Hp 1940 flicker

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  • terminatorX
    Senior Member
    • Feb 2012
    • 63

    #1

    Hp 1940 flicker

    I have one hp 1940 (Benq 48.L1G02.A00) that when plugged to power starts flicker rather rapidly and just keeps doing that. To mention not connected to PC. The power led is on.
    It's not originally my screen so I can't really say anymore in the symtoms department and I removed the power board from the inside now. Nothing really seems to be blown or damaged, no bulging of capacitators. Is it the usual C5707 transistor problem?


  • selldoor
    Slow Learner
    • Dec 2010
    • 7870

    #2
    Re: Hp 1940 flicker

    We cant tell if a transistor is faulty especially when we cant see it.

    I suggest you read this https://www.badcaps.net/forum/showthread.php?t=14068 , read the 2 secs to black guide carry out the tests mentioned and post your results.
    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

      #3
      Re: Hp 1940 flicker

      So i did some small reading and the guide seems to be really good!
      I'm to tired to read it through and eventually do some testing..guess i'll do that later. But I tested the screen more properly just to make it easier for you to do some speculation. The flicker mode is more like...there is a picture of the desktop and it flashes quickly and then it's like one second delay (black screen) and then the same flash and I had it on for like 20 seconds so it seems it goes on like that indefinitely. The power led stays lit and it's possible to hold the button down to power down the monitor.
      Attached Files

      Comment

      • retiredcaps
        Badcaps Legend
        • Apr 2010
        • 9271

        #4
        Re: Hp 1940 flicker

        You must, mandatory, resolder or reflow every solder joint circled in red regardless whether it looks good or not.

        The Benq boards all suffer from bad/poor solder joints.

        Retest after resolder/reflow.
        Attached Files
        --- 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 ---

        Comment

        • Hunt
          Member
          • Jun 2009
          • 31

          #5
          Re: Hp 1940 flicker

          My HP 1940 for a long time made a loud click now and then, but the screen never showed signs of a problem; in fact I did not realise it was the screen till I move office and the only common item was the screen.

          The screen is slow to shutdown the monitor dialogue that says what connection it has to the PC. So much so that it is an annoyance as I have to move the page around to see what is under/obscured by the dialogue.

          Now the screen has developed a flickering on and off fault similar to the title of this thread.

          The flicker is not occurring at this moment but seems to be related to the amount of time the monitor is switched on.

          Since it is my second monitor that is used as an electronic document holder; I sometimes turn it off when not needed. Switching the screen back on seems to trigger the flicker.

          Does all the above sound like a bad cap fault?

          P.S. is it ok to add to this thread or should I have created another one?


          (Thanks to this forum, I am still using a ViewSonic that I repaired a year ago)

          Comment

          • PlainBill
            Badcaps Legend
            • Feb 2009
            • 7034
            • USA

            #6
            Re: Hp 1940 flicker

            Originally posted by Hunt
            My HP 1940 for a long time made a loud click now and then, but the screen never showed signs of a problem; in fact I did not realise it was the screen till I move office and the only common item was the screen.

            The screen is slow to shutdown the monitor dialogue that says what connection it has to the PC. So much so that it is an annoyance as I have to move the page around to see what is under/obscured by the dialogue.

            Now the screen has developed a flickering on and off fault similar to the title of this thread.

            The flicker is not occurring at this moment but seems to be related to the amount of time the monitor is switched on.

            Since it is my second monitor that is used as an electronic document holder; I sometimes turn it off when not needed. Switching the screen back on seems to trigger the flicker.

            Does all the above sound like a bad cap fault?

            P.S. is it ok to add to this thread or should I have created another one?


            (Thanks to this forum, I am still using a ViewSonic that I repaired a year ago)
            The flickering could be due to bad caps. The only way to find out is to open the monitor up.

            I prefer to see all problems with a single monitor in a single thread. This gets confusing only if two unrelated faults are being troubleshot at the same time for two people.

            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

              #7
              Re: Hp 1940 flicker

              You must, mandatory, resolder or reflow every solder joint circled in red regardless whether it looks good or not.

