Dell Monitor blinking LED

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  • Pentium4
    CapXon Be Gone
    • Sep 2011
    • 3741
    • USA

    #1

    Dell Monitor blinking LED

    This thing on rare occasion will turn on for a split second, most of the time just have a blinking LED. Fuse F601 and PF751 tested good. 164V across the input cap. Diodes D751 and D761 aren't shorted. I think the problem is either with the caps or the voltage regulator on the main board. That regulator U10 (which reads G061 950T65) acts very strange:

    Pin 1: Bounces between 0.985V - 1.300V
    Pin 2: 0.00V
    Pin 3: Bounces between 0.980V - 1.060V

    Could that be one of the caps next to the regulator? All the caps in this thing are trash (It is a Benq afterall...) The power board has Lelon/Elite and the main board has Lelon/Jamicon/Elite
    Attached Files
  • UniT3d
    Member
    • May 2011
    • 43

    #2
    Re: Dell Monitor blinking LED

    Hmmm .....

    This has so many revisions and yet they have the same common issue.

    If my memory isn't that fuzzy :

    - Check/replace Q739, Q740, Q759, Q760, Q743, Q751
    - Resolder T751, T752, T753, T754
    - Replace all secondary caps

    Comment

    • budm
      Badcaps Legend
      • Feb 2010
      • 40746
      • USA

      #3
      Re: Dell Monitor blinking LED

      Check those 4 inveter tansistors 2SC 5706/5707 for low resistance reding between E and C, and yes, the solder joints
      Which Dell is this?
      http://s807.photobucket.com/albums/yy352/budm/DELL/
      Last edited by budm; 12-17-2012, 03:05 PM.
      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

      • Pentium4
        CapXon Be Gone
        • Sep 2011
        • 3741
        • USA

        #4
        Re: Dell Monitor blinking LED

        It's a Dell E172FPb. All the joints look good on both boards, could they still be bad? When checking the transistors which legs are E and C? Well some are labeled some aren't
        Last edited by Pentium4; 12-17-2012, 03:37 PM.

        Comment

        • Pentium4
          CapXon Be Gone
          • Sep 2011
          • 3741
          • USA

          #5
          Re: Dell Monitor blinking LED

          #1 it gets < 1 Ω, and #2 gets 7.7 Ω
          Attached Files

          Comment

          • budm
            Badcaps Legend
            • Feb 2010
            • 40746
            • USA

            #6
            Re: Dell Monitor blinking LED

            These are the transistors that usually shorted out.
            Attached Files
            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

            • Pentium4
              CapXon Be Gone
              • Sep 2011
              • 3741
              • USA

              #7
              Re: Dell Monitor blinking LED

              All of those between C and E (going both ways) either tested ~7.3Ω or ~287Ω. So I replaced just the secondary caps and now the voltage regulator on the main board is still drastically fluctuating but now the voltages are lower (the low and high) Can that indicate anything?
              Last edited by Pentium4; 12-17-2012, 05:40 PM.

              Comment

              • Lumberjack777
                Badcaps Veteran
                • Dec 2010
                • 464

                #8
                Re: Dell Monitor blinking LED

                Yeah. retiredcaps knows this board very well. It's the "BenQ board". It's almost always one of the inverter transistors circled in red. Or 1 of the 2 circled in blue. And also check the picofuse circled in red.
                Attached Files

                Comment

                • Pentium4
                  CapXon Be Gone
                  • Sep 2011
                  • 3741
                  • USA

                  #9
                  Re: Dell Monitor blinking LED

                  Thanks for the reply. I checked the picofuse and it's good. I gave the readings for the transistors on post #7, does that indicate if any are bad?

                  Comment

                  • retiredcaps
                    Badcaps Legend
                    • Apr 2010
                    • 9271

                    #10
                    Re: Dell Monitor blinking LED

                    Originally posted by Pentium4
                    All of those between C and E (going both ways) either tested ~7.3Ω or ~287Ω.
                    Shorted. They are bad.
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                    • Pentium4
                      CapXon Be Gone
                      • Sep 2011
                      • 3741
                      • USA

                      #11
                      Re: Dell Monitor blinking LED

                      Originally posted by retiredcaps
                      Shorted. They are bad.
                      All of them? Do I need exact replacements? Oh and by the way I tested them still soldered to the board. Did I need to desolder them before I tested them?
                      Last edited by Pentium4; 12-17-2012, 06:39 PM.

                      Comment

                      • retiredcaps
                        Badcaps Legend
                        • Apr 2010
                        • 9271

                        #12
                        Re: Dell Monitor blinking LED

                        Originally posted by Pentium4
                        All of them? Do I need exact replacements? Oh and by the way I tested them still soldered to the board. Did I need to desolder them before I tested them?
                        Desolder all of them and verify out of circuit. We generally recommend they be replaced in pairs.

                        The c5707s are sold as "kits" on ebay because these Benq have known problems.

