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ASUS VH238T blank screen with backlight

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    #1

    ASUS VH238T blank screen with backlight

    Hello,

    I am having a problem with a ASUS VH238T.
    The monitor started by just going blank, but the integrated speakers, and the backlight worked. The OSD didn't pop up, neither did the messages of DVI No Signal, nor the Asus logo.
    Turning off the monitor, and turning it back on made no difference. But leaving the monitor off for a few hours returned the monitor back to normal. The problem will eventually return after a couple of hours.

    Today, it started exhibiting another symptom: the display started showing a white image, that didn't take the whole screen. Then it went back to being blank, I turned off and back on, the ASUS logo showed up, and the screen slowly turned white, and then back to blank.






    I disassembled the monitor, and could not see any obvious damage to its components.
    Thy shall measure volts, but I am not sure where to start measuring, even more because I don't know what the voltages are supposed to be, there is no printing on the boards indicating what the voltages would be.

    I am also suspecting this might be a bad panel, and nothing to do with the PCBs.
    What do you guys advise me to do next?
    Attached Files
    Tags: None
    #2
    Re: ASUS VH238T blank screen with backlight

    Looks like C830 & C816 on the power board are bulging?
    "The one who says it cannot be done should never interrupt the one who is doing it."

    Comment

      #3
      Re: ASUS VH238T blank screen with backlight

      It's a picture "artifact"
      In reality they look normal. Can't spot any bulged caps, or that look like they leaked or vented.

      I noticed this flex cable, connects ot the display's PCB. I wanted to make sure it's all the way in, but I am having one of those newbie moments where I don't know how to remove it, and I am scared I will break it.

      Attached Files
      Last edited by Spoonicks; 07-04-2023, 04:23 PM.

      Comment

        #4
        Re: ASUS VH238T blank screen with backlight

        The flex is well connected, I managed to remove it, and reconnect it.

        Been testing the flex cable, ground pins are: 7, 14, 17, 24.
        The ground pins are the same on both boards connect by the flex cable, so I don't see any obvious shorts to ground.
        Attached Files

        Comment

          #5
          Re: ASUS VH238T blank screen with backlight

          The problem seems to be "intermittent", so you shouldn't see any obvious shorts to ground.

          My bet would be either on the small electrolytic caps on the logic board (change all of them with good quality low ESR Japanese caps) or possibly a diode or ceramic cap on the T-con board going "wonky". Could also be a linear reg on the logic board or the T-con going out, so check the input and output voltages on all of these. Particularly, see if you can measure the voltages when the monitor appears to be working OK and when it's not.

          The two output caps Per mentioned could also be an issue, even if they don't appear to be bulging... but that wouldn't explain why the monitor looses picture when it's been running for a while, as heat decreases the ESR of caps. This also sort of rules out the small electrolytic caps on the logic board... but I always find them to be more of a culprit when the issue appears to be signal-related, like in this case.

          Comment

            #6
            Re: ASUS VH238T blank screen with backlight

            I will look into replacing the caps.

            Now that I have the monitor apart, I didn't manage to have the issue come back. Before it would come back consistently, after being on for a while.
            Now, it has been 24 hours, and no issues

            The only difference with it being apart, aside from being some sort of bad connection that got fixed, is that the chassis ground is interrupted. Since I have the boards out of the metal casing, they are not grounded with that chassis. Don't know if this is important and would indicate some sort of failure. They are however grounded through the vga cable, and the power supply is grounded through the earth pin.

            Comment

              #7
              Re: ASUS VH238T blank screen with backlight

              In the picture you posted it looks like a T-Con problem so it might well have been a bad connection in its cable if it is working now.
              "The one who says it cannot be done should never interrupt the one who is doing it."

              Comment

                #8
                Re: ASUS VH238T blank screen with backlight

                EDIT: forget about this post. On closer look I could see it was because of the Microsoft windows wallpaper mosaic thing


                It just now started showing a vertical line.

                It worked fine for almost 2 days.
                Is this likely a tcon issue? Or a panel issue?
                Attached Files
                Last edited by Spoonicks; 07-06-2023, 08:50 AM.

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