              The Benq boards all suffer from bad/poor solder joints.
              Hah interesting. Not sure about the reflow part. Should I get a heating gun for that? If so what is the best temperature? If I do decide to just resolder,
              I think it would be smart testing the transistors outside the board maybe. If I would use my DMM what would you expect for ohms for working transistors?
              Forgott I have I diode checker but not sure what to expect...
              Maybe good to compare between these to check the DMM ability...

              Comment

              • selldoor
                Slow Learner
                • Dec 2010
                • 7870

                #8
                Re: Hp 1940 flicker

                I would just re solder the joints, you can add a little solder and flux to get the process going rather than just working on the old solder. Try and practice on something first if you have any old boards.

                Just test the Transistors in position as follows ( and as you were going to read?):
                2) Shorted Transistors/MOSFETs
                ------------------------------------

                On some LCD brands (example: Benq) the transistors (C5707) are sometimes shorted. Transistors are usually marked with a "Q" designation.

                If you have a manual range multimeter, set it to 200 ohms (two hundred). You can test for shorted transistors "in circuit" (with power off and unplugged)

                a) put black probe on pin 1 and red probe on pin 2 - read/record ohm
                b) put black probe on pin 1 and red probe on pin 3 - read/record ohm
                c) put black probe on pin 2 and red probe on pin 3 - read/record ohm

                If any ohm reading is less than 30 ohm you might have shorted transistor. Remove the transistor and repeat the tests out of circuit to verify.

                Only remove if any reading is less than 30ohm
                Post the results and someone will say if they are good or not.

                The picture of the back of your board is not really clear enough - can you retake and repost it
                Last edited by selldoor; 02-13-2012, 01:13 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

                  #9
                  Re: Hp 1940 flicker

                  Really good help thanks!
                  Is there a particullar part of the board you want to see? Maybe I can concentrate in doing that part more clearer?

                  Comment

                  • selldoor
                    Slow Learner
                    • Dec 2010
                    • 7870

                    #10
                    Re: Hp 1940 flicker

                    Just the whole board - there are members on here who can spot faults that people with the boards in their hands cant see. It needs to be a bit sharper than the one you posted and without the blue dots? I was looking at the top left where there is some browning. If anyone wants a close up of a section they will ask.
                    Please upload pictures using attachment function when ask for help on the repair
                    http://www.badcaps.net/forum/showthread.php?t=39740

                    Comment

                    • Hunt
                      Member
                      • Jun 2009
                      • 31

                      #11
                      Re: Hp 1940 flicker

                      Originally posted by terminatorX
                      I have one hp 1940 (Benq 48.L1G02.A00) that when plugged to power starts flicker rather rapidly and just keeps doing that. To mention not connected to PC. The power led is on.
                      It's not originally my screen so I can't really say anymore in the symtoms department and I removed the power board from the inside now. Nothing really seems to be blown or damaged, no bulging of capacitators. Is it the usual C5707 transistor problem?
                      Hi TerminiatorX,
                      How did you get at the circuit boards?

                      I have the plastic back and front off and the screws holding the rectangular box with the powers socket and other sockets removed but the rectangular box will only lift a few millimetres.

                      It seems to now be held in place by a heat sink that is attracted to the removable box ;(

                      If I undo the other screws that hold the flat metal plate to the screen there are two short wires that go up to the metal box I am trying to remove.

                      The above seems like catch22 how did gain access to the board and caps?

                      Comment

                      • Hunt
                        Member
                        • Jun 2009
                        • 31

                        #12
                        Re: Hp 1940 flicker

                        Well I lifted the tape off the wires holding the bundle to the panel going to the long connector at the top of the panel and removed the long slim plug.
                        That gained me nothing.
                        Going back to the rectangular metal box and peering in side to see how the heat sink was attached; the rectangular box fell off! I was not using enough force it seems, as the only thing holding the box on was some single sided adhesive tape that is attached to the (power transistors?).

                        Now I can see if any caps are bulging

                        Comment

                        • terminatorX
                          Senior Member
                          • Feb 2012
                          • 63

                          #13
                          Re: Hp 1940 flicker

                          Hello Hunt!

                          Was just about to try to help you Hunt =) Se you managed it yourself.
                          As I understand you are far from solving the problem buy just looking at bulging caps.

