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    Help converting an old monitor into a lightbox

    Hi,

    This is my first post here so apologies if this is in the wrong place, or even the wrong forum! Looking around i can tell there is a lot of knowledge here on the subject.

    I managed to procure an old monitor from work which I'm trying to convert into a light box for drawing. I've found threads and videos of this being done using a separate power supply to feed the inverter boards, but I'm hoping that i can use the monitors own power supply to do this.

    The monitor is an old one with two cfl's.

    I've stripped down the monitor to the diffuser layer already and it now functions as a light box, but only for a few seconds at a time. I assume that this a power saving feature, since there is no signal going to the monitor, it turns itself off.

    I tried disconnecting the controller board, but the backlight will not turn on without it.

    The power supply is a benq 4H L2E02 A35. Does anyone know if there is a trace i can cut/component i can remove/signal i can short to ground, which will isolate the output to the inverters?

    All other suggestions welcome, attached is an image of the guts of the monitor in it's current state.

    Thanks all in advance!
    Attached Files

    #2
    Re: Help converting an old monitor into a lightbox

    look at the board connectors for one marked bl on

    Comment


      #3
      Re: Help converting an old monitor into a lightbox

      Hi Pete, thanks for the reply!

      I'm looking at the bottom of the power board now and no such luck, the pinout isn't labeled. Would this be on the ten pin cable between the power supply board and the controller? Is there a standard wire colour?

      Comment


        #4
        Re: Help converting an old monitor into a lightbox

        I found this schematic for a similar (I think) power supply and located the bl on pin.

        http://www.eserviceinfo.com/download...BenQ_Q7C4.html

        What should I do with it?

        Comment


          #5
          Re: Help converting an old monitor into a lightbox

          no idea about wire colours .
          i think the thing would be to short bl on to 0v gnd using a 1k resistor .
          please dont try this without confirmation from someone more knowledgeable
          Last edited by petehall347; 03-19-2017, 03:28 PM.

          Comment


            #6
            Re: Help converting an old monitor into a lightbox

            Best thing to do is to provide really good clear straight shot pictures of the top side and the bottom side of the power supply/inverter board so I can trace out the connections.
            Never stop learning
            Basic LCD TV and Monitor troubleshooting guides.
            http://www.badcaps.net/forum/showthr...956#post305956

            Voltage Regulator (LDO) testing:
            http://www.badcaps.net/forum/showthr...999#post300999

            Inverter testing using old CFL:
            http://www.badcaps.net/forum/showthr...er+testing+cfl

            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
            http://s807.photobucket.com/user/budm/library/

            TV Factory reset codes listing:
            http://www.badcaps.net/forum/showthread.php?t=24809

            Comment


              #7
              Re: Help converting an old monitor into a lightbox

              What model LCD monitor is this? If you can tell us the (bottom-side) BL IC's part number. i.e OZ9938GN or TL1451
              Confirm the monitor model number-
              I see PSU board has two control signals to satisfy:
              CN701 Pin 1 (blk) is "BRT_ADJ"
              CN701 Pin 2 (brn) is "BL_ON" or "BRT_ON"

              Looks like you need to have two signals right to get it to light up.

              P.S. These PSU boards do have capacitor issues, so make sure they are not bloated.

              Comment


                #8
                Re: Help converting an old monitor into a lightbox

                Hi all,

                Sorry for the delay, i didn't get a chance to take clear photos until this evening, i hope that these will help.





                The model of monitor escapes me i'm afraid. I stripped this down during my lunchbreak at work, and all the plastics, stand etc, went in the skip when we moved office.

                This is the ic on the bottom of the psu board: http://www.datasheetcafe.com/0z9938g...df-controller/

                I'll have a dig into the datasheet now, but unfortunately, my electronics knowledge is *ahem* "pre-transistor"

                Cheers!

                Edit: I can see now that the IC doesn't match the schematic i previously shared, sorry about the red herring!
                Attached Files
                Last edited by Yangs; 03-21-2017, 04:35 PM.

                Comment


                  #9
                  Re: Help converting an old monitor into a lightbox

                  looks like you will need a new set of electrolytic capacitors as they are bulging on top .

                  Comment


                    #10
                    Re: Help converting an old monitor into a lightbox

                    I agree - most of the electrolytic caps have a bulged top and need to be replaced first, probably why the monitor was tossed aside. I see a poor solder joint on C709 (near CN701).

                    I could not find a schematic of the 4H.L2E02.A35 BenQ power supply board. It would be in the LCD monitor service manual. Closest is Russian members-only site: http://monitor.net.ru/forum/benq-ser...anual-205.html
                    It seems to be used in Q9W5-FP71G+, (not Q7T4-FP71G), Q9T4-FP91G+

                    The PSU board schematic helps tell us how to spoof the backlight on/off and brightness signals.
                    I can guess what to do from the OZ9938GN datasheet:
                    Applying over +2V to "BL_ON" turns on the backlight. I would tie it to +3.3V or +5V.
                    The DIM pin <0.1V 0% brightness dark panel, 0.2V is min. brightness, >1.5V max. brightness.

                    BUT you don't what extra electronics is on the PSU board, so this could be wrong.

                    Comment


                      #11
                      Re: Help converting an old monitor into a lightbox

                      Tracing out the board, it looks like pin 1 (Black wire) is for the Dimming, pin 2 (Brown wire) is the BL-ON.
                      So to safely turn on the backlights circuit is to use 1K 1/4W resistor between pin 2 and the 5V pin, you will not have the connector connected to the logic board otherwise it will not allow the line to go high.
                      The dimming control may be PWM not DC control so if he backlights do not come on, then you will have to use another 1K resistor between pin 1 and the 5V, this give max brightness.
                      But before doing the mod, you will need to replace the caps on the board first.
                      Last edited by budm; 03-21-2017, 10:35 PM.
                      Never stop learning
                      Basic LCD TV and Monitor troubleshooting guides.
                      http://www.badcaps.net/forum/showthr...956#post305956

                      Voltage Regulator (LDO) testing:
                      http://www.badcaps.net/forum/showthr...999#post300999

                      Inverter testing using old CFL:
                      http://www.badcaps.net/forum/showthr...er+testing+cfl

                      Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                      http://s807.photobucket.com/user/budm/library/

                      TV Factory reset codes listing:
                      http://www.badcaps.net/forum/showthread.php?t=24809

                      Comment

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