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HP 1955 Monitor Repair Guide

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    #41
    Re: HP 1955 Monitor Repair Guide

    Hi all,
    I would just like to double check with someone on this forum regarding the signaling transistors (3904 and 3906) exactly which ones are the npn and pnp...I'm getting confused trying to measure in circuit as I have so many things blown. I've uploaded a copy of Krankshaft's picture (I hope that's okay) as a reference to the devices. I think the Q811 is the npn and the Q810 is the pnp (as pictured), but I can't figure out Q802 and Q803 (upper left side of the picture) as they are both damaged on my board....Can anyone help?
    Thanks in advance
    Attached Files
    Last edited by garrysoh; 10-16-2010, 12:16 PM. Reason: typo

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      #42
      Re: HP 1955 Monitor Repair Guide

      Originally posted by garrysoh View Post
      Hi all,
      I would just like to double check with someone on this forum regarding the signaling transistors (3904 and 3906) exactly which ones are the npn and pnp.
      2N3904 is NPN and 2N3906 is PNP.
      Friends don't let friends buy Samsung ....

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        #43
        Re: HP 1955 Monitor Repair Guide

        I'm sorry, but I guess my question wasn't clear. I know that the 3904 is the npn and the 3906 is the pnp, but I was looking for confirmation in circuit. I know that there is a pair (npn and pnp) is used for each FET. I also know the location on the board of each pair thanks to the picture that circles each pair. What I am not 100% sure on is which one, as shown in the picture, is the 3904 npn and which one is the 3906 pnp...
        Thanks in advance.

        Comment


          #44
          Re: HP 1955 Monitor Repair Guide

          I have one of these monitors and I am finding there is a buzzing coming from the inverter board. Near the entry of the 110v power supply. It could be coming from the transformer for the mains power, or the caps that are near the entry of the 110v. Does anyone have a part number for a replacement transformer? The one for the mains power, not the ones for each backlight supply.

          Comment


            #45
            Re: HP 1955 Monitor Repair Guide

            Originally posted by fiero79 View Post
            I have one of these monitors and I am finding there is a buzzing coming from the inverter board. Near the entry of the 110v power supply. It could be coming from the transformer for the mains power, or the caps that are near the entry of the 110v. Does anyone have a part number for a replacement transformer? The one for the mains power, not the ones for each backlight supply.
            These inverter boards are noted for poor solder joints, if you haven't already I would suggest
            Re- soldering that area.
            Al.
            Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

            Comment


              #46
              Re: HP 1955 Monitor Repair Guide

              Dear Help
              I have a burnt 40T03GP Power Fet and I found some but the second number is Different the ones that blew are 40T03GP and right under that number is 701085. But the ones I can get heve the numbers 40T03GP but the number under that one is 602425 are those fets ok to use. is the socond number of any value I googled the socond number and it never came up.
              Thank for your time
              Ron

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                #47
                Re: HP 1955 Monitor Repair Guide

                Originally posted by Ron K View Post
                Dear Help
                I have a burnt 40T03GP Power Fet and I found some but the second number is Different the ones that blew are 40T03GP and right under that number is 701085. But the ones I can get heve the numbers 40T03GP but the number under that one is 602425 are those fets ok to use. is the socond number of any value I googled the socond number and it never came up.
                Thank for your time
                Ron
                Yes, it's ok to use. The second line is usually manufacturing info like the month/year of manufacture, country of origin, hfe values, etc. Just remember to replace these in pairs, since different dates of manufacture usually indicate different hfe values.

                Also, are you sure the 40T03GP transistors were original to your board? If you look at post #1 of this thread, that board used 2SC5707 transistors. Of course, you might have a different board.....
                Last edited by jetadm123; 01-31-2011, 08:33 PM.

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                  #48
                  Re: HP 1955 Monitor Repair Guide

                  Dear Helper
                  Yes it is a different Monitor and a different board then the Post #1
                  Is this usually the case with the second set of numbers and sometimes even a third
                  set.
                  Thanks for the help greatly apprecaited.
                  Ron

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                    #49
                    Re: HP 1955 Monitor Repair Guide

                    Originally posted by Ron K View Post
                    Dear Helper
                    Yes it is a different Monitor and a different board then the Post #1
                    Is this usually the case with the second set of numbers and sometimes even a third
                    set.
                    Thanks for the help greatly apprecaited.
                    Ron
                    If it is another board and another monitor,what is it doing here (the post)?
                    There are 10 kind of people in this world: those that understand binary, and those who don't.
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                      #50
                      Re: HP 1955 Monitor Repair Guide

                      Thanks Krankshaft.

                      This info saved me a lot of time on a monitor with exactly the problems described.

                      Comment


                        #51
                        Re: HP 1955 Monitor Repair Guide

                        Just a follow up. The monitor is fine now. Recapped for insurance, although there were no signs of cap failure. Root cause was cracked solder joint on ferrite core coil near center 2SC5707s. Took out both 2SC5707s.

