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    Dell U2713Hb No Display

    Hi all, I've recently got a hold of a broken Dell U2713Hb monitor and am trying to diagnose the issue and fix it. Unfortunately it's just outside of it's warranty.

    The symptoms are that when the power button is pressed, the power light comes on, but there is no display (no display and no backlight). When the other touch buttons are pressed, they all light up and stay lit up until the monitor is powered off.
    I have been told by the previous owner that the USB ports on the side were used to charge a mobile phone daily. I checked out the USB board and it does look to have some damaged capacitors, however the monitor still behaves the same with this board disconnected.

    P.S. I'm quite new to this, so apologies if the photos aren't good enough. I can take some more though if it helps.

    The boards also come mounted upside down inside some sort of metal cage - what is the best way to power these on to probe them. I was thinking of connecting all ground screws back to the first power boards ground connection - would that do the job?

    I would greatly appreciate any help or advice anyone can give.

    Thanks
    Jayden
    Attached Files
    Last edited by drjaydenm; 08-25-2018, 07:28 AM.

    #2
    Re: Dell U2713Hb No Display

    I forgot to mention what I have tried so far:
    • Re-seating all connectors and reassembling - no difference
    • Powering on without the USB board - also no difference
    • Testing ESR for electrolytics using the Blue ESR meter in-circuit. There were no outstanding ESR values - even on the suspect USB caps
    • The 250V fuse is OK. The 3A fuse on the logic board is also OK
    Last edited by drjaydenm; 08-25-2018, 07:42 AM.

    Comment


      #3
      Re: Dell U2713Hb No Display

      Missing pictures of LCD panel to see how the backlights' cable connected to which board.
      Is this the power supply LED driver with the connector on the left of the board that goes to the LCD panel?
      https://www.badcaps.net/forum/attach...2&d=1535203411
      If it is then you need to check the Voltage between the two legs of that brown lytics cap laying on its side next to the TOROID inductor when monitor is turned on.
      Last edited by budm; 08-28-2018, 09:32 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


        #4
        Re: Dell U2713Hb No Display

        Thanks for the guidance. I've checked the voltage of that brown cap and it is sitting at 33.3V - even when the monitor has just been plugged in without the power button being pressed.

        However whilst doing that, I noticed the power LED doesn't light up after pressing the power button - but the other touch buttons all light up. I checked the buttons ribbon cable was seated correctly and can see 0R over the two power wires on the ribbon when the button is held in - so I would think it should be sending the signal to turn on.

        Whilst I had it running, I also checked the logic board connection and can see 12.6V across all 4 red wires and 0 on everything else.

        Here's some labelled diagrams which will hopefully help
        Attached Files

        Comment


          #5
          Re: Dell U2713Hb No Display

          Originally posted by drjaydenm View Post
          Thanks for the guidance. I've checked the voltage of that brown cap and it is sitting at 33.3V - even when the monitor has just been plugged in without the power button being pressed.

          However whilst doing that, I noticed the power LED doesn't light up after pressing the power button - but the other touch buttons all light up. I checked the buttons ribbon cable was seated correctly and can see 0R over the two power wires on the ribbon when the button is held in - so I would think it should be sending the signal to turn on.

          Whilst I had it running, I also checked the logic board connection and can see 12.6V across all 4 red wires and 0 on everything else.

          Here's some labelled diagrams which will hopefully help
          1) "I noticed the power LED doesn't light up after pressing the power button - but the other touch buttons all light up." So if you toggle the power switch, do other touch buttons' light go on and off when power switch toggle?
          2) 'I've checked the voltage of that brown cap and it is sitting at 33.3V' So the LED driver power supply does have 33V feeding the bosst converter circuit, the LED panel has six LED strings so not likely that all six are dead at the same time, so for the backlights not to even flash on for seconds it mean something common has gone wrong, it can be that the BL-On signal from the logic board is not present, or the Boost converter is not working, etc.
          3) This unit will require in-depth troubleshooting down to component level but without the schematic it will be time consuming. How much time are you willing to spend on this, hours, days, weeks?
          4) Your level skill?
          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


            #6
            Re: Dell U2713Hb No Display

            Originally posted by budm View Post
            1) "I noticed the power LED doesn't light up after pressing the power button - but the other touch buttons all light up." So if you toggle the power switch, do other touch buttons' light go on and off when power switch toggle?
            2) 'I've checked the voltage of that brown cap and it is sitting at 33.3V' So the LED driver power supply does have 33V feeding the bosst converter circuit, the LED panel has six LED strings so not likely that all six are dead at the same time, so for the backlights not to even flash on for seconds it mean something common has gone wrong, it can be that the BL-On signal from the logic board is not present, or the Boost converter is not working, etc.
            3) This unit will require in-depth troubleshooting down to component level but without the schematic it will be time consuming. How much time are you willing to spend on this, hours, days, weeks?
            4) Your level skill?
            So if you toggle the power switch, do other touch buttons' light go on and off when power switch toggle?
            The touch buttons light up as soon as the monitor is plugged in and you touch one of them - irregardless of the power button. Pressing the power button then has no effect - the buttons stay lit up.

