820-2850 No image

[Naevius]

I have a 820-2850 board that doesn't display an image (checked with a flashlight from the back). Backlight also doesn't work.

There was liquid damage on the LCD connector, replaced connector, but still no image. Currently don't have a mini-displayport convertor, so can't check image externally.
Device seems to boot, since I hear the chimes and PPVCORE_S0_CPU is present.

SMC_LID = 3.4V
PPVCORE_S0_CPU = 1.38V

PPVOUT_S0_LCDBKLT is not present (no short), BKLT_EN is also not present. Traced this down to LCD_BKLT_EN which is not present. Since LCD_BKLT_EN comes from U9600, I've reach a dead end here.

So it's not being told to turn on the LCD/backlight, while it is booted and the lid is open. Since I have limited experience with macbook repairs, I'm kind of at a dead end here. Where to look for next?

 

[Naevius]

*Subtle kick*
Anyone has an idea where to look for the issue?

I've ordered a mini-displayport->HDMI convertor, but I have this feeling it's not going to display anything externally also.

 

[Naevius]

I'm not sure if I have a compatible known good working LCD. I have a donor A1278 and A1465 with known good LCD assemblies for example. Any easy way to check compatibility?

Visually the traces coming from J9000 seem fine. I measured those on the same side of the board, and seem fine.

Voltages:
Pin 4 (PP3V3_S0) = 3.27V
Pin 6 (LVDS_DDC_CLK) = 3.26V
Pin 7 (LVDS_DDC_DATA) = 3.26V

Voltages are the same with and without the LCD connected.

R9010/11 are 65k-75k in circuit, so seem fine. L9000/10/11 also seem fine. Coils in L9010/11 are 1.5/2 ohm each, L9000 is 0.5 ohms.

I used the connector to replace from a donor board. Even tho it seems ok even with 40x magnification under the microscope, I've ordered some new connectors just to be 100% sure.

But even without a LCD connected I should be getting (a relatively high) voltage on PPVOUT_S0_LCDBKLT, right? Or should there be a connection with the LCD before U9600 turns it's LCD_BKLT_EN output on?

 

[2informaticos]

If LCD is not properly recognized, forget about activating video, or backlight.
You need compatible LCD...