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    attempt to repair power supply board

    This is a continuance from my last post---> https://www.badcaps.net/forum/showthread.php?t=66677

    Hp f2105 monitor with a dead power supply board. id like to repair it myself instead of replacing with a different one. I like the challenge of learning something new that interests me.

    i decided to do some voltage reading comparison between a good working monitor, that was given to me and the one that i have that doesnt work. I have found an issue with mine but im not sure what to make of it. Checking the voltage at F851 and F852 the voltage fluctuates between 10vdc and 14vdc. the voltage at the same locations (F851 & F852) , on the good monitor, is a steady 18.98vdc any help is greatly appreciated.

    #2
    Re: attempt to repair power supply board

    First of all get the schematic. It will be much much easier when you have a diagram of faulty device.
    What is the board number of power supply? I couldn't find on the pictures.
    Laptops and computers repair.

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      #3
      Re: attempt to repair power supply board

      board number is 4H.L1S02.A21 im searching for a schematic as we speak, so far no luck yet.

      here as some pics of the board
      Attached Files
      Last edited by ryn0909; 01-25-2018, 09:46 PM. Reason: update

      Comment


        #4
        Re: attempt to repair power supply board

        If you can't find a schematic, provide very good high res. straight on pictures of both sides of the board, that way we can follow the traces and "maybe" help with the repair.
        We can't trace the circuit with only top views.
        Have you changed the small elecrolytics like c606 c611?
        Last edited by R_J; 01-26-2018, 11:39 AM.

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          #5
          Re: attempt to repair power supply board

          ok im working on the images as we speak ill post asap


          im still trying to get a schematic for it but hp isnt wanting to cough it up
          Last edited by ryn0909; 01-26-2018, 09:06 PM.

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            #6
            Re: attempt to repair power supply board

            here are some pics let me know if u need more
            Attached Files

            Comment


              #7
              Re: attempt to repair power supply board

              Are you measuring that voltages with all other boards connected?
              What if inverter and audio boards disconnected?

              Comment


                #8
                Re: attempt to repair power supply board

                good question.... i dont exactly remember. ill take the measurement again and report back. ill do that rite now

                Comment


                  #9
                  Re: attempt to repair power supply board

                  Originally posted by Dumah Brazorf View Post
                  Are you measuring that voltages with all other boards connected?
                  What if inverter and audio boards disconnected?
                  ok well after hooking it back up with all boards connected, i checked the voltage and it was fluctuating between 10vdc and 14vdc. i unplugged each board 1 by 1 and when i unplugged the logic interface board, the voltage stabilized at 18.98vdc. there was no change with any of the other boards plugged or unplugged
                  Last edited by ryn0909; 01-27-2018, 05:33 AM.

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                    #10
                    Re: attempt to repair power supply board

                    Well, let's have a look at the logic board.

                    Comment


                      #11
                      Re: attempt to repair power supply board

                      Originally posted by Dumah Brazorf View Post
                      Well, let's have a look at the logic board.
                      i know for certain that the issue is in the power supply board because when i attach the board from my other monitor (same model) everything works fine. i just now took measurements at the connector on the power supply board (cn702) that connects to the logic board see attached pic
                      Attached Files

                      Comment


                        #12
                        Re: attempt to repair power supply board

                        I think you caused some damage working on it.
                        I see several scratches on the pcb and a trace probably ripped near a cap.
                        Clean the board from all that dust/fur/hairs and check for continuity between solder points at the ends of all the traces that present scratches or you worked on.
                        Attached Files
                        Last edited by Dumah Brazorf; 01-27-2018, 07:06 AM.

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                          #13
                          Re: attempt to repair power supply board

                          Here the pads are gone. Make sure there's continuity between the soldering points of ic403 and the first component connected to that traces.
                          So again check all of your soldering for continuity.
                          I also see some solder between that diode and that resistor, check if it's ok on the other board.
                          Attached Files
                          Last edited by Dumah Brazorf; 01-27-2018, 07:16 AM.

                          Comment


                            #14
                            Re: attempt to repair power supply board

                            What's that? Is there at least some solder on the central leg?
                            You're using too much heat and probably no flux, your solder pads/points are mostly destroyed.

                            If the solder point is destroyed jump wire to the nearest solder point.
                            Attached Files
                            Last edited by Dumah Brazorf; 01-27-2018, 07:32 AM.

                            Comment


                              #15
                              Re: attempt to repair power supply board

                              yes there is continuity at the points of concern i made double sure of that. also the problem exsisted before i replaced the caps

                              Comment


                                #16
                                Re: attempt to repair power supply board

                                Either you are using to much or you are staining to long on those small pads

                                If you put heat on a pad and the solder does not flow to Desoldiering wick then get off of it and put new solder on the joint and try it again if that does not work use some soldering flux and try again or increase your heat a little bit


                                I hope this helps


                                I use a Desoldiering Gun which makes easier but you can have the same problem if you use to much heat or you stay on it to long or you put to much pressure on the tip can do the same thing

                                When I use the Desoldiering Gun I have the temperature set for 775* F but with this setting I am on the the soldering joint and off of it very quickly

                                Now for multilayer boards it gets a little trickier this is when I have to set it to 890* F
                                and I might have to leave on the there a little bit more for ground plains to begin to flow with small soldering joints I leave it there until it flows and get off it

                                I have also ran across some boards are just plain s**t and those I have setting at 650* F and sometimes you have have to leave there for a little bit more for the solder to flow I do not like working with these boards you can tell if it’s this type of board because if you have it set for 775*F and turns the area around the pad black or brown it’s probably one of those type board
                                Last edited by sam_sam_sam; 01-27-2018, 08:12 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

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                                  #17
                                  Re: attempt to repair power supply board

                                  thank you but the solder joints are fine, they dont look the best but they arent shorted and they do have continuity.

                                  Comment


                                    #18
                                    Re: attempt to repair power supply board

                                    Could you measure the voltages at the connector on the good board?
                                    And on the bad with the logic one disconnected.
                                    Is C811 missing?
                                    Last edited by Dumah Brazorf; 01-27-2018, 11:50 AM.

                                    Comment


                                      #19
                                      Re: attempt to repair power supply board

                                      I'll ask again, did you replace the small elec. caps in the primary?

                                      Comment


                                        #20
                                        Re: attempt to repair power supply board

                                        Originally posted by R_J View Post
                                        I'll ask again, did you replace the small elec. caps in the primary?
                                        sorry about that, i totally missed that question. No i have not changed the small electrolytic caps on the primary

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