                        http://www.ebay.com/sch/i.html?_trks...313&_nkw=c5707

                        Resolder all your inverter transformers regardless how they look.
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                        • Pentium4
                          CapXon Be Gone
                          • Sep 2011
                          • 3741
                          • USA

                          #13
                          Re: Dell Monitor blinking LED

                          Originally posted by retiredcaps
                          Desolder all of them and verify out of circuit. We generally recommend they be replaced in pairs.

                          The c5707s are sold as "kits" on ebay because these Benq have known problems.

                          http://www.ebay.com/sch/i.html?_trks...313&_nkw=c5707

                          Resolder all your inverter transformers regardless how they look.
                          Thank you very much for the link! Does it not matter which ones I get on that search list? Okay I will resolder the inverter transformers and I will also replace all of the smaller caps on the primary. For future reference is it the high resistance that indicated those transistors were shorted?

                          Comment

                          • retiredcaps
                            Badcaps Legend
                            • Apr 2010
                            • 9271

                            #14
                            Re: Dell Monitor blinking LED

                            Originally posted by Pentium4
                            Does it not matter which ones I get on that search list?
                            I just buy from sort by lowest price + shipping. A while back I order about 5 "kits" so I have enough to repair anymore Benqs. I picked up 2 Benq's a couple of weeks ago, but I have been busy with other things. I'm sure it will be the "usual" fix.

                            For future reference is it the high resistance that indicated those transistors were shorted?
                            From my 2 seconds guide (post #19)

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

                            Note: a shorted transistor would likely cause a very brief flash of the backlight or no backlight.

                            Mosfets

                            If you have a manual range multimeter, set it to 200 ohms (two hundred). This is for 3 pin ICs only. You can test a mosfet (Q, IC designation) "in circuit" by (power off and unplugged)

                            a) black on pin 1- red on pin 2 - record ohms
                            b) black on pin 1- red on pin 3 - record ohms
                            c) black on pin 2- red on pin 3 - record ohms

                            If any reading is less than 30 ohms you might have shorted mosfet. Remove from circuit and repeat the tests to verify.

                            Some mosfets are more than 3 pins. To test those, identify the part number and search for its datasheet. Once you find the datasheet, the pins will be designated source (S), gate (G), and drain (D). It will probably be documented as S1, S2, G1, G2, D1, D2.

                            Simply test

                            a) black on pin S1- red on pin G1 - record ohms
                            b) black on pin S1- red on pin D1 - record ohms
                            c) black on pin G1- red on pin D1 - record ohms

                            Repeat for the "2" pins. That is S2-G2, S2-D2, G2-D2.
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                            • retiredcaps
                              Badcaps Legend
                              • Apr 2010
                              • 9271

                              #15
                              Re: Dell Monitor blinking LED

                              I forgot to mention that thecapking.com also sells the c5707 and FU9024. He is based in USA.

                              http://thecapking.com/sanyoc5707.html

                              http://thecapking.com/sanyoc5707.html

                              $2 First Class USPS Shipping on All Orders in the US!
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                              Comment

                              • Lumberjack777
                                Badcaps Veteran
                                • Dec 2010
                                • 464

                                #16
                                Re: Dell Monitor blinking LED

                                Originally posted by retiredcaps
                                Resolder all your inverter transformers regardless how they look.
                                Thanks RC. That's vitally important for the repair to last. And I might add that it doesn't mean just touching the joints with a solder iron and remelting the solder. You want to get your wick up there and remove most of the solder a side at a time. And resolder using good quality leaded solder. Then it should last quite awhile.

                                Comment

                                • Pentium4
                                  CapXon Be Gone
                                  • Sep 2011
                                  • 3741
                                  • USA

                                  #17
                                  Re: Dell Monitor blinking LED

                                  Awesome! Thank you very much retiredcaps. I ordered 12 of them so I will report back when I get them and test it out! Yeah I always redo the joints myself. Plus it looks better

                                  Comment

                                  • retiredcaps
                                    Badcaps Legend
                                    • Apr 2010
                                    • 9271

                                    #18
                                    Re: Dell Monitor blinking LED

                                    Link to

                                    http://www.thecapking.com/irfu9024npbf.html

                                    if the FU9024 are shorted.

                                    Did you test these as well?
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                                    • selldoor
                                      Slow Learner
                                      • Dec 2010
                                      • 7870

                                      #19
                                      Re: Dell Monitor blinking LED

                                      I have skimmed through and cant see it - you should also resolder the joints on the capacitors between the 5707s
                                      Please upload pictures using attachment function when ask for help on the repair
                                      http://www.badcaps.net/forum/showthread.php?t=39740

                                      Comment

                                      • Pentium4
                                        CapXon Be Gone
                                        • Sep 2011
                                        • 3741
                                        • USA

                                        #20
                                        Re: Dell Monitor blinking LED

                                        I replaced those transistors, replaced all the caps, and re-soldered all the joints of the 4 inverter transformers. Now it will turn on but I have to use a flashlight to see a picture. Could one of the inverters be bad?
                                        Attached Files

                                        Comment

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