Chosen Solution
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 Tomáš
@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.