            'it can be that the BL-On signal from the logic board is not present, or the Boost converter is not working, etc.'
            How do I go about diagnosing the BL-On signal? Which wire would that be sent across to the power supply?

            How much time are you willing to spend on this, hours, days, weeks? Your level skill?
            I'm only starting out with diagnosing broken electronics, but have done a fair bit of electronics with breadboard and arduino projects. I am willing to spend quite a lot of time on this in the pursuit of learning - I just need a little guidance until I get the ropes I've also gotten hold of an oscilloscope if that helps at all.

            At this stage, what's your advice on proceeding?
            I'll also upload a video a little later showing what the monitor buttons currently do when powered on.

            Comment


              #7
              Re: Dell U2713Hb No Display

              Sine there is no label for each pin of the connector it will be a lot of probings.
              Hook everything back up but you can leave the LCD panel disconnected for now, then start checking DCV on each pin of that connector of the power supply that goes to the main board: https://www.badcaps.net/forum/attach...2&d=1535543074
              Start by taking the Voltage readings when monitor is plug in and when the power switch is activated, we are looking for Voltage changes.
              Also get the P/N of the IC (the large one with many many pins on it) in that LED power supply section.
              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


                #8
                Re: Dell U2713Hb No Display

                I am seeing 12.6Vdc on all four red cables in the main board connector. The 2 black and 2 brown cables are both grounded. The other 4 coloured cables all show 0Vdc. Is it normal that all four red cables would be live without the power button being pressed?

                Comment


                  #9
                  Re: Dell U2713Hb No Display

                  It is an always on power supply to keep the logic board active.
                  So those 4 cables with 0V readings should be the command signal lines that the main board sends the signals to the power supply/LED driver board.
                  So it looks like the main board is not sending the signal at all.
                  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


                    #10
                    Re: Dell U2713Hb No Display

                    After more checks on the LED back light, I've probed each pin and I get the following voltages on the connector:
                    1. 0V
                    2. 0V
                    3. 33.1V
                    4. 33.1V
                    5. 0V
                    6. 0V
                    7. 0V
                    8. 0V
                    9. 33.1V
                    10. 33.1V
                    11. 0V
                    12. 0V


                    I've found the datasheet for this model of panel https://www.dropbox.com/s/qvb1owwydn...LA1_0.pdf?dl=0

                    Two questions that I'm trying to answer now:
                    1. On page 7 it states that the voltage should be between 58Vdc and 66Vdc - is this an issue if mine is only getting 33Vdc? Or is 33V some sort of standby voltage.
                    2. On page 10 it shows the pin layouts. For all the negative pins, is it possible to check if there is a return path in the circuit (where would I probe to check the negative side isn't open)?


                    Thanks for your help

                    Edit: here is the video showing the behavior of the buttons:https://youtu.be/3LndYVC7nLE
                    Last edited by drjaydenm; 09-01-2018, 02:03 AM.

                    Comment


                      #11
                      Re: Dell U2713Hb No Display

                      As indicate in my post #5, it has 33V feeding the Voltage booster converter circuit but since you do have any command signal to turn on the backlights circuit so the output Voltage to the LEDs stays at 33V instead of boosted up to more than 50V to drive the LED's.
                      Last edited by budm; 09-01-2018, 02:18 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


                        #12
                        Re: Dell U2713Hb No Display

                        Here's a schematic for the LED power supply area involving the 4 wires - pins 10-13 (blue, orange, purple, white) coming from the main board.

                        It looks like pins 10 and 12 aren't connected to anything (missing resistors or caps that were never soldered on).

