Hp 1955

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  • terminatorX
    Senior Member
    • Feb 2012
    • 63

    #1

    Hp 1955

    The hp 1955 (Benq 48.L1A02.A00) the monitor was just totaly dead.
    So I opened it and removed the power board. So I found out that one of the three pins on the power cable connector was blown. If you look at the "green" side its the left pin. the center pin was loose and the right pin had cracked solder. So I resoledered it. I think I did I decent job on that but it didn't help at all. The power led didn't go on. also here is no bulging on capacitators or something similar. What do you think, could it be both the C5707 transistors and the picofuse maybe?


  • PlainBill
    Badcaps Legend
    • Feb 2009
    • 7034
    • USA

    #2
    Re: Hp 1955

    Don't post pictures inline. It seriousl inconveniences retiredcaps and pisses me off.

    No, it's not the picofuse, and it's not the c5707s.

    Let's do this logically. What is the voltage across the large cap? On the top view there is an 8 pin IC partially obscured the green wire. What is the part number of that IC?

    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

    • terminatorX
      Senior Member
      • Feb 2012
      • 63

      #3
      Re: Hp 1955

      Thanks for respons. Just want to emphasize that I'm a real newbie.
      Can I check the large cap without current running through? Not really in the mood of killing my self if do something wrong...
      Ic part number should be 1200AP40,CPBC, 0449 close to a spot called IC601.

      Comment

      • retiredcaps
        Badcaps Legend
        • Apr 2010
        • 9271

        #4
        Re: Hp 1955

        Originally posted by terminatorX
        Can I check the large cap without current running through?
        No.

        Not really in the mood of killing my self if do something wrong...
        1) Assuming your mains AC is 110 to 120V AC and you have a manual range multimeter, set it to 200V DC. Yes, set it to DC.

        2) Plug your black probe into the COM jack. Plug your red probe into the Volts jack.

        3) Put your red probe on the positive leg of the capacitor. Put your black probe on the negative leg of the capacitor.

        4) If it is working properly, we expect a stable DC voltage reading somewhere in the 165V to 170V DC range.

        120 mains AC x 1.414 (rectified) = 169.68V DC
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        Comment

        • terminatorX
          Senior Member
          • Feb 2012
          • 63

          #5
          Re: Hp 1955

          Nope the AC is 230V. Don't know how to determine which leg is positive or negative (or even if that matters). Just to make clear....should I plug in the board to the wall as is or mount it back to the screen first?

          Comment

          • selldoor
            Slow Learner
            • Dec 2010
            • 7870

            #6
            Re: Hp 1955

            Please can you update your profile with at least the country you are in.

            The previous instructions need amending accordingly
            TAKE EVEN GREATER CARE

            1) Assuming your mains AC is 230AC and you have a manual range multimeter, set it to 600V DC. Yes, set it to DC.

            2) Plug your black probe into the COM jack. Plug your red probe into the Volts jack.

            3) Put your red probe on the positive leg **of the capacitor. Put your black probe on the negative leg of the capacitor. YES IT DOES MATTER

            4) If you rectify 230 volts AC RMS with bridge rectifier, without Filter capacitor, the meter will read 230 X 1.414 Volts = 325.22 Volts exactly.

            So If it is working properly, we expect a stable DC voltage reading somewhere in the 320V to 350V DC range.

            ** The capacitor probably has a white or pale blue stripe down one side
            with - - - - - - minus signs in it the leg on the same side as the stripe
            is the negative. Note both legs are high voltage.

            The monitor does not have to be rebuilt and I believe for this test the power board can stand alone. Do not rest it on anything metallic and do not touch it other than with the probes. Do not let them slip off the legs and do not touch the board after the test until it has been switched off for at least 5 minutes.

            If you have any time for reading read this:https://www.badcaps.net/forum/showthread.php?t=10419 there are revisions within it so start at
            post 18 .It will give you advanced insight into what further tests may be required.
            Last edited by selldoor; 02-13-2012, 02:54 PM.
            Please upload pictures using attachment function when ask for help on the repair
            http://www.badcaps.net/forum/showthread.php?t=39740

            Comment

            • terminatorX
              Senior Member
              • Feb 2012
              • 63

              #7
              Re: Hp 1955

              Thanks for your good help!

              If you rectify 230 volts AC RMS with bridge rectifier, without Filter capacitor, the meter will read 230 X 1.414 Volts = 325.22 Volts exactly.
              Not really sure what this is about...AC RMS....

