Macbook Pro A1990 (820-01814) no backlight display

[XVLZ]

Hello world.

I'm newbie here

The problem with my macbook pro 15 2019 (touchbar) is that one day before going to bed I closed the lid, and in the morning I found that the backlight of the display does not work (there is an image, i can see it with a flashlight).

Nothing was ever spilled on the macbook, never dropped, disassembled only once to replace the battery.

My friends and I tried to diagnose the problem on our own, but we didn't come to anything, we replaced the U8400, it didn't succeed, flexgate seems to be normal, although I'm not sure about it.

So I want to ask for your help, let's start all over again and diagnose under your sensitive guidance of knowledgeable and understanding people.

Where should I start? What do I need to measure with the power on? What I need to check, in which multimeter mode and so on. I am quite new to these matters, but there are no specialists in my city who would take up this problem. They only tell me that I need to either replace the display or the motherboard assembly, and this is incredibly expensive.



Thank you so much for reading this thread to the end, I hope for your help

MBP 15 2019 (A1990)
820-01814-A

[mon2]

Re: Macbook Pro A1990 (820-01814) no backlight display

Start with checking the backlight fuse at F8400.

What is the voltage to ground of each side of this fuse?

[XVLZ]

Re: Macbook Pro A1990 (820-01814) no backlight display

Start with checking the backlight fuse at F8400.

What is the voltage to ground of each side of this fuse?

Thanks for the answer, as soon as possible I will try to get to the macbook and make a measurement

[piernov]

Re: Macbook Pro A1990 (820-01814) no backlight display

https://logi.wiki/index.php/Backlight_Troubleshooting

[XVLZ]

Re: Macbook Pro A1990 (820-01814) no backlight display

https://logi.wiki/index.php/Backlight_Troubleshooting

Hello, yes we have already checked these options and I have a brd for the viewerboard
big thanks

[XVLZ]

Re: Macbook Pro A1990 (820-01814) no backlight display

Start with checking the backlight fuse at F8400.

What is the voltage to ground of each side of this fuse?

sorry for the stupid question, but how to measure the voltage of this element if it is on the back of the motherboard?

[XVLZ]

Re: Macbook Pro A1990 (820-01814) no backlight display

Start with checking the backlight fuse at F8400.

What is the voltage to ground of each side of this fuse?

my laptop must be connected to power, then what is the right way to measure it? i need to remove the motherboard to get to the F8400, how can i connect it to power?

[mon2]

Re: Macbook Pro A1990 (820-01814) no backlight display

Review the boardview file. Locate this fuse.

Select one side of the fuse. When you do, the pad on the fuse will turn yellow to highlight the pin. Also the net connection to other parts will also be highlighted. Hoping that you will find a point to measure on the side visible to you. Once at the office, will try to find the same. Will be there in about 2 hours from now.

[XVLZ]

Re: Macbook Pro A1990 (820-01814) no backlight display

Review the boardview file. Locate this fuse.

Select one side of the fuse. When you do, the pad on the fuse will turn yellow to highlight the pin. Also the net connection to other parts will also be highlighted. Hoping that you will find a point to measure on the side visible to you. Once at the office, will try to find the same. Will be there in about 2 hours from now.

I was able to track only 1 pin fuse F8400, because pin 2 does not go to the front side of the motherboard, I attached screenshots

I measured C6405 and C6406 on the highlighted pins, and got 12.88 V in DC mode

[mon2]

Re: Macbook Pro A1990 (820-01814) no backlight display

See attached. These are the points of interest to measure the voltage to ground.

In summary -> fuse has to be present so the source voltage can enter the mosfet above -> if the GATE voltage is LOWER than the voltage passing between SOURCE & DRAIN pins, the mosfet will ENABLE.

This is a P-channel mosfet.

The boost led IC that you see on this page needs to be ENABLED and the communication with the i2C lines (SDA & SCL) must be present and not being pulled down. This device is an I2C slave and there is a I2C master on the main logic board. When this slave is indexed using an I2C address, the dimming can work.

The final boosted voltage is at the output of the diode on this schematic page.

Do note that the display has to be detected for the backlight to work.

There are many detailed websites and comments from others on the operation of this circuit by @Piernov and others but the above is a short summary.

I am flooded with some life sucking repairs and dealing with my first PMIC replacement on an ipad AIR - without a microscope - not fun at all. Do not have the hand stability to solder back 01005 parts. Trying to get the repair out to the customer before a major snow storm hits this region.

Post the voltage checks for the requested areas when you can.

Start with the ENABLE pin voltage for the backlight IC = pin 17 of U8400. You can measure this voltage @ R8442 or C8442 (only pads are on the PCB; part is NOT stuffed at the factory).

[XVLZ]

Re: Macbook Pro A1990 (820-01814) no backlight display

See attached. These are the points of interest to measure the voltage to ground.

In summary -> fuse has to be present so the source voltage can enter the mosfet above -> if the GATE voltage is LOWER than the voltage passing between SOURCE & DRAIN pins, the mosfet will ENABLE.