                        Do the labels of on/off and brightness for those lines look correct here? If that is correct, then I will start tracing pin 13 through the main board.
                        Attached Files

                        Comment


                          #13
                          Re: Dell U2713Hb No Display

                          Are you getting about 380 ~ 400VDC measured right between the two legs of the main filter cap (120uF 450VDC)?
                          The power supply board has PFC Voltage booster circuit (the diode and the MOSFET and the yellow inductor to the right of the bridge rectifier), the PFC will run when the power supply board receives the PS-ON control signal form the logic board.
                          I would not try to trace the backlights circuit at this point, I would concentrate on those 4 pins that show 0V back to the logic board to see where they go.

                          OZ9908: pin 28 is ENA pin (Enable), pin 23 is the Gate drive for the Boost converter circuit.
                          Attached Files
                          Last edited by budm; 09-03-2018, 09:44 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


                            #14
                            Re: Dell U2713Hb No Display

                            Thanks, I'll start working on the logic board and see if anything is going wrong there.

                            I measured the filter cap and it was at 400VDC when the power was first turned on, then went down to 320VDC over about 10 seconds and sat there.

                            Comment


                              #15
                              Re: Dell U2713Hb No Display

                              So it looks like the PFC Booster did come on and then turn off.
                              @230VAC input, the DCV on the cap will be about 230VAC x 1.414 = 325VDC of the filter cap.
                              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


                                #16
                                Re: Dell U2713Hb No Display

                                I have traced back both the power button and PS_ON connector to the CPU on the logic board. There is 0V on the PS_ON (CN1/12) wire both before and after the power button is pressed. There aren't any opens along this path. Everything seems OK here.

                                On the power button side (J12/1, J12/2), J12/2 sits at 2.56V and gets grounded to 0V when pressed. However TP_Unamed (next to R176) shows 0.82V potential when the button is pressed.
                                Is this going to cause issues with the CPU identifying the button is pulled to ground?
                                Attached Files

                                Comment


                                  #17
                                  Re: Dell U2713Hb No Display

                                  Forgot to mention that I pulled the heatsink off the CPU to check the model. Turned out to be model STDP9320-BB. I can only find a databrief sheet though, so not much help.

                                  It is strange, it looks like the CPU gets the input for power on, but does not output the PS_ON signal. Is there a way to check if the CPU is working at all?
                                  Attached Files

                                  Comment


                                    #18
                                    Re: Dell U2713Hb No Display

                                    I may have narrowed down the problem - still not sure if it is the problem, or just a side-effect though.

                                    On the logic board, the LVDS power circuit is off in standby mode. Brining the MOSFET gate down (highlighted in image) to ground for a second starts it up, but then something shorts which brings the whole circuit down to 7V from 12V and chews 1.5A. The voltage regulator ground gets very hot after a while. Could the voltage regulator be bad? Or is the heat due to the short elsewhere? I can't find anywhere else on the board that gets hot.
                                    Attached Files

                                    Comment


                                      #19
                                      Re: Dell U2713Hb No Display

                                      Originally posted by drjaydenm View Post
                                      I may have narrowed down the problem - still not sure if it is the problem, or just a side-effect though.

                                      On the logic board, the LVDS power circuit is off in standby mode. Brining the MOSFET gate down (highlighted in image) to ground for a second starts it up, but then something shorts which brings the whole circuit down to 7V from 12V and chews 1.5A. The voltage regulator ground gets very hot after a while. Could the voltage regulator be bad? Or is the heat due to the short elsewhere? I can't find anywhere else on the board that gets hot.
                                      So does the Voltage regulator get hot if you did not force on that switched MOSFET which supplies the switched 12V to run the T-CON board?
                                      Do you still get switched 12V if the T-con board is not connected?
                                      What output Voltage do you have on that regulator when it gets hot?
                                      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


                                        #20
                                        Re: Dell U2713Hb No Display

                                        That was all tested with the timing controller board disconnected - the scaler board is connected straight to the bench supply, bypassing the SMPS too. The regulator usually outputs 12V, even if the input is a bit higher at 12.6V (that's what the monitor SMPS was outputting). It consumes 0.233A in standby which I am guessing is mainly the CPU. During this period, I've had it running for hours with no heat apart from the usual CPU heatsink.

                                        Once the MOSFET is manually switched on by temporarily brining the gate voltage down, it stays on. The power supply reports that the input voltage drops to 7V and is outputting 1.5A (fluctuating a little). The regulators ground pin heats up over the period of say 15 seconds and I turn it off so that it doesn't blow up Measuring the voltage over the two pins of the voltage regulator shows 7V as well.

                                        It felt to me like a short in the TCON circuit, but the resistances there all seem to be outside the range of providing 1.5A of current
                                        Last edited by drjaydenm; 10-02-2018, 03:14 PM.

                                        Comment

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