A1286 820-2915b chime ok, but no image no bklight

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  • marce002
    Badcaps Veteran
    • May 2018
    • 316
    • Argentine
    #1

    A1286 820-2915b chime ok, but no image no bklight

    Hello

    I have this a1286 with minor water damage, after cleaned ISL area turns on and chimes , load os but: no image no backlight.... LCD_PWR_EN is 0vol ..
    I have done gmux bypass to many a1286s with gpu issues, so though this would be the case. routed jumpers to avoid the gpu and removed resistor r8911 as usual to disable ati gpu... but still no LCD_PWR_EN signal...

    what can be going on to not have LCD_PWR_EN enabled? i do have 3.3v in pin 4 at lcd connector but not pins 2,3, because u9000 is not enabled by this missing LCD_PWR_EN

    thanks in advance

    pd i did not remove gmuch chi only bypassed in site like this img:

    Last edited by marce002; 05-13-2022, 03:32 PM.
    Marcelo J
    Tags: None
    • mon2
      Badcaps Legend
      • Dec 2019
      • 13940
      • Canada
      #2
      Re: A1286 820-2915b chime ok, but no image no bklight

      What is the voltage of R9678, pin # 1 ?
      Attached Files

        Comment

        • marce002
          Badcaps Veteran
          • May 2018
          • 316
          • Argentine
          #3
          Re: A1286 820-2915b chime ok, but no image no bklight

          Hi mon it is 8.2mV at #1 and 2.66V at #2.. resistor is in range
          Marcelo J

            Comment

            • mon2
              Badcaps Legend
              • Dec 2019
              • 13940
              • Canada
              #4
              Re: A1286 820-2915b chime ok, but no image no bklight

              Check the resistance to ground of LCD_PWR_EN pin. Any liquid damage in this area ? Trace is ok from source (U9600) to target ?

                Comment

                • marce002
                  Badcaps Veteran
                  • May 2018
                  • 316
                  • Argentine
                  #5
                  Re: A1286 820-2915b chime ok, but no image no bklight

                  it is 8.2kohm and traces are ok there around...

                  remember that i have a mod jumper from #1 of r9678 (lcd_pwr_en) to R2015 pin 1 (lvds_ig_panel_pwr)
                  Last edited by marce002; 05-13-2022, 04:35 PM.
                  Marcelo J

                    Comment

                    • marce002
                      Badcaps Veteran
                      • May 2018
                      • 316
                      • Argentine
                      #6
                      Re: A1286 820-2915b chime ok, but no image no bklight

                      R2015 is the source for my lcd_pwr_en after my mod.... is it? .. which in fact should be 100kohm and i have it at around 8kohm... mmm
                      Marcelo J

                        Comment

                        • marce002
                          Badcaps Veteran
                          • May 2018
                          • 316
                          • Argentine
                          #7
                          Re: A1286 820-2915b chime ok, but no image no bklight

                          bad pch?
                          Marcelo J

                            Comment

                            • mon2
                              Badcaps Legend
                              • Dec 2019
                              • 13940
                              • Canada
                              #8
                              Re: A1286 820-2915b chime ok, but no image no bklight

                              But you don't have an image?

                                Comment

                                • marce002
                                  Badcaps Veteran
                                  • May 2018
                                  • 316
                                  • Argentine
                                  #9
                                  Re: A1286 820-2915b chime ok, but no image no bklight

                                  nop no image no backlight but do have brain ...replaced that resistor and after soldered in it is 8kohm so in circuit resistor parallel afects messurement.
                                  Marcelo J

                                    Comment

                                    • mon2
                                      Badcaps Legend
                                      • Dec 2019
                                      • 13940
                                      • Canada
                                      #10
                                      Re: A1286 820-2915b chime ok, but no image no bklight

                                      Do you get external video?

                                        Comment

                                        • marce002
                                          Badcaps Veteran
                                          • May 2018
                                          • 316
                                          • Argentine
                                          #11
                                          Re: A1286 820-2915b chime ok, but no image no bklight

                                          please understand me.. i ve just made a bypass in order to fix gpu issues and that excludes external monitor usage
                                          Marcelo J

                                            Comment

                                            • marce002
                                              Badcaps Veteran
                                              • May 2018
                                              • 316
                                              • Argentine
                                              #12
                                              Re: A1286 820-2915b chime ok, but no image no bklight

                                              fixed it was bad corrupted efi bios so if you have chime but lcd pwr on signal not enabled might NOT be a bad pch or bad connector screen or coils around... thks mon
                                              Last edited by marce002; 05-17-2022, 05:16 PM.
                                              Marcelo J

                                                Comment

                                                • mon2
                                                  Badcaps Legend
                                                  • Dec 2019
                                                  • 13940
                                                  • Canada
                                                  #13
                                                  Re: A1286 820-2915b chime ok, but no image no bklight

                                                  Well done! Thanks for the update.

                                                    Comment

                                                    • gurangax
                                                      Member
                                                      • Apr 2020
                                                      • 34
                                                      • Malaysia
                                                      #14
                                                      Re: A1286 820-2915b chime ok, but no image no bklight

                                                      Originally posted by marce002
                                                      fixed it was bad corrupted efi bios so if you have chime but lcd pwr on signal not enabled might NOT be a bad pch or bad connector screen or coils around... thks mon
                                                      Thanks for tips. I managed to fix mine same problem. flashed with other firmware and it worked.

                                                        Comment

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