Announcement

Collapse
No announcement yet.

Dell Monitor blinking LED

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    #41
    Re: Dell Monitor blinking LED

    Originally posted by retiredcaps View Post
    So the 12V is there. That 17.26V is unregulated and should drop down once the backlights are on.

    Let's confirm you are measuring the DC voltage on the picofuse correctly.

    1) Put your black probe on a ground screwn.

    2) Put your red probe on one side of the picofuse? What is this reading?

    3) Put your red probe on the other side of the picofuse? What is this reading?
    My apologies, one side is 17.82V and the other is 17.83V

    Comment


      #42
      Re: Dell Monitor blinking LED

      I would check the secondary windings on the inverter transformers even tho
      you dont see any flash. Perhaps also check the primaries but they rarely fail.
      Please upload pictures using attachment function when ask for help on the repair
      http://www.badcaps.net/forum/showthread.php?t=39740

      Comment


        #43
        Re: Dell Monitor blinking LED

        Originally posted by selldoor View Post
        I would check the secondary windings on the inverter transformers even tho
        you dont see any flash. Perhaps also check the primaries but they rarely fail.
        All 4 of them? What pins would I check?

        Comment


          #44
          Re: Dell Monitor blinking LED

          Originally posted by Pentium4 View Post
          All 4 of them? What pins would I check?
          POWER OFF
          On the side with 3 pins first check on one transformer that the two pins close together are in fact joined - resistance 0.00 ohms. then check from either of those to the third pin. (meter on ohms 2000.) post results. Yes for all four transformers.
          If they are ok we can go on to primaries.
          Please upload pictures using attachment function when ask for help on the repair
          http://www.badcaps.net/forum/showthread.php?t=39740

          Comment


            #45
            Re: Dell Monitor blinking LED

            Originally posted by selldoor View Post
            POWER OFF
            On the side with 3 pins first check on one transformer that the two pins close together are in fact joined - resistance 0.00 ohms. then check from either of those to the third pin. (meter on ohms 2000.) post results. Yes for all four transformers.
            If they are ok we can go on to primaries.
            All the adjacent pins tested good, and when checking to the 3rd pin they were all ~200Ω

            Comment


              #46
              Re: Dell Monitor blinking LED

              They are probably ok then - I have been trying to find out what it should be 200 ohms seems low but they are all different.
              In post 19 I mentioned resoldering the caps near the 5707s and you rplied that you had replaced all the caps. Those ones are not usually replaced so I am just checking that you have resoldered them C735 C755 C754 C734.
              Please upload pictures using attachment function when ask for help on the repair
              http://www.badcaps.net/forum/showthread.php?t=39740

              Comment


                #47
                Re: Dell Monitor blinking LED

                Sorry - but I have to ask - you are plugging the leads from the lamps into the board
                when you are testing (I have known it heheh have even done it!!)
                Please upload pictures using attachment function when ask for help on the repair
                http://www.badcaps.net/forum/showthread.php?t=39740

                Comment


                  #48
                  Re: Dell Monitor blinking LED

                  Originally posted by selldoor View Post
                  They are probably ok then - I have been trying to find out what it should be 200 ohms seems low but they are all different.
                  In post 19 I mentioned resoldering the caps near the 5707s and you rplied that you had replaced all the caps. Those ones are not usually replaced so I am just checking that you have resoldered them C735 C755 C754 C734.
                  Think the primary one is okay too then? And alright I will resolder those caps. I meant I replaced all of the lytics

                  Originally posted by selldoor View Post
                  Sorry - but I have to ask - you are plugging the leads from the lamps into the board
                  when you are testing (I have known it heheh have even done it!!)
                  Haha, I understand. Yes I have been, double check every time

                  Edit: Resoldered, no luck yet Thanks for your continued help!
                  Last edited by Pentium4; 01-10-2013, 02:33 PM.

                  Comment


                    #49
                    Re: Dell Monitor blinking LED

                    By the way, while checking this monitor, do you have the VGA cable connected to a running PC?
                    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


                      #50
                      Re: Dell Monitor blinking LED

                      Originally posted by budm View Post
                      By the way, while checking this monitor, do you have the VGA cable connected to a running PC?
                      Yeah, and I can see the desktop with a flashlight

                      Comment


                        #51
                        Re: Dell Monitor blinking LED

                        Let's get back to basics here.

                        1) Is the power LED on or off?

                        2) Is the power LED blinking or solid?

                        3) What is the DC voltage on U10 (logic board)? Report all 3 pins.

                        4) When you press the on/off button does BL_ON = pin 2 (connector) change from 0.0V to 3.0V DC? See

                        https://www.badcaps.net/forum/showpo...4&postcount=27

                        Remember that the main/logic board needs to signal BL_ON high in order for the backlights to come on.

                        In post 31, you only measured 5 out of the 10 pins. BTW, I prefer text based answers rather than paint. It helps with people searching in the future and makes it easier for us to read.

                        5) There are 4 blue tuning caps next to the ccfl connectors. I can see C736 and C756. With power off, measure the resistance across the legs of all 4 caps. They should all read open circuit on the higest resistance range.
                        Last edited by retiredcaps; 01-11-2013, 01:54 AM.
                        --- 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


                          #52
                          Re: Dell Monitor blinking LED

                          Originally posted by retiredcaps View Post
                          Let's get back to basics here.

