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LCD 31MU97Z displays random lines randomly

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    #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
    #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

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      #3
      Re: LCD 31MU97Z displays random lines randomly

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

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        #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

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          #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...

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            #6
            Re: LCD 31MU97Z displays random lines randomly

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

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              #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.

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                #8
                Re: LCD 31MU97Z displays random lines randomly

                Originally posted by Vspeed View Post
                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.

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