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Old 11-25-2022, 06:58 AM   #21
Strolch
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Default Re: Macbook A1990 820-01041-A Dark Display

ok, good that you are here. Thx
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Old 11-27-2022, 07:59 AM   #22
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Default Re: Macbook A1990 820-01041-A Dark Display

Hi mon2,
i have
R8401 12,55Volts
C8401 Pin1= 0,04Volts Pin2= 12,55Volts
Q8400 Pin 3+4= 12,55Volts
R8442 Pin1= 0,0006 Volts
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File Type: jpg Messung.jpg (698.7 KB, 4 views)
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Old 11-27-2022, 08:31 AM   #23
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Default Re: Macbook A1990 820-01041-A Dark Display

With R8442 at 0v, the backlight circuit is not being enabled.

Check the lid switch voltage to ground. This hall effect switch is inside the trackpad and often causes problems. With no power, also confirm that the interface cable contacts are clean and properly seated. IPA and a cotton swab are great to clean the cable contacts. If the logic board believes the lid is closed, the backlight will remain off.
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Old 11-27-2022, 09:10 AM   #24
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Default Re: Macbook A1990 820-01041-A Dark Display

ok, but I took the measurements with the logic board removed. The measuring points are all on the back.
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Old 11-27-2022, 10:54 AM   #25
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Default Re: Macbook A1990 820-01041-A Dark Display

Ok. See attached.

Measure the voltage to ground of the IPD_LID_OPEN signal.
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File Type: png U4802_IPD_LID_OPEN.png (84.0 KB, 3 views)
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Old 11-27-2022, 11:31 AM   #26
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Default Re: Macbook A1990 820-01041-A Dark Display

I have 1,794Volts at Pin 4 U4802. And There are solder balls on the U4802 at pin 4 and pin 3
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Old 11-27-2022, 11:44 AM   #27
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Default Re: Macbook A1990 820-01041-A Dark Display

LID sensor is OK.

What is the voltage to ground of:

I2C_DISP_SCL
I2C_DISP_SDA

PP1V8_S5_GPIOX_R ; power to the MUX (and the (tech) people)
PP3V3_S5_GPIOX_R



The above are used to deal with the display (U9801) and also the backlight enable signal.

PS: Have to check out for a few hours for the usual grocery shopping. Purchased some new security cameras for the business and the NEXT day they dropped the price. Really?? Price adjustment time
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Old 11-27-2022, 12:24 PM   #28
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Default Re: Macbook A1990 820-01041-A Dark Display

Ohh;-)
I2C_DISP_SCL = 1,79Volts
I2C_DISP_SDA = 1,79Volts
PP1V8_S5_GPIOX_R = 1,79Volts
PP3V3_S5_GPIOX_R = 3,34Volts
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Old 11-27-2022, 07:21 PM   #29
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Default Re: Macbook A1990 820-01041-A Dark Display

With no power to the board, meter in resistance mode, check the resistance across R8401.

It should be ~80k ohms.

Last edited by mon2; 11-27-2022 at 07:24 PM..
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Old 11-28-2022, 03:57 AM   #30
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Default Re: Macbook A1990 820-01041-A Dark Display

yes 80,42k
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Old 11-28-2022, 02:48 PM   #31
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Default Re: Macbook A1990 820-01041-A Dark Display

What else can I do? Another idea? br
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Old 11-29-2022, 06:09 AM   #32
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Default Re: Macbook A1990 820-01041-A Dark Display

Does this display function on another logic board?

The logic board works with an external monitor?

This model is impacted by flexgate so the fault may be broken interface cabling on the display assembly.

https://youtu.be/k0xZe_4D8C0
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Old 11-29-2022, 03:53 PM   #33
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Default Re: Macbook A1990 820-01041-A Dark Display

Yes, everything is ok on the external monitor! I just bought a same A1990 with defective board. Since the display is intact. I'll put my board there!
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Old 11-29-2022, 03:56 PM   #34
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Default Re: Macbook A1990 820-01041-A Dark Display

No Flexgate, then I rather think that the board got some liquid from the display. It's also getting very warm, I just noticed.
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Old 11-29-2022, 06:26 PM   #35
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Default Re: Macbook A1990 820-01041-A Dark Display

Hi, its the Display!! I found another A1990 here! and the display is intact. It works! So the board is defective from the display! Can you also buy the board?
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Old 11-29-2022, 07:27 PM   #36
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Default Re: Macbook A1990 820-01041-A Dark Display

That is good news ☺️

For knowledge, watch this video where only the lcd is replaced for a macbook. This is a lower cost option but then is a longer servicing time for the procedure.

https://youtu.be/I_kcMyhwZls

Do read the comments as well. Personally is on my things to do list but first need to fix up our company and take legal action against the guilty one. Lawyer meetings this week.
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Old 11-29-2022, 07:37 PM   #37
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Default Re: Macbook A1990 820-01041-A Dark Display

Can I also buy the display board? Then you don't have to replace the display if only the board is defective!
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Old 11-30-2022, 06:52 AM   #38
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Default Re: Macbook A1990 820-01041-A Dark Display

Have not seen only tcon board repair but ask the lcd vendors on AliExpress.
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