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Asus X555L backlight shuts off when on battery

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    #21
    Re: Asus X555L backlight shuts off when on battery

    Hi guys, same issue here (I think)
    so far I have noticed two things:

    1. BL_EN signal going to the LCD is 2.6v not sure if this is normal nevertheless backlight comes on when plugging the charger.

    2. AC_BAT_SYS going to LCD when on charger is 19V and after disconnecting the charger it drop to 7.6v (battery voltage). My assumption is that this is the main issue for the backlight not turning on. I would expect the voltage to be in range 12v-19v

    Not realy sure where to go from here? Charge controller IC?

    Comment


      #22
      Re: Asus X555L backlight shuts off when on battery

      Just had a look at LCD panel specification that I have (Innolux N156BGE-L31)
      Basically all the signals going to the pannel are correct and within the specification.

      From specification:
      1. BL_EN - backlight enabled voltage range 2.4-3.6
      2. Pin38, Pin39, Pin40 - backlight voltage range 6v-21v

      So... it must be that LCD logic board that is faulty. Could be the backlight DC boost circuit. I will be checking that today

      Comment


        #23
        Re: Asus X555L backlight shuts off when on battery

        It would be interesting to see how/if you manage to solve this issue. This was slightly before I got really into component-level board repairs, so I lacked the required skills and knowledge to work out stuff like this on my own.
        Wattevah...

        Comment


          #24
          Re: Asus X555L backlight shuts off when on battery

          Originally posted by sakalaz View Post
          Just had a look at LCD panel specification that I have (Innolux N156BGE-L31)
          Basically all the signals going to the pannel are correct and within the specification.

          From specification:
          1. BL_EN - backlight enabled voltage range 2.4-3.6
          2. Pin38, Pin39, Pin40 - backlight voltage range 6v-21v

          So... it must be that LCD logic board that is faulty. Could be the backlight DC boost circuit. I will be checking that today
          Just replace the coil(marked 100) near backlit IC on led panel. Though weird but works. had this same issue on asus.

          See my thread
          https://www.badcaps.net/forum/showthread.php?t=76823
          Last edited by mcplslg123; 09-13-2019, 07:55 AM.

          Comment


            #25
            Re: Asus X555L backlight shuts off when on battery

            Hm...wonder if it works on this model too. Guess it depends on what panel you get in your laptop, since I imagine they may differ even between identical models.
            Wattevah...

            Comment


              #26
              Re: Asus X555L backlight shuts off when on battery

              Yes, it seems to be same on all the Asus xx55y models with this fault. It took two hours of research surfing russian forums to find out about it. (And I don't even speak russian )
              Last edited by RethoricalCheese; 09-17-2019, 02:41 PM.

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                #27
                Re: Asus X555L backlight shuts off when on battery

                So I went through the backlight circuit without having a datasheet for CM509A chip and couldn't find anything obviously wrong...

                Just replacing the coil sounds not very convincing. Coils are passive components so it is uncommon for them to go bad unless they run hot or windings get shorted. Those LCDs that get "fixed" by replacing the coild could most likely be the cause of heat applied to driver chip or the diode near it (remember graphics chips, tantulum capacitors...) Nontheless I will try replacing the coil as a last try.

                Just found someone stating that MP3388 is a direct alternative for CM509A. I will have another galnce at the board now with this information at hand.

                Datasheet for MP33388 https://cdn.badcaps-static.com/pdfs/...f57cd8ef3f.pdf

                Orderd an inductance meter from aliexpress and a pair of CM509A and MP3388 chips to play with.
                This coil is 10 uH I think? Will be interresting to measure it

                so next steps:
                1. Take the coil off and measure it
                2. Change a backlight driver chip to new one
                3. Change a backlight driver chip to alternative (MP3388)
                4. Change the coil

                Comment


                  #28
                  Re: Asus X555L backlight shuts off when on battery

                  Just an hour ago had another Asus with the same problem. Replaced coil, got it working.

                  Maybe it is just underdimensioned thus running on its limit and will start acting up after a few years of use.

                  Comment


                    #29
                    Re: Asus X555L backlight shuts off when on battery

                    Originally posted by The_Boss View Post
                    Just an hour ago had another Asus with the same problem. Replaced coil, got it working.

                    Maybe it is just underdimensioned thus running on its limit and will start acting up after a few years of use.
                    Is it a 10 uH coil? You take then from a donor PCBs or do you buy them?

                    Comment


                      #30
                      Re: Asus X555L backlight shuts off when on battery

                      Since I have a pile of scrap donor displays, I get them from there.

