2.4GHz, 2.7GHz, oder 2.8GHz quad-core Intel Core i7 Prozessor (mit Turbo Boost bis zu 3,8GHz) mit 6MB geteiltem L3 Cache.

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no lcd - no lcd_pwr_en, no backlight - no lcd_bklt_en

Hi @refectio,

yesterday i started working on Macbook Pro 15" 2013 with board number 820-3332-A with no backlight / no display issue.

This motherboard has already been repaired by somebody before. I checked every component and LCD / BKLT line and found missing LCD_PWR_EN and LCD_BKLT_EN. When i inject 3,4V to LCD_BKLT_EN, lcd backlight work but here is no image.

I tried reball U9100 but same problem.

LCD_PWR_EN resistance -> 0.615

LCD_BKLT_EN resistance -> 0.590

My queston is how to test U9100 (MCU???) or have somebody same problem? Thanks for your answer !

Best regards


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Hi Tomas, I would ask the board-level macbook experts to help out here (@reecee @arbaman @tcrs_circuit).


@refectio Hard to describe how much I dislike to have to try to fix a board someone before me has unsuccessfully tried to repair..am I the only one ?

I don't have correct resistance data on those rails. Might be U9100 was fried, is U9000 in good shape or faulty too ? What was the Mac original issue..without any history and a possible random human damage is like shooting in darkness here.


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@honzo I assume you resoldered U8900 before attempting all this, since this is a common fault on early 2013 models? If not, I hope you didn't mess up U9100 by reballing...

Haven't got a schematic in front of me at the moment but I believe U8900 sends a GPU good signal to U9100 which will allow U9100 to produce the required signals for backlight and image. If U8900 is not sending the PGOOD signal to U9100 (which happens due to bad solder joints on the chip), there will be no image or backlight on the screen whatsoever.

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Thanks for answer @reecee and @arbaman . After reading your post i found, that:

GPUVCORE_PGOOD is not present because GPUVCORE_EN is not present, multimeter show me 0V when macbook is power on. Yesterday i lent full working motherboard with same number. Resistance defective board of GPUVCORE_PGOOD and GPUVCORE_EN are same as of full working board , lines are not short to ground.

I tried also inject voltage:

When i connect 3,3V to GPUVCORE_EN, GPUVCORE_PGOOD is present but still no LCD no Backlight.

When i connect 3,3V to LCD_BKLT_EN backlight work.

Any idea where can be problem? I also tried reball U8900 and U9100 but no luck.

Thanks !


GPUVCORE_EN comes from U9100, it could be one of 4 things;

1. U9100 is faulty

2. You have not resoldered U9100 properly, or have damaged it with too much heat

3. One of the previous GPU sequencing rails are missing, which come from U9100 too (but one may be missing for another reason).

4. Bad GPU

Replace U9100 after checking the sequencing rails, if still the same will be the GPU. Just to check too, you have made sure you are using a good screen, and the LCD connector is good (change this first to make sure), since U9100 will not send these signals if screen is not recognised. Make sure it chimes too, otherwise it is not just a picture issue


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Tomas wird auf ewig dankbar sein.
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