              To be exactly sure what I'm doing. I don't really se an adequat marking for +/- so would it be a good guess to say at the side where there are those minus marking should be the minus pin?
              Attached Files

              Comment

              • selldoor
                Slow Learner
                • Dec 2010
                • 7870

                #8
                Re: Hp 1955

                Yes - I believe that is what I said?
                [Quote]
                ** The capacitor probably has a white or pale blue stripe down one side
                with - - - - - - minus signs in it the leg on the same side as the stripe
                is the negative.[Quote]
                Please upload pictures using attachment function when ask for help on the repair
                http://www.badcaps.net/forum/showthread.php?t=39740

                Comment

                • terminatorX
                  Senior Member
                  • Feb 2012
                  • 63

                  #9
                  Re: Hp 1955

                  Hahha sorry read that part quickly, thought you meant the actual pin was suppose to have a marking....

                  But you still didn't describe what AC RMS rectifier ...filter capacitator...is.
                  Kind of why I quoted it and wrote
                  Not really sure what this is about...AC RMS....

                  Comment

                  • terminatorX
                    Senior Member
                    • Feb 2012
                    • 63

                    #10
                    Re: Hp 1955

                    Never mind I did the testing. I have a semi automatic DMM. The capacitator showed 0.5V to verify the plausability of the test I also tested my hp 1940 powerboard that I also have a problem with that is in another thread it showed a very stable 325V.
                    Knowing this what do you belive is the reason the power connector blew it's two soldering points? Is it really the capacitor that is boken maybe the current is inhibited somewhere else...

                    Comment

                    • PlainBill
                      Badcaps Legend
                      • Feb 2009
                      • 7034
                      • USA

                      #11
                      Re: Hp 1955

                      1. Benq is notorious for shoddy soldering

                      2. The pins of the power connector can receive a lot of stress when the power cord is plugged in..

                      3. The fuse in the power supply would blow long before any excessive load would destroy the solder on the pins of the power connector.

                      Resolder the pins!!!

                      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

                      • terminatorX
                        Senior Member
                        • Feb 2012
                        • 63

                        #12
                        Re: Hp 1955

                        Ok...
                        So would you say the capacitator is bad? Do you want me to resolder the power connector pins? I just did that.....

                        Comment

                        • PlainBill
                          Badcaps Legend
                          • Feb 2009
                          • 7034
                          • USA

                          #13
                          Re: Hp 1955

                          Originally posted by terminatorX
                          Ok...
                          So would you say the capacitator is bad? Do you want me to resolder the power connector pins? I just did that.....
                          Let's walk through this. I'm seeing references to another monitor, don't do that. It's hard enough as it is.

                          1. What is the voltage across the large cap?

                          2. Using the minus (-) lead of the large cap as ground, what are the voltages on the pins of the NCP1200AP40? Do this carefully.

                          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

                          • Krankshaft
                            Badcaps Legend
                            • Jan 2007
                            • 2328
                            • USA

                            #14
                            Re: Hp 1955

                            For easier troubleshooting I've attached the main switcher IC datasheet.

                            Post the readings Plainbill suggested and we'll get a better handle on the status of the IC.
                            Attached Files
                            Last edited by Krankshaft; 02-17-2012, 08:30 PM.
                            Elements of the past and the future combining to make something not quite as good as either.

                            Comment

                            • selldoor
                              Slow Learner
                              • Dec 2010
                              • 7870

                              #15
                              Re: Hp 1955

                              Originally posted by terminatorX
                              Ok...
                              So would you say the capacitator is bad? Do you want me to resolder the power connector pins? I just did that.....
                              No Not the power connector pins - the pins of all the components ringed in red on the earlier picture.

                              I understand you to say that the voltage across the Big cap is 0.5v.

                              Whilst it could be the cap, this may be due a fault in the bridge rectifier
                              which I will mark in a picture. This should be tested initially with the power OFF, with your meter on a test diode setting.
                              Take a multi-Meter and switch it to Ohm x 1
                              Test between one of the "~" and "+" legs.
                              You should get either an almost-zero reading in one direction, and when you reverse the test probes, you should get an almost infinite reading.
                              Now try the same between this "~" leg and "-".
                              Same as above.
                              Now repeat the same tests with the other "~" leg, and "+", and then "-".
                              Same as above.
                              If you either get almost zero or almost infinite in BOTH directions, then the rectifier burnt out.

                              If the rectifier has gone the fuse will probably also be blown - can you test it. (POWER OFF) Can you post any numbers on the Rectifier and the fuse.
                              Attached Files
                              Please upload pictures using attachment function when ask for help on the repair
                              http://www.badcaps.net/forum/showthread.php?t=39740

                              Comment

                              • terminatorX
                                Senior Member
                                • Feb 2012
                                • 63

                                #16
                                Re: Hp 1955

                                So PlainBills and Krankshafts part.
                                Weird part is that i retested the large cap voltage and it fluctuated around 1.4XX volts instead what I said before around 0.5V.