                        Touched up all four similar joints. All were hard to get right, although only the cracked one was originally bad. Also found poor joints on AC connector.

                        Thanks again for those who posted this information. It shortened my path a lot.

                        Comment


                          #52
                          Re: HP 1955 Monitor Repair Guide

                          Originally posted by CatalinaWOW View Post
                          Root cause was cracked solder joint on ferrite core coil near center 2SC5707s.
                          As others have mentioned, don't forget to resolder all the inverter transformer pins.
                          --- begin sig file ---

                          If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                          We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                          Please do not post inline and offsite as they slow down the loading of pages.

                          --- end sig file ---

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                            #53
                            Re: HP 1955 Monitor Repair Guide

                            "As others have mentioned, don't forget to resolder all the inverter transformer pins."

                            I resoldered them as advised, although all did appear fine under 15X magnification. Examined all joints on the board with the following conclusions:

                            1. Most reflow joints were good. It appears that a couple of parts had tombstoned and the rework on those was terrible, but probably electrically sound. Redid those for insurance.

                            2. All through hole parts were apparently done manually, by two different operaters. One was good, the other so-so. There were a lot of very good quality joints (including all of the transformers), and a smaller number of joints that ranged from marginally bad to margninally good.

                            Unfortunately I didn't take before pics, and don't think the after pics will help enough be worth opening the monitor up again to take. The bad solder joint was on the inductor adjacent (above-right) to the top right 2SC5707 in Krankshaft's picture identifying the drivers. The solder in the joint was fractured, fracture resulted from inadequate solder fill and poor wetting of the inductor lead. When I resoldered I found it difficult to get proper fill and wetting, it took lots of heat and added flux. True on both leads of both inductors. The pair of drivers ajacent to the bad solder joint were the two dead ones. There is a similar inductor between (slightly to the left) the other two drivers.
                            Last edited by CatalinaWOW; 06-21-2011, 10:31 AM. Reason: Name mispelling and clarification

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                              #54
                              Re: HP 1955 Monitor Repair Guide

                              I have burned Q815 & Q815, pleasetell me what are these transitor?
                              Do someone have the schematic for HP 1955?
                              Thanks in advanced

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                                #55
                                Re: HP 1955 Monitor Repair Guide

                                the monitor has many monitors that use the inverter BQ. usually burn a 4-2SC5707 transistors, the 3 amp fuse or a MOSFET IRFU9024.
                                It is all in net. If the transistors are smd say I do not know what to say.

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                                  #56
                                  Re: HP 1955 Monitor Step By Step

                                  I have a 1955 that I am trying to get working. I have changed all the caps except for the 150uF 450v. I cant see any blown FET's or anything else that might be shorted. What could it be?

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                                    #57
                                    Re: HP 1955 Monitor Step By Step

                                    Originally posted by krantz View Post
                                    I have a 1955 that I am trying to get working. I have changed all the caps except for the 150uF 450v. I cant see any blown FET's or anything else that might be shorted. What could it be?
                                    First describe the type of problem you are having.
                                    A monitor can fail in various ways.
                                    Does it have what we call 2 sec to black?
                                    Dose the power LED come on and recognize a signal?
                                    Can you turn the monitor on and off with the front power switch?
                                    Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                                    Comment


                                      #58
                                      Re: HP 1955 Monitor Step By Step

                                      Originally posted by alexanna View Post
                                      First describe the type of problem you are having.
                                      A monitor can fail in various ways.
                                      Does it have what we call 2 sec to black?
                                      Dose the power LED come on and recognize a signal?
                                      Can you turn the monitor on and off with the front power switch?
                                      The LED comes on and recognizes a signal when i push the power button. It then gives a picture for 0.5 seconds, restarts (also the LED blinks at the restarts) and repeats.

                                      I can turn it off if i hammer the power-button during the restarts.

                                      Comment


                                        #59
                                        Re: HP 1955 Monitor Repair Guide

                                        Do you have a multimeter?It's time to look at some voltages.
                                        Even though this a long thread with photos,It would help to see photos of your power supply front and back.Try to get them focused so we can read the writing on the board
                                        Please use managed attachments to post the photos.
                                        Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                                        Comment


                                          #60
                                          Re: HP 1955 Monitor Repair Guide

                                          Originally posted by alexanna View Post
                                          Do you have a multimeter?It's time to look at some voltages.
                                          Even though this a long thread with photos,It would help to see photos of your power supply front and back.Try to get them focused so we can read the writing on the board
                                          Please use managed attachments to post the photos.
                                          Yes, I do have a multimeter but not sure what component to measure.
                                          Here are some pictures. Ive focused on the components as Krankshaft did.
                                          Attached Files
                                          Last edited by krantz; 10-27-2011, 09:13 AM.

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