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P2317H not turning on

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    P2317H not turning on

    Hi Everyone,

    I have a problem with my dell P2317Hb
    No reaction to power button press.
    Boardnumber:
    L3101-1M
    48.7AA02.01M
    No schematic or boardview found yet.

    Power supply board itself looks good, 5v Is present on the wires that goes to secondary Logic Board. As soon as i connect the to boards then this drops to 1.4v.
    1.4v also present on the power button sideboard, and when I press the button, voltage drops to 0 then comes back but nothing happpens. Checked all wires no broken found.
    Can anyone help me trace what could be the problem?


    Thanks.
    Attached Files

    #2
    Re: P2317H not turning on

    Its only 1.12 volts now

    Comment


      #3
      Re: P2317H not turning on

      Find a "1MHz 1A Synchronous Step-Down Regulator"


      According to Datasheet the equasion is good and the output should be 1.2v indeed,
      Because Vout=0.6V*(1+(163K/163K))=0,6v*(1+1)=1.2V So this seems fine.
      So my thinking is like this: If the powerbutton pressing drops voltages to 0 for a second then something else must be not switch on.
      Attached Files
      Last edited by questore; 05-27-2022, 12:33 PM.

      Comment


        #4
        Re: P2317H not turning on

        Originally posted by questore View Post
        Find a "1MHz 1A Synchronous Step-Down Regulator"


        According to Datasheet the equasion is good and the output should be 1.2v indeed,
        Because Vout=0.6V*(1+(163K/163K))=0,6v*(1+1)=1.2V So this seems fine.
        So my thinking is like this: If the powerbutton pressing drops voltages to 0 for a second then something else must be not switch on.
        1. Strange thing is that acoring to datasheet the VIN should be voltage higher than 4 Volts, and its is 1.2V also, so how is the regulator even working?
        Is it possible that it is not and the 1,2volt is coming from somewhere else and it only would go up if button is pressed and something gives more power to VIN?
        Also VIN and LX is not sorted.
        Readings to ground are:
        - Pin 1: 1.5K
        - Pin 2: GND
        - Pin 3: 1.5K
        - Pin 4: 1.5K
        - Pin 5: 8,2K
        Last edited by questore; 05-28-2022, 02:58 AM.

        Comment


          #5
          Re: P2317H not turning on

          After letting is rest 24 hours unplugged. The following changed:
          The LX has only 0.28v
          Also cheched power button line and seems to have no broken resistor and when button pressed, the voltage drop reaches the main IC.
          Any idea why 5v not raising after button press?

          Comment


            #6
            Re: P2317H not turning on

            Your problem is likely with the power supply not the main board, the power supply can't supply any current on the 5v standby line.
            I would suspect the small electrolytic (PT504?) in the primary for the vcc line of the controller ic.
            Last edited by R_J; 05-29-2022, 02:46 PM.

            Comment


              #7
              Re: P2317H not turning on

              I think I can borrow another same type power supply to test that theory.
              Thanks, I will get back to you with the result.

              Comment


                #8
                Re: P2317H not turning on

                In the meantime i have checked.power board and the 5.12v is present in the other side of the 360kohm resistor, so I wonder...isn't it means that the power board is ok?
                Attached Files
                Last edited by questore; 05-30-2022, 06:41 AM.

                Comment


                  #9
                  Re: P2317H not turning on

                  I had time while waiting for the power supply.
                  So i have checked every component on the logic board and found a bad diode that reads 0.5v and 0.3v in both ways on diode mode.
                  I assume its fault can be the cause of the low power since its directly connected on the input rail of the board.
                  According to the internet it is a "UDZ5V6B" SOD-323 diode.
                  Attached an image (its the one with the mark of BC), please correct me if I'm wrong.
                  Attached Files

                  Comment


                    #10
                    Re: P2317H not turning on

                    I cannot find component, since these are only comes with a package of 3000pcs and this is more costly then buying a new board.

                    Any replacement suggestions?

                    Comment


                      #11
                      Re: P2317H not turning on

                      That diode is a 5.6 volt 200mw zener diode, they can be found everywhere, Check the voltage across it. If it is across the 5 volt input, it is good, and this is not your problem.
                      Last edited by R_J; 05-31-2022, 02:40 PM.