                      Yes, marking 100 = 10uH.

                      Comment


                        #31
                        Re: Asus X555L backlight shuts off when on battery

                        Originally posted by The_Boss View Post
                        Just an hour ago had another Asus with the same problem. Replaced coil, got it working.
                        So was your problem similar to mine where there's backlight on AC power only ? Wish I had known of this trick at that time too
                        Wattevah...

                        Comment


                          #32
                          Re: Asus X555L backlight shuts off when on battery

                          Yes, exactly the same problem. Seems to be a problem with Innolux panels.

                          Comment


                            #33
                            Re: Asus X555L backlight shuts off when on battery

                            Sorry for the late reply. Given that the coil which causes the backlight to shut off when the laptop is running on battery is on the panel itself, it means the problem could also be solved with a new panel entirely, can't it ?

                            I can understand why nobody would bother to check with a replacement panel, because they'd plug the adapter in, see the picture come on screen nice and crystal clear and think "nope - display must be fine", but it isn't !

                            Is the backlight driver for these displays located on the panel itself ? I know Louis Rossmann talks about backlight circuits a lot and they're always on the laptop's board and not in the panel itself. It means the LVDS cable carries "B+" to the display which is then stepped up to drive the LEDs...I was curious what sort of voltage one might expect to see on the LVDS connector itself. On Macbooks, the LED voltage itself is present there, which is pretty high.....and dangerously close to the signal lines for the display
                            Wattevah...

                            Comment


                              #34
                              Re: Asus X555L backlight shuts off when on battery

                              A new compatible panel does solves the problem in asus but why replace it if a simple coil replacement solves the problem. The backlit driver is located on the panel itself just near the backlit connector on the screen.

                              Comment


                                #35
                                Re: Asus X555L backlight shuts off when on battery

                                Originally posted by Dannyx View Post
                                has stopped working
                                That's the dumbed-down Windows error message, since Vista, meaning it has crashed with an invalid page fault (called an access violation) or another application-related exception detected by Windows.
                                Last edited by RJARRRPCGP; 11-14-2019, 03:53 PM.
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                                  #36
                                  Re: Asus X555L backlight shuts off when on battery

                                  I had no idea what you were referring to, since you didn't include my full quote, so I looked back and found out I was talking about OpenBoardView not working for me Since then, I actually found a different one called OpenBoardViewER and that works perfectly No idea where it came from TBH, but who cares as long as it does its job.
                                  Wattevah...

                                  Comment


                                    #37
                                    Re: Asus X555L backlight shuts off when on battery

                                    Originally posted by Dannyx View Post
                                    I had no idea what you were referring to, since you didn't include my full quote, so I looked back and found out I was talking about OpenBoardView not working for me
                                    I quoted the "X has stopped working" Windows pop-up.
                                    ASRock B550 PG Velocita

                                    Ryzen 9 "Vermeer" 5900X

                                    16 GB AData XPG Spectrix D41

                                    Sapphire Nitro+ Radeon RX 6750 XT

                                    eVGA Supernova G3 750W

                                    Western Digital Black SN850 1TB NVMe SSD

                                    Alienware AW3423DWF OLED




                                    "¡Me encanta "Me Encanta o Enlistarlo con Hilary Farr!" -Mí mismo

                                    "There's nothing more unattractive than a chick smoking a cigarette" -Topcat

                                    "Today's lesson in pissivity comes in the form of a ziplock baggie full of GPU extension brackets & hardware that for the last ~3 years have been on my bench, always in my way, getting moved around constantly....and yesterday I found myself in need of them....and the bastards are now nowhere to be found! Motherfracker!!" -Topcat

                                    "did I see a chair fly? I think I did! Time for popcorn!" -ratdude747

                                    Comment


                                      #38
                                      Re: Asus X555L backlight shuts off when on battery

                                      Yeah, it's been a while and I forgot WHAT was not working
                                      Wattevah...

                                      Comment


                                        #39
                                        Re: Asus X555L backlight shuts off when on battery

                                        Hello guys. I also have this problem with Asus TP550LD. I would like to order that coil from TME, but I need some small help. I don`t know about curent of the coils. Any guys with TP550LD can confirm about fix with replace the coil in nearing CM509A ?

                                        Comment


                                          #40
                                          Re: Asus X555L backlight shuts off when on battery

                                          Originally posted by mellbo View Post
                                          CM509A ?
                                          Is this a capacitor on the LVDS board of the panel ? Just curious...I don't have a panel on hand unfortunately...
                                          Wattevah...

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