HP no backlight

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  • davg
    Badcaps Veteran
    • Sep 2008
    • 536
    • Canada

    #41
    Re: HP no backlight

    Thanks budm with black prob on GRN screw the read as follows pin 1- 0L pin 2- 0L pin 3- Grn 0
    pin 4- 0L pin 5 0L pin 6- 93.0 ohms pin 7-119 ohms pin 8 .780 mohms
    Jetadm123 R105 22ohms C102 reads 16.30 mohms one way 0L the other Un plugged no power
    Plugged in power on connected to running computer R102 reads 5 v one side 3.2 v other side and C102 reads .9volts one side and 0 other side and across C102 is .9 volts
    Last edited by davg; 11-06-2012, 06:14 PM.

    Comment

    • jetadm123
      Badcaps Legend
      • Feb 2010
      • 2169

      #42
      Re: HP no backlight

      Can you read C102 again. It's "+" leg is sharing VDD and should also read 3.2V.
      Last edited by jetadm123; 11-06-2012, 06:44 PM.

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #43
        Re: HP no backlight

        OK, is pin 8 = 0.780 Ohm or 780 Ohms? if it is 0.780 Ohms, then there is short circuit around pin 8.
        VDD pin also seems low at less than 100 Ohms.
        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

        • davg
          Badcaps Veteran
          • Sep 2008
          • 536
          • Canada

          #44
          Re: HP no backlight

          pin 8 is reading 0.780 megohms

          Comment

          • jetadm123
            Badcaps Legend
            • Feb 2010
            • 2169

            #45
            Re: HP no backlight

            If you're still seeing .9V across C102, it sounds like it's shorted to ground. I would try changing it to see what happens.

            Comment

            • davg
              Badcaps Veteran
              • Sep 2008
              • 536
              • Canada

              #46
              Re: HP no backlight

              The voltage across C102 is 3.91v Grn to + 3.91 and Grn to - 0 v I have no idea where the first reading came from I thought I may have read C105 but there is 2.5 v across that one. sorry

              Comment

              • jetadm123
                Badcaps Legend
                • Feb 2010
                • 2169

                #47
                Re: HP no backlight

                Here are my thoughts so far:

                I looked at the datasheet for the OZ9938 and the min VDD is 4.5V. If the OZ9930 is similar, then your VDD is too low. I'm wondering if that .6V difference is enough to cause it not to operate?

                When you said you changed all the caps, do you also change C102? If not, try changing it and see what happens.

                C102 appears to be a filter cap to protect VDD against voltage spikes/noise. If you don't have a spare cap for C102, for testing purposes, leave C102 off the board and see if VDD increases. If not, then something could be wrong with the OZ9930.

                Comment

                • davg
                  Badcaps Veteran
                  • Sep 2008
                  • 536
                  • Canada

                  #48
                  Re: HP no backlight

                  Thanks jetadm123 yes I did replace C102. I could remove it?? I am getting slight a humming on the board as I indicated earlier and I can't tell where it is coming from but it is close to one of the transformer. T101 or T102. What does that indicate? Should that be a concern?

                  Comment

                  • jetadm123
                    Badcaps Legend
                    • Feb 2010
                    • 2169

                    #49
                    Re: HP no backlight

                    As retiredcaps mentioned earlier, the lack of VDD reading around 5V could indicate a possible short. When you soldered in the new caps in the inverter section, did you make sure that there were no solder bridges that might cause a short?

                    Also, if you continue going through the flowchart, you'll see that very few of your voltage readings meet the suggested values for I101. It's understood that since you don't have a scope, you cannot perform some of the steps.

                    Comment

                    • budm
                      Badcaps Legend
                      • Feb 2010
                      • 40746
                      • USA

                      #50
                      Re: HP no backlight

                      I would suggest you to recheck all your works just to be sure.
                      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

                      • davg
                        Badcaps Veteran
                        • Sep 2008
                        • 536
                        • Canada

                        #51
                        Re: HP no backlight

                        Thanks guys I will go over the board again to be sure there are no shorts caused by my soldering. I will report back

                        Comment

                        • davg
                          Badcaps Veteran
                          • Sep 2008
                          • 536
                          • Canada

                          #52
                          Re: HP no backlight

                          I have carefully looked over the board and I am unable to see any thing that looks like a grn? I did discover a lifted trace on C122 but it is still contacting. Not sure where I go from here?

                          Comment

                          • jetadm123
                            Badcaps Legend
                            • Feb 2010
                            • 2169

                            #53
                            Re: HP no backlight

                            A lifted pad/trace on a circuit board is considered unreliable and should be repaired using point to point wiring. Solder one end of a wire to the lifted lead of C122 and the other end to solder a pad at the other end of that trace.

                            Comment

                            • davg
                              Badcaps Veteran
                              • Sep 2008
                              • 536
                              • Canada

                              #54
                              Re: HP no backlight

                              Thanks jetadm123 it appears from the schematic that the plus side of C122 (which was lifted) goes to pin 8 of Q104 so should I connect these two points?
                              Attached Files

                              Comment

                              • jetadm123
                                Badcaps Legend
                                • Feb 2010
                                • 2169

                                #55
                                Re: HP no backlight

                                Actually, connections are shown using a red dot. Therefore, the "+" side of C122 is connected to pin 3 of Q104.

                                Comment

                                • davg
                                  Badcaps Veteran
                                  • Sep 2008
                                  • 536
                                  • Canada

                                  #56
                                  Re: HP no backlight

                                  Thanks jetadm123 made the connection + side of C122 to pin 3 Q104 no difference?

                                  Comment

                                  • jetadm123
                                    Badcaps Legend
                                    • Feb 2010
                                    • 2169

                                    #57
                                    Re: HP no backlight

                                    Well, I'm stumped. I can't think of anything else.

                                    Comment

                                    • davg
                                      Badcaps Veteran
                                      • Sep 2008
                                      • 536
                                      • Canada

                                      #58
                                      Re: HP no backlight

                                      Ya I know what you mean Thanks pal appreciate the support from yourself, budm, retiredcaps and others on this great site. I did keep a file on the test conducted and may revisit it sometime down the road. In the meantime I have several of these that I will revisit, some with the same symptoms.

                                      Comment

                                      • budm
                                        Badcaps Legend
                                        • Feb 2010
                                        • 40746
                                        • USA

                                        #59
                                        Re: HP no backlight

                                        Any way, this is the resistance reading of the OZ9930 with the help of lestr:
                                        https://www.badcaps.net/forum/showth...771#post280771
                                        So I am not sure which reading is correct, yours or lestr.
                                        Last edited by budm; 11-08-2012, 11:36 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

                                        • retiredcaps
                                          Badcaps Legend
                                          • Apr 2010
                                          • 9271

                                          #60
                                          Re: HP no backlight

                                          @davg. If you are game, I circled a number of diodes in yellow and transistors in red. See if any of them are shorted.

                                          It should take you about 10 minutes to test them all.
                                          Attached Files
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                                          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

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