                      Comment


                        #12
                        Re: P2317H not turning on

                        Originally posted by questore View Post
                        I cannot find component, since these are only comes with a package of 3000pcs and this is more costly then buying a new board.

                        Any replacement suggestions?
                        Here try this place for them this is the actual part number “ UDZ5V6B-7 ”

                        https://www.questcomp.com/part/4/udz...ign=partsearch

                        Here is the data sheet

                        https://cdn.badcaps-static.com/pdfs/...5bde1316c9.pdf

                        I have personally ordered from them in the past several times when I am finding hard to find parts yes they do have a minimum amount for an order
                        Last edited by sam_sam_sam; 06-01-2022, 10:50 AM.
                        9 PC LCD Monitor
                        6 LCD Flat Screen TV
                        30 Desk Top Switching Power Supply
                        10 Battery Charger Switching Power Supply for Power Tool
                        6 18v Lithium Battery Power Boards for Tool Battery Packs
                        1 XBox 360 Switching Power Supply and M Board
                        25 Servo Drives 220/460 3 Phase
                        6 De-soldering Station Switching Power Supply 1 Power Supply
                        1 Dell Mother Board
                        15 Computer Power Supply
                        1 HP Printer Supply & Control Board * lighting finished it *


                        These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

                        1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
                        2 Hem Saw Computer Stack Board

                        All of these had CAPs POOF
                        All of the mosfet that are taken out by bad caps

                        Comment


                          #13
                          Re: P2317H not turning on

                          Originally posted by R_J View Post
                          That diode is a 5.6 volt 200mw zener diode, they can be found everywhere, Check the voltage across it. If it is across the 5 volt input, it is good, and this is not your problem.
                          This is not my problem? I don't understand! Are you meaning changing the bad diode won't fix my standby 5V being 1.2V?

                          Comment


                            #14
                            Re: P2317H not turning on

                            Originally posted by questore View Post
                            This is not my problem? I don't understand! Are you meaning changing the bad diode won't fix my standby 5V being 1.2V?
                            Sorry I misunderstood, I thought the 5 volts was present and only dropped when the power button was pressed. Replacing the diode should resolve the problem.
                            If the diode is across the 5 volt input to the main board the diode is likely only for protection If the main board is removed and the 5 volts is not high, you can remove it to test the operation of the monitor, after testing install a new 5.6v zener diode.

                            Comment


                              #15
                              Re: P2317H not turning on

                              Originally posted by R_J View Post
                              Sorry I misunderstood, I thought the 5 volts was present and only dropped when the power button was pressed. Replacing the diode should resolve the problem.
                              If the diode is across the 5 volt input to the main board the diode is likely only for protection If the main board is removed and the 5 volts is not high, you can remove it to test the operation of the monitor, after testing install a new 5.6v zener diode.
                              Removed the bad diode, no change
                              Any idea?

                              Comment


                                #16
                                Re: P2317H not turning on

                                So it is not the diode causing the voltage to drop, It is one of two things, either the power supply can not supply enough current for the main board or something else on the main board is loading down the 5v. The easiest way would be to try that other power supply board.

                                Comment


                                  #17
                                  Re: P2317H not turning on

                                  Or i can hook up a lab power supply to see if it is drawing power of 5v fine.

                                  Comment


                                    #18
                                    Re: P2317H not turning on

                                    Originally posted by questore View Post
                                    Or i can hook up a lab power supply to see if it is drawing power of 5v fine.
                                    Yes, you can do that or you could load the 5v line on the power supply with something like a 10Ω for about 500ma draw or a 4.7Ω 5watt to draw 1 amp.

                                    Comment


                                      #19
                                      Re: P2317H not turning on

                                      Originally posted by R_J View Post
                                      Yes, you can do that or you could load the 5v line on the power supply with something like a 10Ω for about 500ma draw or a 4.7Ω 5watt to draw 1 amp.
                                      Disconnected the two board and hooked a lab power supply on the.5v. input.
                                      Pushed 5.1v and it started drawing 0.020A and the power led started flashing. Maybe its flashing because the rest of the connection pins missing but since 0.020 is small amount, i would suspect the problem is the power supply board. Feel free for dicussion..

                                      Comment


                                        #20
                                        Re: P2317H not turning on

                                        It could be flashing for many reasons, no input signal, no backlights etc.
                                        >Goto #6

                                        Comment

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