macbook pro 820-00840 have image no backlight

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • mon2
    Badcaps Legend
    • Dec 2019
    • 14023
    • Canada

    #41
    Re: macbook pro 820-00840 have image no backlight

    Remove the LCD display and check again.

    Specifically, what is the voltage to ground of the gate pin on Q8400 ? This is a P-channel mosfet so the gate voltage must be lower than the voltage being passed between the source / drain pins.

    With sufficient voltage drop on the gate pin, you should see a non-zero voltage @ PPVOUT_S0_LCDBKLT.

    If necessary, apply a direct ground wire onto the gate pin of Q8400. This will force enable the mosfet and then measure the voltage to ground of PPVOUT_S0_LCDBKLT.

    Also, check the voltage to ground of the following points of interest:

    BKLT_SCL
    BKLT_SDA

    Comment

    • Sacred0489
      Member
      • Sep 2022
      • 21
      • Spain

      #42
      Re: macbook pro 820-00840 have image no backlight

      Originally posted by mon2
      Remove the LCD display and check again.

      Specifically, what is the voltage to ground of the gate pin on Q8400 ? This is a P-channel mosfet so the gate voltage must be lower than the voltage being passed between the source / drain pins.

      With sufficient voltage drop on the gate pin, you should see a non-zero voltage @ PPVOUT_S0_LCDBKLT.

      If necessary, apply a direct ground wire onto the gate pin of Q8400. This will force enable the mosfet and then measure the voltage to ground of PPVOUT_S0_LCDBKLT.

      Also, check the voltage to ground of the following points of interest:

      BKLT_SCL
      BKLT_SDA
      BKLT_SCL 5.1 volt
      BKLT_SDA 5.1 volt
      so now i going to test with the cable to ground to see what i get
      The voltage in gate LCDBKLT_EN_L is 12.60 but when i power on the mac droop to 11.46volt but PPVOUT_S0_LCDBKLT is still 0 volt
      Last edited by Sacred0489; 03-30-2023, 10:06 AM.

      Comment

      • mon2
        Badcaps Legend
        • Dec 2019
        • 14023
        • Canada

        #43
        Re: macbook pro 820-00840 have image no backlight

        The gate pin on the backlight mosfet must be much lower to enable.

        You will need to attach a wire from the gate pin to ground so that effectively you will have 0 volts on the gate. Then measure the PPVOUT_S0_LCDBKLT voltage to ground again.

        While gate is a LOWER voltage (by a few volts or more than what is on the source / drain pins), this P-channel mosfet is enabled.

        The SCL / SDA voltages are a good reading and this means that they are not stuck.

        Comment

        • Sacred0489
          Member
          • Sep 2022
          • 21
          • Spain

          #44
          Re: macbook pro 820-00840 have image no backlight

          Originally posted by mon2
          The gate pin on the backlight mosfet must be much lower to enable.

          You will need to attach a wire from the gate pin to ground so that effectively you will have 0 volts on the gate. Then measure the PPVOUT_S0_LCDBKLT voltage to ground again.

          While gate is a LOWER voltage (by a few volts or more than what is on the source / drain pins), this P-channel mosfet is enabled.

          The SCL / SDA voltages are a good reading and this means that they are not stuck.
          Good morning and sorry for the delay.
          i Connect the gate pin to ground and in PPVOUT_S0_LCDBKLT i have 12v now .

          Comment

          • mon2
            Badcaps Legend
            • Dec 2019
            • 14023
            • Canada

            #45
            Re: macbook pro 820-00840 have image no backlight

            Good. This confirms the mosfet is not defective.

            Lift up one leg of the diode at the output side of the boost circuit. Then with no power, meter in diode mode, check the diode with your meter.

            One probe on one pin. Other probe on other pin.

            What is the measurement?

            Then swap the meter probes.

            Post each measurement.