                          1) Is the power LED on or off?

                          2) Is the power LED blinking or solid?

                          3) What is the DC voltage on U10 (logic board)? Report all 3 pins.

                          4) When you press the on/off button does BL_ON = pin 2 (connector) change from 0.0V to 3.0V DC? See

                          https://www.badcaps.net/forum/showpo...4&postcount=27

                          Remember that the main/logic board needs to signal BL_ON high in order for the backlights to come on.

                          In post 31, you only measured 5 out of the 10 pins. BTW, I prefer text based answers rather than paint. It helps with people searching in the future and makes it easier for us to read.

                          5) There are 4 blue tuning caps next to the ccfl connectors. I can see C736 and C756. With power off, measure the resistance across the legs of all 4 caps. They should all read open circuit on the higest resistance range.
                          1) On

                          2) Solid (And it will power off when I hit the power button)

                          3)
                          Pin 1 = 3.26V
                          Pin 2 = 0.00V
                          Pin 3 = 2.50V

                          4) Yes, it goes to 3.16V (Okay no more paint ) Do you want exact results on the other 5? I don't remember which is which but they either measured 3.3V or 5V

                          5) They all tested open

                          Comment


                            #53
                            Re: Dell Monitor blinking LED

                            More things to check - with power off R765 (lift one leg) and , with power on check voltage across IC751 IF it is a (TL1451AC) then pin’s 8~ (ground) and 9~ (+15Vdc) there should be 15Vdc. Need to be careful pins are small and very close. Slip and its gone!!!.



                            EDIT Have you anything to check the ccfl bulbs on - so we know if they are going to work
                            eventually.
                            Last edited by selldoor; 01-11-2013, 12:36 PM.
                            Please upload pictures using attachment function when ask for help on the repair
                            http://www.badcaps.net/forum/showthread.php?t=39740

                            Comment


                              #54
                              Re: Dell Monitor blinking LED

                              Okay I will do that just to be sure, black probe on pin 8 and red probe on pin 9? And just curious, why R765 specifically?

                              Comment


                                #55
                                Re: Dell Monitor blinking LED

                                Originally posted by Pentium4 View Post
                                Okay I will do that just to be sure, black probe on pin 8 and red probe on pin 9? And just curious, why R765 specifically?
                                Yes, black probe on pin 8 and red probe on pin 9.

                                Apparently IC751 contains an oscillator circuit and frequency is controlled by C765 (470p 50v) and R765 - It is a 1% tolerance resistor and is critical for the circuit ( or I dont know - have just read it somewhere. )
                                Please upload pictures using attachment function when ask for help on the repair
                                http://www.badcaps.net/forum/showthread.php?t=39740

                                Comment


                                  #56
                                  Re: Dell Monitor blinking LED

                                  So apparently R765 is a 120Ω resistor but it only measured out to 9.96Ω and testing the TL1451ACN, I didn't get any DC Voltage on pin 9

                                  Comment


                                    #57
                                    Re: Dell Monitor blinking LED

                                    Originally posted by Pentium4 View Post
                                    So apparently R765 is a 120Ω resistor but it only measured out to 9.96Ω and testing the TL1451ACN, I didn't get any DC Voltage on pin 9
                                    10 ohms may be correct what are the band colours
                                    Please upload pictures using attachment function when ask for help on the repair
                                    http://www.badcaps.net/forum/showthread.php?t=39740

                                    Comment


                                      #58
                                      Re: Dell Monitor blinking LED

                                      Originally posted by selldoor View Post
                                      10 ohms may be correct what are the band colours
                                      Brown, Red, Black, Black, Brown

                                      Unless I did it backwards

                                      Comment


                                        #59
                                        Re: Dell Monitor blinking LED

                                        Perhaps it was for a different board/revision those colours are correct for
                                        for that resistance 120ohms - you did have it lifted?

                                        If you could post a clearer picture of the board so I can see the colours
                                        a bit better I can do more looking tho it will be tomorrow now.

                                        Maybe retiredcaps will come up with something later on regarding the results of the test you did for him.
                                        Please upload pictures using attachment function when ask for help on the repair
                                        http://www.badcaps.net/forum/showthread.php?t=39740

                                        Comment


                                          #60
                                          Re: Dell Monitor blinking LED

                                          Originally posted by Pentium4 View Post
                                          I didn't get any DC Voltage on pin 9
                                          If you don't have any voltage on pin 9, it could be one of two things:

                                          1) IC is bad. With power off, see if VCC (pin 9) is shorted to GND (pin 8). Report your ohms reading.

                                          2) The circuit path to pin 9 is bad. Take your multimeter and put it into continuity mode. Put one probe on pin 9 and the other probe on components that might have continuity to pin 9.

                                          For example, pin 9 might have continuity to C764 and R787. You can either check those components to see if they are okay or check the DC voltage on them.

                                          You know PF751 has 17V DC. You are just trying to find out why it doesn't reach pin 9. For example, an open resistor would stop 17V from getting to pin 9.

                                          PS. Note to future readers, here is where picture orientation matters in post #1. The top power board is "right side up". The backside of the power board is "upside down". This forces regulars to download the picture, rotate it, etc (i.e. more work on our part).
                                          --- 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

                                          Working...
                                          X