Backlight problem on viewSonic VP171b

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  • edfromut
    New Member
    • Nov 2011
    • 3
    #21
    Re: Backlight problem on viewSonic VP171b

    I have the same problem as previous posts, one second delay and then the screen goes black. It looks like I have a shorted transistor (Q5), but I can't identify it. The transistors Q3, Q4, Q5, and Q6 are all the same. They are very small and the only markings on them is "DK" on one line and "QN" underneath it.

    Can anyone identify these transistors?

      Comment

      • PlainBill
        Badcaps Legend
        • Feb 2009
        • 7034
        • USA
        #22
        Re: Backlight problem on viewSonic VP171b

        Originally posted by edfromut
        I have the same problem as previous posts, one second delay and then the screen goes black. It looks like I have a shorted transistor (Q5), but I can't identify it. The transistors Q3, Q4, Q5, and Q6 are all the same. They are very small and the only markings on them is "DK" on one line and "QN" underneath it.

        Can anyone identify these transistors?
        They are 2SC4672, the details are here.

        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

          • edfromut
            New Member
            • Nov 2011
            • 3
            #23
            Re: Backlight problem on viewSonic VP171b

            I replaced Q5 and Q6 and that did the trick. For $5 total it's like brad new. Thanks PlainBill !!

              Comment

              • edfromut
                New Member
                • Nov 2011
                • 3
                #24
                Re: Backlight problem on viewSonic VP171b

                My monitor worked for about 2 weeks then it went blank again. Q5 and Q6 blew again. I replaced them and the monitor worked for about 10 seconds and then they blew again. Do you know what is causing these transistors to blow?

                  Comment

                  • retiredcaps
                    Badcaps Legend
                    • Apr 2010
                    • 9271
                    #25
                    Re: Backlight problem on viewSonic VP171b

                    Originally posted by edfromut
                    Do you know what is causing these transistors to blow?
                    In post #11, I'm fairly sure PlainBill is referring to the Benq boards where the C5707s short because of dodgy/poor soldering on the inverter transformers.

                    Maybe resolder/reflow yours and see.
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                      Comment

                      • PlainBill
                        Badcaps Legend
                        • Feb 2009
                        • 7034
                        • USA
                        #26
                        Re: Backlight problem on viewSonic VP171b

                        There are several causes of the transistors blowing. In addition to the transformers that retiredcaps mentioned, check the timing caps on the inverter (the large blue film cap next to each transformer). Also check for cracked solder joints on the inductor.

                        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.

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