            Comment

            • Sacred0489
              Member
              • Sep 2022
              • 21
              • Spain

              #46
              Re: macbook pro 820-00840 have image no backlight

              Originally posted by mon2
              Good. This confirms the mosfet is not defective.

              Lift up one leg of the diode at the output side of the boost circuit. Then with no power, meter in diode mode, check the diode with your meter.

              One probe on one pin. Other probe on other pin.

              What is the measurement?

              Then swap the meter probes.

              Post each measurement.
              Hello Thanks for replay and help me so i test the diode and one side gave me 0.333 and the other side gave me OL reversing the tips clearly and with pin 2 (output pin) disconnected

              Comment

              • mon2
                Badcaps Legend
                • Dec 2019
                • 14023
                • Canada

                #47
                Re: macbook pro 820-00840 have image no backlight

                The diode has tested fine and is not the fault. It can be soldered back.

                Is the display now connected?

                What are the voltage readings to ground of the backlight led pins on the display connector? (With the LCD connected)

                Measure carefully since power is on.

                Comment

                • Sacred0489
                  Member
                  • Sep 2022
                  • 21
                  • Spain

                  #48
                  Re: macbook pro 820-00840 have image no backlight

                  Originally posted by mon2
                  The diode has tested fine and is not the fault. It can be soldered back.

                  Is the display now connected?

                  What are the voltage readings to ground of the backlight led pins on the display connector? (With the LCD connected)

                  Measure carefully since power is on.
                  I keep leaving the ground wire of the Q8400 gate to force it to work?? and I connect the display and check the voltage output in the display connection?

                  Comment

                  • mon2
                    Badcaps Legend
                    • Dec 2019
                    • 14023
                    • Canada

                    #49
                    Re: macbook pro 820-00840 have image no backlight

                    Yes. We want to check the LED voltage with your manual feed of the 12v.

                    Comment

                    • Sacred0489
                      Member
                      • Sep 2022
                      • 21
                      • Spain

                      #50
                      Re: macbook pro 820-00840 have image no backlight

                      Originally posted by mon2
                      Yes. We want to check the LED voltage with your manual feed of the 12v.
                      Excuse me, I have tested the voltages in the test points that are below the connector. I think that this is what you were referring to and I only get 5 volts. i attach a pictures with the connector and 11 volt
                      Attached Files
                      Last edited by Sacred0489; 03-31-2023, 07:47 AM.

                      Comment

                      • mon2
                        Badcaps Legend
                        • Dec 2019
                        • 14023
                        • Canada

                        #51
                        Re: macbook pro 820-00840 have image no backlight

                        Will check the schematics once at the office.

                        Test the test pads in the picture you posted.

                        BSCL, BSDA, etc. Check their voltage to ground.

                        Comment

                        • Sacred0489
                          Member
                          • Sep 2022
                          • 21
                          • Spain

                          #52
                          Re: macbook pro 820-00840 have image no backlight

                          Originally posted by mon2
                          Will check the schematics once at the office.

                          Test the test pads in the picture you posted.

                          BSCL, BSDA, etc. Check their voltage to ground.
                          OK thank so much the repair shop are close the weekend so i see you at monday thank a lot for the help

                          Comment

                          • Sacred0489
                            Member
                            • Sep 2022
                            • 21
                            • Spain

                            #53
                            Re: macbook pro 820-00840 have image no backlight

                            So i have a time to take meditions and in this two test point i have
                            BSCL - 5v
                            BSDA - 5v
                            Last edited by Sacred0489; 03-31-2023, 09:44 AM.

                            Comment

                            • mon2
                              Badcaps Legend
                              • Dec 2019
                              • 14023
                              • Canada

                              #54
                              Re: macbook pro 820-00840 have image no backlight

                              Ok. Continue to test the other test points that end with SCL and SDA.

