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HP w1858 - No Power

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    HP w1858 - No Power

    I have a HP w1858 monitor that I got used when I was back in the states. It had some occasional power issues where the screen would become totally unresponsive after going into power-saving mode. It would have to disconnected from the PC and reconnected to respond again. While unresponsive the monitor would not turn on at all, no lights, nothing. I didn't have time to mess with it at the time, so it was set aside.

    I recently came upon a little free time and thought I would check the monitor out again. This time, however, it is totally unresponsive from the start. I tried multiple cables, multiple computers and I still get nothing.

    I came across this forum and was hoping the problem would be something simple, but from my limited knowledge, it seems it may be a mess. The caps show no obvious signs of bulging or leaking, the seem to be sitting fairly flush. I did notice some black soot(?) near the main capacitor and transformer on the power board. Encompassed in the soot mess are: positive lead on the main capacitor had some black attached to it, the two blue inrush current limiters(?) appear a little black, the tan resistor was also pretty black (but tested ok), and the side of the transformer also seemed to have some black on the side. A lot of this looked like collateral mess, and I don't see who the main culprit is. Additionally, on the back side of the board there is a section that looks like it might have gotten a bit toasted, along with several hard brown drips on the back, of which I have no clue where they came from.

    So all in all, a mess, but I was hoping an educational one. If by some miracle this can possibly be fixed by replacing a few parts, awesome. If not, hopefully it could serve as an excellent example of a board to trash.

    If any additional photos could be useful let me know.

    Thanks for your advice and time in advance.
    Attached Files

    #2
    Re: HP w1858 - No Power

    the big yellow transformer needs resoldering for a start.

    Comment


      #3
      Re: HP w1858 - No Power

      Aside from the black soot on the corner, was there something specifically that you saw on the transformer showing it needed to be resoldered? The black seemed to be external to the protective tape and could be rubbed off. This is a learning experience for me, so I'm curious why you specifically pointed out the transformer.

      Without obviously distorted caps or other clearly damaged parts I am at a loss. I'm wondering what the general train of thought is or if there is a mental checklist to go through to check specific components in a case like this. Thanks!

      Comment


        #4
        Re: HP w1858 - No Power

        nothing to do with soot, i was looking at the solder-side foto.

        Comment


          #5
          Re: HP w1858 - No Power

          So what DCV do you on the two legs of the main filter cap int the primary side? Be careful since you are making measurement in the primary side of the circuit, do not touch anything with your hands or body.
          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: HP w1858 - No Power

            The main filter cap showed about 137V plugged in.

            Comment


              #7
              Re: HP w1858 - No Power

              Just the power supply by itself, try heating up the startup cap C903 right next to the main filter cap with hair dryer to see if you will then get some Voltages at the white connector.
              You also check the DCV right at the two legs of the startup cap to see what you have.
              BTW, you already check the rectifier diode in the secondary side to make sure they are not bad?
              Check the Source resistor R914 also.
              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: HP w1858 - No Power

                Ran some of the tests you suggested. The startup cap is running at about 14V cold. I didn't notice any difference after heating it up. The resistor tested at 1.4 ohms. Interestingly enough, the D900 diode seems to be shot. Not sure if that's the only problem, but I'm pretty sure I should be getting something through it. Thanks for the help so far. I really appreciate it!

                Comment


                  #9
                  Re: HP w1858 - No Power

                  Originally posted by Corbid View Post
                  Ran some of the tests you suggested. The startup cap is running at about 14V cold. I didn't notice any difference after heating it up. The resistor tested at 1.4 ohms. Interestingly enough, the D900 diode seems to be shot. Not sure if that's the only problem, but I'm pretty sure I should be getting something through it. Thanks for the help so far. I really appreciate it!
                  How is the D900? Shorted between Anode and Cathode? You should post the pictures and also test it again off the board.
                  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: HP w1858 - No Power

                    The D900 appears to be open. I get no readings from it running in either direction. Work is busy but I'll try to pull the diode out soon and get some more pictures uploaded. Thanks again, more to come.

                    Comment


                      #11
                      Re: HP w1858 - No Power

                      Hello again. Sorry for the delay. I take back my last comments on the diode as well. Checked it again and it seems alright. Any other suggestions of what to check? Thanks!

                      Comment

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