                          Over to my pictures. It's not that easy doing clear views since there is alot of reflection...
                          Attached Files

                          Comment

                          • Hunt
                            Member
                            • Jun 2009
                            • 31

                            #14
                            Re: Hp 1940 flicker

                            Here are my photos of my faulty board...
                            Attached Files

                            Comment

                            • Hunt
                              Member
                              • Jun 2009
                              • 31

                              #15
                              Re: Hp 1940 flicker

                              Originally posted by Hunt
                              Here are my photos of my faulty board...
                              I cannot see any bulging caps so I am now not sure how to progress

                              What should I do next?

                              Thanks.

                              P.S. I had to crop photos to get them to upload; hope they are ok.

                              Comment

                              • Hunt
                                Member
                                • Jun 2009
                                • 31

                                #16
                                Re: Hp 1940 flicker

                                Originally posted by terminatorX
                                Hello Hunt!

                                Was just about to try to help you Hunt =) Se you managed it yourself.
                                As I understand you are far from solving the problem buy just looking at bulging caps.

                                Over to my pictures. It's not that easy doing clear views since there is alot of reflection...
                                You board looks the same as mine with the same hot areas.

                                Comment

                                • selldoor
                                  Slow Learner
                                  • Dec 2010
                                  • 7870

                                  #17
                                  Re: Hp 1940 flicker

                                  Have you both resoldered the power boards?
                                  There is little point in doing much else until you do.

                                  Can either of you make out the part number on IC701 -both show some signs
                                  of overheating.

                                  @hunt - Can you update your profile so we know where you are. Can you check the voltage on the large capacitor. CAREFULLY. High Voltage
                                  If you look at the Terminator X post for the HP1955 it tells you how to do it.
                                  Please upload pictures using attachment function when ask for help on the repair
                                  http://www.badcaps.net/forum/showthread.php?t=39740

                                  Comment

                                  • Hunt
                                    Member
                                    • Jun 2009
                                    • 31

                                    #18
                                    Re: Hp 1940 flicker

                                    Originally posted by selldoor
                                    Have you both resoldered the power boards?
                                    There is little point in doing much else until you do.
                                    I am reluctant to do any re-soldering since I cannot see any section that looks cracked by heating up and cooling down or any signs of dry joints when observed with a jeweller's eyeglass.

                                    Sorry just seen the bit about joints Circled in red!

                                    Originally posted by selldoor
                                    Can either of you make out the part number on IC701 -both show some signs
                                    of overheating.
                                    The IC seems to have a logo of ST at the top left to the right of that there is a circle that contains a lower case e and a number 3

                                    In the middle on the left there is a circle that contains characters F2 that are oriented (-90deg) bottom to top, to the right of that there is L117

                                    At the bottom of the chip could be the characters GK 16053
                                    The G could be a 6.
                                    The K is definitely K.
                                    After that the letters are like tea leaves and could be anything that my brain comes up with
                                    Last edited by Hunt; 02-18-2012, 03:41 AM.

                                    Comment

                                    • Hunt
                                      Member
                                      • Jun 2009
                                      • 31

                                      #19
                                      Re: Hp 1940 flicker

                                      Originally posted by retiredcaps
                                      You must, mandatory, resolder or reflow every solder joint circled in red regardless whether it looks good or not.

                                      The Benq boards all suffer from bad/poor solder joints.

                                      Retest after resolder/reflow.
                                      Resolder all these top side (main component board side) solder joints yes?

                                      Comment

                                      • Hunt
                                        Member
                                        • Jun 2009
                                        • 31

                                        #20
                                        Re: Hp 1940 flicker

                                        Originally posted by Hunt
                                        Resolder all these top side (main component board side) solder joints yes?
                                        I've assumed yes; all upper mini transformers (what are they and what do they do?) have had there connections resoldered.

                                        Voltage accross C605 is...
                                        Power to monitor with switch off 326V
                                        Monitor switched on 320V
                                        Monitor left on and screen blanked 328V

                                        Now going to replace all metal work and attach to stand without plastic case to do longer test to see if flicker has gone.

                                        Comment

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