                              Comment

                              • Sacred0489
                                Member
                                • Sep 2022
                                • 21
                                • Spain

                                #55
                                Re: macbook pro 820-00840 have image no backlight

                                Originally posted by mon2
                                Ok. Continue to test the other test points that end with SCL and SDA.
                                Good morning and sorry for the time off i am on holidays, this morning and detect a missing component but i cant find on any schematic o buit map i Attach the pictures.

                                I think maybe this is the cause for the not backlight
                                Attached Files

                                Comment

                                • mon2
                                  Badcaps Legend
                                  • Dec 2019
                                  • 14023
                                  • Canada

                                  #56
                                  Re: macbook pro 820-00840 have image no backlight

                                  Attached.

                                  Remove all power. Meter in DIODE mode. Short your meter probes. Meter should tone beep.

                                  Connect one meter probe to any of the large caps shown with the arrowhead. These caps are mated with the PPVOUT_S0_LCDBKLT backlight rail.

                                  Other meter probe to pin #43 of the LCD connector @ J8500.

                                  Do you hear a tone beep? If not, that trace with the missing part is broken and needs to be fixed.

                                  Suggest to scrap a bit of black solder mask with a sharp knife to confirm that the large trace around the fan opening in the PCB is truly the same PCB trace leading to pin #43 of the LCD connector. Fairly confident that it is.

                                  Excellent find and observation of this PCB layout!!
                                  Attached Files
                                  Last edited by mon2; 04-10-2023, 06:04 AM.

                                  Comment

                                  • Sacred0489
                                    Member
                                    • Sep 2022
                                    • 21
                                    • Spain

                                    #57
                                    Re: macbook pro 820-00840 have image no backlight

                                    Originally posted by mon2
                                    Attached.
                                    thanks for the picture in the schematic i get do not have the type of component that is why it is seen in the photo, it is a resistor, could you tell me what its values are, thanks

                                    Comment

                                    • mon2
                                      Badcaps Legend
                                      • Dec 2019
                                      • 14023
                                      • Canada

                                      #58
                                      Re: macbook pro 820-00840 have image no backlight

                                      Just updated my last post -see above.

                                      Comment

                                      • Sacred0489
                                        Member
                                        • Sep 2022
                                        • 21
                                        • Spain

                                        #59
                                        Re: macbook pro 820-00840 have image no backlight

                                        Originally posted by mon2
                                        Attached.

                                        Remove all power. Meter in DIODE mode. Short your meter probes. Meter should tone beep.

                                        Connect one meter probe to any of the large caps shown with the arrowhead. These caps are mated with the PPVOUT_S0_LCDBKLT backlight rail.

                                        Other meter probe to pin #43 of the LCD connector @ J8500.

                                        Do you hear a tone beep? If not, that trace with the missing part is broken and needs to be fixed.

                                        Suggest to scrap a bit of black solder mask with a sharp knife to confirm that the large trace around the fan opening in the PCB is truly the same PCB trace leading to pin #43 of the LCD connector. Fairly confident that it is.

                                        Excellent find and observation of this PCB layout!!
                                        from the cap to pin 43 there was no continuity so we scraped away the solder mask and tested the continuity to pin 43 and it had continuity , so i need to know find the value of the resister to replace it .

                                        Comment

                                        • mon2
                                          Badcaps Legend
                                          • Dec 2019
                                          • 14023
                                          • Canada

                                          #60
                                          Re: macbook pro 820-00840 have image no backlight

                                          The schematic does not show this missing part.

                                          From the picture of the boardscan from a paid database, this appears to be a ferrite bead. It is not technically required for the operation so you can just short the pads to allow for the backlight to reach the LCD display.

                                          For initial testing, it is recommended to bridge the pads.

                                          Otherwise, this part looks like an 0603 or 0805 ferrite bead (1A or higher should be ok) - we like to use 600 ohms in our designs but 300 ohms should be ok.

                                          We use the parts from MaxEcho (Taiwan) but many others on the market are also ok to consider if you wish to apply this part.

