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    #1

    Dell 1704FPT - Flickering and hissing

    I have a Dell 1704FPT 17" LCD Monitor that I purchased new in 2005.

    Yesterday morning it started flickering (as if one of the two backlight lamps was switching on and off) and it was almost making a noticeable hissing noise.

    Having ordered a replacement monitor, I thought it would be interesting to disassemble this one to see if I could fix the problem, as the monitor is otherwise in good working order.

    Having carefully taken the monitor apart, I carefully reconnected the power supply and control boards, and powered up the monitor. The flickering was still present, as was the hissing.

    From careful inspection and listening, the hissing seems to be coming from one of the transformers, in the inverter portion of the power supply board.

    In the photo's attached, it's the transformer that is at the same end of the board as the mains connector.

    Also of note, the sister transformer at the other end of the board is, when powered, cold to the touch. The hissing transformer seems to be getting quite warm to the touch.

    If the monitor is put into standby (powered, but with backlights off) the hissing stops.

    Is it the transformer that is faulty, and can this be repaired easily?



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    #2
    Re: Dell 1704FPT - Flickering and hissing

    In the future please use managed attachments to post your photos
    Figure out a way to install the top CCFL bulb connectors into the bottom inverter connectors,and bottom bulbs in top inverter connectors.
    Dose the noisy transformer change positions?
    Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

    Comment

      #3
      Re: Dell 1704FPT - Flickering and hissing

      To add to alexanna's suggestion, if the problem stays with this transformer, the transformer cannot be repaired, it must be replaced. This is quite easy to do if you can find a replacement. In many case, this requires nothing more than an eBay search for the number stamped on the transformer.

      If the problem moves to the other transformer, you have either a bad CCFL, or CCFL wiring.

      PlainBill
      For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

      Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

      Comment

        #4
        Re: Dell 1704FPT - Flickering and hissing

        Originally posted by alexanna View Post
        Figure out a way to install the top CCFL bulb connectors into the bottom inverter connectors,and bottom bulbs in top inverter connectors.
        Dose the noisy transformer change positions?
        The leads from the lamps are only just long enough to go to their current locations. I cannot see any easy method to swap them round.

        Originally posted by PlainBill View Post
        To add to alexanna's suggestion, if the problem stays with this transformer, the transformer cannot be repaired, it must be replaced. This is quite easy to do if you can find a replacement. In many case, this requires nothing more than an eBay search for the number stamped on the transformer.

        If the problem moves to the other transformer, you have either a bad CCFL, or CCFL wiring.

        PlainBill
        Yes, I realise the transformer itself cannot be repaired. I was refering to the monitor in general.

        If I cannot swap the lamps round, would disconnecting the lamp from the faulty transformer help? With the lamp disconnected, would the hissing continue if the transformer is faulty?

        Comment

          #5
          Re: Dell 1704FPT - Flickering and hissing

          You can swap the CCFLS,Toasty said it best flip the board over.
          I use a piece of cardboard to insulate the inverter/power supply so that nothing shorts to ground.
          You don't need to have the flat LDVS ribbon hooked up to the panel; the panel gets its voltage through the ribbon so insulate it also.
          The noise you are hearing is most likely caused by the transformer or a CCFL,so that part of the circuit should all be hooked up.
          Give the CCFL connectors a good Eyeball also for damage.
          Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

          Comment

            #6
            Re: Dell 1704FPT - Flickering and hissing

            Originally posted by alexanna View Post
            You don't need to have the flat LDVS ribbon hooked up to the panel;
            Which cable is this? The one with many many tiny wires, that goes between the LCD and the main control board?



            Originally posted by alexanna View Post
            Give the CCFL connectors a good Eyeball also for damage.
            Visually, they look fine.

            Comment

              #7
              Re: Dell 1704FPT - Flickering and hissing

              Yes that's the one,looks like it's already disconected.
              Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

              Comment

                #8
                Re: Dell 1704FPT - Flickering and hissing

                I have a 1703 on my waiting for parts shelf, that also needs a transformer.
                Haven't tried too hard to find one yet, but I think my initial search wasn't too successful.
                36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

                Comment

                  #9
                  Re: Dell 1704FPT - Flickering and hissing

                  Originally posted by alexanna View Post
                  Yes that's the one,looks like it's already disconected.
                  No, the cable is just tucked down behind the wooden block the board is sat on.

                  Originally posted by smason View Post
                  I have a 1703 on my waiting for parts shelf, that also needs a transformer.
                  Haven't tried too hard to find one yet, but I think my initial search wasn't too successful.
                  I've come to the same conclusion regarding getting a replacement transformer.

                  What I'm considering doing is using the perfectly good panel to build a DIY video projector.

                  I noticed the cable, from the power supply to the control board, has a wire marked BACKLIGHT_EN. I suspect this is a simple logic level signal to turn the inverters on/off (such as when the monitor goes into standby when no input signal detected), then it shouldnt be a problem to disable them permenantly.

                  Comment

                    #10
                    Re: Dell 1704FPT - Flickering and hissing

                    Originally posted by davepusey View Post
                    No, the cable is just tucked down behind the wooden block the board is sat on.



                    I've come to the same conclusion regarding getting a replacement transformer.

                    What I'm considering doing is using the perfectly good panel to build a DIY video projector.

                    I noticed the cable, from the power supply to the control board, has a wire marked BACKLIGHT_EN. I suspect this is a simple logic level signal to turn the inverters on/off (such as when the monitor goes into standby when no input signal detected), then it shouldnt be a problem to disable them permenantly.
                    Perhaps you and smason could make arrangements to transfer a good transformer from one to the other. The one can have another working monitor and the other a DIY video projector.

                    PlainBill
                    For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                    Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                    Comment

                      #11
                      Re: Dell 1704FPT - Flickering and hissing

                      Originally posted by PlainBill View Post
                      Perhaps you and smason could make arrangements to transfer a good transformer from one to the other. The one can have another working monitor and the other a DIY video projector.

                      PlainBill
                      And excelent idea, assuming the transformers are the same between the 1703 and the 1704FPT.

                      I did find a refurbished board online for £30, but as my replacement monitor only cost £69 it wasn't worth it in my opinion... http://www.codemicro.com/store/produ...efurbished.php

                      Comment

                        #12
                        Re: Dell 1704FPT - Flickering and hissing

                        On some monitors the Dell 1704FPT and the Dell 1905FP use the same board. Some of these boards have a manufacturer's defect where they used a 22uF 50v cap next to that inverter transformer, when it should have been a 2.2uF 50v.
                        I have a previous post on this. https://www.badcaps.net/forum/showpo...8&postcount=15

                        Comment

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