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Viewsonic VX2235WM-3 problems

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    #1

    Viewsonic VX2235WM-3 problems

    Hi,
    I am trying to diagnose an issue with the above monitor.
    Initially, I assumed that it was a PSU issue, but I'm not so sure.
    OK, here are the symptoms:

    Powering on the monitor, the backlight comes on, but there is no display on the panel. The power light is illuminated Blue.
    After about 3 seconds, the backlight goes off and the the power light goes Amber.
    I cannot get it to do anything with the buttons with either the blue or amber lights illuminated.

    If I plug in a VGA source, then the panel stays on indefinitely, blue light + backlight.
    I can manipulate the power LED and backlight status by plugging the VGA connection in and out so it is not completely dead and is reacting to stimulus.

    So, it sounded like the classic issue, power on, then to black after a few seconds which suggests PSU voltage issues.

    I downloaded a service manual and had a look at the schematics etc
    I have checked voltages with a meter from the PSU and there is 5V output to the logic board. The PSU is also generating 24V measured at the L803 link, although the logic board does not seem to require it.

    I measured the outputs of the 3.3V and 1.8V regulators on the logic board and it seems good.

    I put an analogue scope on all the voltages and they seem nice and steady, not flapping around all over the place.

    Since the RTD2553V LCD controller seems to be doing something (maybe, the display does not go off when I plug in an active VGA connection to a running PC), I can only assume that there is something amiss with the microcontroller.

    And this is where I start to flounder somewhat.

    Any ideas where I should look now? I did see something about EPROM going bad somewhere but couldn't find any details.

    I will post some board pictures.
    Last edited by skelband; 02-15-2021, 03:12 PM.
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    #2
    Re: Viewsonic VX2235WM-3 problems

    I also check the reset signal on the logic board. Jumps up briefly on power, drops to ground quickly after. Cap/diodes seem good.

    If people think that there is still some merit in recapping the PSU (perhaps the levels are not as stable as my old analog scope seems to think) I am happy to do that and come back to it. There is no obvious cap deterioration although of course there isn't always a physical sign.

    Also, confirmed that pin 9 of the power cable bound for the main logic board, at the PSU side, is not connected. It carries the 24V power, so that confirms that it is not required for the logic board.
    Attached Files
    Last edited by skelband; 02-15-2021, 04:25 PM.

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      #3
      Re: Viewsonic VX2235WM-3 problems

      Since you have a scope, check if you have video signals on the lvds cable going to the panel, also check if you have +5v going to the panel (P104 pins 28,29,30). Q103 is the mosfet that controls the panel voltage, Source is +5v Drain connects to the panel.

      You need to have signal going to the monitor or it will likely go into standby.
      If the backlight is working and stays on I suspect the power supply is ok.
      Last edited by R_J; 02-15-2021, 06:43 PM.

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        #4
        Re: Viewsonic VX2235WM-3 problems

        Thanks for the suggestions.
        I can verify that 5V is present on the P104 connector and if I put a VGA signal on the VGA port from a PC, I can see activity on the LCD lines lines on that connector.

        When I look at the panel though, I only see the backlight and no display content.

        It is very strange.

        My scope is very old and not really intended for looking at this kind of thing. It looks like the signals are offset by about 1.5V but oscillating by about 0.25V. Take that with a pinch of salt however since it is well out of calibration.

        I also checked the ground connections to P104.
        Last edited by skelband; 02-17-2021, 12:27 AM.

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          #5
          Re: Viewsonic VX2235WM-3 problems

          The scope doesn't need to be that fancy, if you have what looks like video on the lvds and there is 5 volts, I suspect there is a problem on the t-con board, that's the board that drives the panel

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            #6
            Re: Viewsonic VX2235WM-3 problems

            Originally posted by R_J View Post
            The scope doesn't need to be that fancy, if you have what looks like video on the lvds and there is 5 volts, I suspect there is a problem on the t-con board, that's the board that drives the panel
            OK, that makes sense.
            I'll have to dig further into the panel to find that.
            What an interesting adventure!

            Comment

              #7
              Re: Viewsonic VX2235WM-3 problems

              I managed to strip it enough to get to the TCON board but I couldn't find anything there. Nothing obvious. There look to be a couple of voltage regulators on there but I could not find anything amiss.

              I think I have spent more than is reasonable on this project so it is going to recycling. Thanks for the help though!

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