820-00239 No backlight.

[bjf]

This board boots and has display on external monitor. Can't tell if it has video on LCD screen. Has EDP_BKLT_EN at 3.3V. Has PP5V_S0SW_LCD at 5V. 0V on PPVOUT_LCD_BKLT. Is this just a U8400 replacement? I'm trying to rule everything else out before just replacing it. The board was hit by liquid in that area. C3504 was ugly and needed replaced. Other than that it looks pretty good. Diode measurements are coming up normal.

 

[2informaticos]

U8400 is controlled through I2C bus from LCD panel.
Do you note any liquid sign at J8500 area?
Video data lines come out directly from CPU.
Its eDP output could be damaged now...

 

[bjf]

No damage near J8500 or anywhere along the top. The only place the board got his was at the bottom near U8400.

 

[bjf]

So I guess I'll have to try replacing U8400.

External monitor is working. Would that still work if eDP is blown?

 

[2informaticos]

Video outputs are different for internal LCD and external monitor.
iGPU core processes all, but has two separate outputs.

 

[ronaldo]

I came to this post as I had exactly the same issue and symptoms. All EDP line is OK.
The problem was the screen cable had a tiny crack on it just visible on the microscope.