This is a P-channel mosfet.

The boost led IC that you see on this page needs to be ENABLED and the communication with the i2C lines (SDA & SCL) must be present and not being pulled down. This device is an I2C slave and there is a I2C master on the main logic board. When this slave is indexed using an I2C address, the dimming can work.

The final boosted voltage is at the output of the diode on this schematic page.

Do note that the display has to be detected for the backlight to work.

There are many detailed websites and comments from others on the operation of this circuit by @Piernov and others but the above is a short summary.

I am flooded with some life sucking repairs and dealing with my first PMIC replacement on an ipad AIR - without a microscope - not fun at all. Do not have the hand stability to solder back 01005 parts. Trying to get the repair out to the customer before a major snow storm hits this region.

Post the voltage checks for the requested areas when you can.

Start with the ENABLE pin voltage for the backlight IC = pin 17 of U8400. You can measure this voltage @ R8442 or C8442 (only pads are on the PCB; part is NOT stuffed at the factory).

Is it enough for me to connect type c charging cables to the motherboard and display cables so that I can measure these elements?

at the same time, the motherboard can be removed from the case, but connected to the power supply and the display so that I can get to the necessary circuit elements?

[XVLZ]

Re: Macbook Pro A1990 (820-01814) no backlight display

I will try to take measurements tomorrow, so far I have measured only the D8410 because it is on the front side of the motherboard
the measurement results are in the screenshot

[mon2]

Re: Macbook Pro A1990 (820-01814) no backlight display

On this measurement at the diode, be in DC volts (35 volts or higher).

Red probe on diode; black probe to ground.

Review what the voltage is on the diode (both sides should be measured).

If working, you should see a boosted voltage of 25-45 volts after the diode to drive the LED backlight array inside the display.

[XVLZ]

hello mr mon

I measured only the key parts of the circuit highlighted by you, I am attaching a screenshot. It turned out to be not easy in fact, but I built such a structure for measurements, attached

By the way, the multimeter mode used this one, just in case I show it in the attachment

Now I will start measuring the ENTIRE circuit step by step, tell me if anyone has measurements of a working board, each of the elements?



finally I was able to measure a section of the circuit, that's what I got
voltage measurements in attachment

[XVLZ]

Re: Macbook Pro A1990 (820-01814) no backlight display

I'm confused again, can you tell me what the problem might be and where to look?

[mon2]

Re: Macbook Pro A1990 (820-01814) no backlight display

Pin 17 of the backlight = EN = is currently @ 0 volts. So this means the upstream logic is requesting that the backlight remain OFF.

The fault could be that the display is not being detected due to a faulty cable / connector / mating issue of the cable & logic board connector. Remove all power and confirm that the contacts are clean on the display connector. Use IPA to clean the contacts which is always nice to do.

You can also confirm the OPEN LID status which is based on the trackpad and hall effect switches. That is, if the LID is sensed to be OPEN, then the backlight will be enabled.

PS: Need to play toilet repair man for my mother at -20 C temps outside. Fun never ends. BBL8R.

[XVLZ]

Re: Macbook Pro A1990 (820-01814) no backlight display

Pin 17 of the backlight = EN = is currently @ 0 volts. So this means the upstream logic is requesting that the backlight remain OFF.

The fault could be that the display is not being detected due to a faulty cable / connector / mating issue of the cable & logic board connector. Remove all power and confirm that the contacts are clean on the display connector. Use IPA to clean the contacts which is always nice to do.

You can also confirm the OPEN LID status which is based on the trackpad and hall effect switches. That is, if the LID is sensed to be OPEN, then the backlight will be enabled.

PS: Need to play toilet repair man for my mother at -20 C temps outside. Fun never ends. BBL8R.

I am very grateful for your help, I will understand, look for how to diagnose cables, loops and connectors
By the way, I already diagnosed the lid opening sensor through the terminal on the macbook, I use an external monitor for work
lid opening sensor is ok

[XVLZ]

Re: Macbook Pro A1990 (820-01814) no backlight display

so.. i found out the following

J0200
not sure if I'm doing it right. in diode mode, two test points rang (black probe on the ground, red on the test point) when the cable is connected, everything is OK, but if you turn it off, there is discontinuity

also I measured the voltage on these test points, both have 5 V (BLDA, BSCL)

J0803
also in diode mode, the test point VLED on J0803 rang, it has continuity to ground (while J0200 was connected)

however, when measuring voltage at VLED 0 V (while J0200 was connected)

I got lost again , what could be the reason? where to look for damage?

[XVLZ]

Re: Macbook Pro A1990 (820-01814) no backlight display

UPD

I'm sorry, I completely forgot to say that my webcam and key backlight also do not work. maybe this info will help

[mon2]

Re: Macbook Pro A1990 (820-01814) no backlight display

In diode mode testing, the RED lead, yes red meter probe to ground.

Black meter probe to point to test.