                                Hope I done this properly.
                                Pin 8 had about the same voltage as the large cap voltage and pretty much the same fluctuation. They were more or less synchronized.
                                Pin 7 read -0.008 but also fluctuating. Pin 6 about 0.203. Pin 5-1 read stable zero (pin 3 read actually 0.001) To mention when started reading it read a value that increased when retested it started about the same initial value increasing the same way. All fluctuating values were like this.


                                Selldors part:

                                I followed:
                                http://www.youtube.com/watch?v=dqkT6hF0O3E

                                and pretty much got the same reading maybe just below what was on the vid.
                                For some reason it doesn't seem to work ohm way. If I have low ohm reading it all read "OL"when I set it to M(ega I suppose) ohms then it starts to read and one direction is always reading a bit higher.

                                So I don't know why it's not matching with diode testing...

                                when You say fuse do you mean the picofuse?

                                Just to mention nothing has been soldered out of the board yet.

                                Comment

                                • selldoor
                                  Slow Learner
                                  • Dec 2010
                                  • 7870

                                  #17
                                  Re: Hp 1955


                                  I followed:
                                  http://www.youtube.com/watch?v=dqkT6hF0O3E

                                  and pretty much got the same reading maybe just below what was on the vid.
                                  For some reason it doesn't seem to work ohm way. If I have low ohm reading it all read "OL"when I set it to M(ega I suppose) ohms then it starts to read and one direction is always reading a bit higher.

                                  So I don't know why it's not matching with diode testing...

                                  .
                                  My turn to not understand- Can you post the actual readings with what leads on what pins.

                                  when You say fuse do you mean the picofuse?
                                  No ,I mean the mains fuse - I have marked what I think is a fuse It will probably say on the board and on the fuse but cant see. (This is why good clear photos are important)

                                  Have you resoldered the joints yet?
                                  Attached Files
                                  Please upload pictures using attachment function when ask for help on the repair
                                  http://www.badcaps.net/forum/showthread.php?t=39740

                                  Comment

                                  • terminatorX
                                    Senior Member
                                    • Feb 2012
                                    • 63

                                    #18
                                    Re: Hp 1955

                                    Have not resoldered yet will maybe do that at weekend.

                                    Ok so i hope this is right. When I talk about the rectifier I mean; (+,1,2,-) pins.

                                    Using the DMM in diode mode i get:
                                    Red on leg + and black on leg1= OL
                                    Red on leg 2 and black on leg - =OL
                                    Black on leg + and red on leg 1= 0.495
                                    Black on leg 2 and red on leg - =0.506
                                    Red on leg 1 and black on leg 2 =OL
                                    Black on leg 1 and red on leg 2= OL

                                    But when using in ohm mode it's just really weird. To mention it does work properly since I tested it on a couple of resistors on the board and right values where displayed.

                                    Here are a couple of values it's more values at one reading because my DMM show different values when setting range...

                                    Red on leg + and black to both leg 1 and 2 =2MΩ
                                    Black on leg + and red on leg 1= 34.67kΩ, 145.1kΩ, 0.642MΩ and 2.07MΩ
                                    Black on leg + and red on leg 2= 39.7kΩ, 165.9kΩ, 0.72MΩ and 2.28MΩ
                                    Red on leg - and black on leg 2= 40.21kΩ, 166.5kΩ, 0.738MΩ and 2.42MΩ
                                    Red on leg - and black on leg 1= 40.49kΩ, 167.5kΩ, 0.739MΩ and 2.39MΩ

                                    By the way, how should I test the fuse before resoldering?

                                    Comment

                                    • jayoung
                                      Senior Member
                                      • May 2011
                                      • 172

                                      #19
                                      Re: Hp 1955

                                      Set the DMM on 200 ohm scale and put one probe on each leg of the fuse. You should get a reading less than 1 ohm (same as touching the two probes together).

                                      Comment

                                      • selldoor
                                        Slow Learner
                                        • Dec 2010
                                        • 7870

                                        #20
                                        Re: Hp 1955

                                        Hmm! test fuse?? Whilst looking for an easy way to show this I noticed that this board has a switch. When you were testing the BIG Cap
                                        was it definitely switched on?
                                        If it was can you test the switch. - same as the fuse but obviously resistance when on and none when off.
                                        Please upload pictures using attachment function when ask for help on the repair
                                        http://www.badcaps.net/forum/showthread.php?t=39740

                                        Comment

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