia
      #2
      Re: LCD 31MU97Z displays random lines randomly

      "6U" (SD12) is a 12 volt suppressor, you have a very high power supply to the panel, it should be 10 volts.
      Attached Files

        Comment

        • Vspeed
          Senior Member
          • May 2022
          • 53
          • Portugal
          #3
          Re: LCD 31MU97Z displays random lines randomly

          Could MP2315GJ be shorted or defective?
          I need to try and check it.

            Comment

            • lotas
              Badcaps Legend
              • Jan 2016
              • 4522
              • Russia
              #4
              Re: LCD 31MU97Z displays random lines randomly

              Yes, it could break through the input with the output (internal Mosfet), check the setting divider for the output voltage is R745, R746, R747 and the recommended resistor R726 at 62kOm.
              Attached Files

                Comment

                • Vspeed
                  Senior Member
                  • May 2022
                  • 53
                  • Portugal
                  #5
                  Re: LCD 31MU97Z displays random lines randomly

                  All the resistors match the schematic. Also, IN and SW are not shorted, they read 0.567V in diode mode (black probe IN, red probe SW). The same between these and ground (red probe on ground)
                  I took measurements for other MP2315GJ around and they read more or less the same values...

                    Comment

                    • lotas
                      Badcaps Legend
                      • Jan 2016
                      • 4522
                      • Russia
                      #6
                      Re: LCD 31MU97Z displays random lines randomly

                      Replace with a new MP2315GJ, the input and output voltage must not be the same.

                        Comment

                        • Vspeed
                          Senior Member
                          • May 2022
                          • 53
                          • Portugal
                          #7
                          Re: LCD 31MU97Z displays random lines randomly

                          Found the issue. R746 was detached from the board on one of the legs. screen working fine again.
                          Thank you.

                            Comment

                            • lotas
                              Badcaps Legend
                              • Jan 2016
                              • 4522
                              • Russia
                              #8
                              Re: LCD 31MU97Z displays random lines randomly

                              Originally posted by Vspeed
                              Found the issue. R746 was detached from the board on one of the legs. screen working fine again.
                              Thank you.
                              Yes, it is these resistors (R745, R746, R747) that set the output voltage to 10v, congratulations.

                                Comment

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