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Re: macbook pro 820-00840 have image no backlight
This is not correct. Please check again.voltage after fuse 13V
voltage before current sense resistor 5V
If still the same measurement then remove all power.
Check the resistance between the fuse and the current sense resistor.
It should be ~ 0 ohms.
There is something incorrect here. The voltage after the fuse must travel into and exit the current sense resistor.
Update..
What are the full markings of the chip you are replacing at u8400 ?Last edited by mon2; 05-09-2022, 03:14 AM.Comment
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Re: macbook pro 820-00840 have image no backlight
sorry my mistake. i measured wrong current sense resistor.
the current sense resistor is R8400 right?
the resistance between the fuse and the current sense resistor is 0.5 ohm
the voltage at the end of current sense resistor is 13V
hereby i attached the U8400 that i took from A1502Attached FilesComment
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Re: macbook pro 820-00840 have image no backlight
Is this a pic of the donor board or the board you are are repairing ?Comment
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Re: macbook pro 820-00840 have image no backlight
U8400 i took from 820-4924-AComment
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Re: macbook pro 820-00840 have image no backlight
Use the boardview file to confirm that no parts are missing around this backlight IC:
https://www.badcaps.net/forum/showthread.php?t=69489
See some blank pads in the pic. Also no solder shorts.
Have not had enough quality time to review the same.Comment
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Re: macbook pro 820-00840 have image no backlight
any suggestions?Comment
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Re: macbook pro 820-00840 have image no backlight
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Hello, good afternoon, I have the same fault in 820-00850-A, I get 12 volts on both sides of the fuse, R8401 is fine, it has 80.6K and R8402 has 63.4K but my voltage is still 12 volts, I also don't have EDP_BKLT_EN, The resistance is correct any help i replace U8400 and Q8400 could you help me I'm starting in the world of macbooksComment
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Re: macbook pro 820-00840 have image no backlight
Hello and welcome to the forum.
Does your macbook power up and offer a display? (without the backlight)
Can you see the usual graphics with the aid of a flashlight / cellphone torch light?
There is a lid sensor inside the trackpad. A hall effect switch is used to detect if the lid is open or closed.
You can check the voltage to ground of this lid sensor as a start. If the lid is considered to be open, then the ENABLE state will follow to enable the boost LED circuit @ U8400.Attached FilesComment
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Re: macbook pro 820-00840 have image no backlight
Remove all power. What is the resistance to ground of EDP_BKLT_EN?Comment
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Re: macbook pro 820-00840 have image no backlight
So it is not shorted.
Check the voltage to ground of:
ISNS_LCDBKLT_P
ISNS_LCDBKLT_N
There should be little or no voltage drop across these 2 test points else the boost circuit will be turned OFF due to an excessive current draw.
Confirm the resistance to ground of PPVOUT_S0_LCDBKLT. No power when checking resistance.
If the resistance is not low, continue...
Remove R8442. Solder a wire from R8442 pcb pad # 2 = EN pin on the backlight IC to a 3v3 rail on the logic board.
This is to manually enable the backlight IC with a logic '1'. This bypass should then provide for a voltage divider to lower the gate voltage @ Q8400 mosfet to allow for the 12V to enter the boost circuit.
Does this enable the backlight for your board?Comment
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Re: macbook pro 820-00840 have image no backlight
See attached.Attached FilesComment
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Re: macbook pro 820-00840 have image no backlight
After you applied this bypass enable, what is the voltage to ground of PPVOUT_S0_LCDBKLT?Comment
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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... -
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.... -
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 -
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.
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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...
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