                                          http://www.maxecho.com.tw/en/product...d__ACMS_series

                                          If possible, review the physical pad sizes on the pcb. Or as a plan B, take a part that is 0603 from any donor board and see if it fits over the pads you have that are missing this component. If it does not, try 0805 (will be a larger part). Then proceed to seek out a ferrite bead to replace this component.

                                          In summary, this part will clean up / filter noise on the LED backlight voltage.

                                          Comment

                                          Related Topics

                                          Collapse

                                          • Constantinos
                                            Macbook Pro A2442 820-02098 No image but has backlight
                                            by Constantinos
                                            Hi all
                                            I have a Macbook Pro A2442 with the 820-02098 from a friend which has no picture on the display, however, the backlight works.
                                            He was streaming a football match on a questionable site, then the site crashed, and the problem emerged.
                                            Initially, he sent it to apple, who quoted him £1323.95 to replace the display, lid angle sensor and top case.
                                            Obviously, he decided against this and gave it to me so that I could have a crack at it.
                                            From initial diagnostics, I connected to an external monitor, I first tried with a HP 22W monitor, and I booted into the boot menu...
                                            08-24-2024, 09:48 AM
                                          • Roccolade
                                            Macbook Pro 820-01814 no image or backlight
                                            by Roccolade
                                            Hi! I'm a bit new to this whole repair world. But this is what i'm working on:

                                            A Macbook Pro A1990 (820-01814) from 2018. It has no image – or backlight for that matter.

                                            No history of liquid spills or anything. It's fully functional on external monitor - and the webcam works.. But it doesn't seem like the internal display is even detected.

                                            Sometimes the backlight lights up, when booting into recovery mode. (No image still)
                                            That's the only progress I've gotten.

                                            I tested the panel on another Macbook, and the display worked perfectly....
                                            03-07-2023, 05:29 AM
                                          • arevut
                                            Macbook Air 2020 13” model: A2337 backlight is on but no image
                                            by arevut
                                            Hi all! MacBook Air A2337. There are no traces of liquid or obvious damage, the motherboard is visually in perfect condition. The image is displayed on the external screen, but only the backlight works on the internal screen. There is no image, and the camera on the built-in screen does not work. How to exclude during diagnostics that it is the screen that is broken and not the motherboard? What signals should be present on the connector with the screen removed and connected?
                                            02-07-2024, 08:07 AM
                                          • Comp_Pro
                                            No Backlight Macbook A1990 820-01041
                                            by Comp_Pro
                                            Hello all,

                                            Am trying to figure out this backlight issue with this A1990 Macbook Pro.

                                            Tests performed:

                                            There is no backlight even with a good screen.
                                            Backlight IC is receiving the correct support voltages.
                                            Fuse F8400 ok
                                            Current sense resistor R8400 ok
                                            Backlight IC is receiving 3.3V on enable pin.
                                            Backlight IC receiving voltage from PPBUS_G3H, aprox 12.5V.
                                            Backlight IC receiving 5V from PP5V_G3S
                                            Backlight IC BKLT_SCL and BKLT_SDA both measure 0.545V diode mode to ground
                                            I2C_BKLT_SCL and I2C_BKLT_SDA both measure...
                                            05-06-2024, 10:23 PM
                                          • imcool
                                            Macbook Air A1466 no backlight no image
                                            by imcool
                                            Hello,
                                            On this Macbook Air A1466 with 820-00165
                                            I have only 8V on backlight line but no high voltage in boost circuit, I have checked all components like caps and diode and they seems to be ok.

                                            I have noticed that when macbook chimes after turning on there is no image at all even with flash light,

                                            I have tried 2 different OEM LCD and still there is no image,
                                            I see the LCD fades out when i remove power or turn off the macbook.

                                            I have 2 problems
                                            1 No image
                                            2 No backlight, but i have 8VDC on backlight circuit.
                                            ...
                                            12-14-2020, 02:18 PM
                                          • Loading...
                                          • No more items.
                                          Working...