820-00687 NO BACKLIGHT

[2click]

Hi, this board is not creating the EDP_BKLT_EN signal required to enable the backlight chip U8401, is there a way to make a jumper or something so the backlight work again? I know the signal comes from the CPU is there anything that can be done to fix it?
I´ve already tried the monitor with another logic and everything works fine

 

[2informaticos]

Do you get image?
Did you check for external video, or USB activity at least?

Check presence of 3V3/5V_S0SW_LCD and DP_INT_HPD (LCD connected).

 

[2click]

I get image when I connect it to a external display... The computer works fine... it´s just the backlight that isn´t working...
pp3v3_s0sw_lcd = 0 (pulsed to .800)
pp5v_sosw_lcd = 0v (pulses to 5v and drops)

 

[2informaticos]

"and DP_INT_HPD"
Any pulse there?

Check if 3V3/5V_S0SW_LCD, stay high few seconds more without LCD connected.
Also check diode mode to ground on both rails, w/ and w/o LCD assembly.

 

[2click]

DP_INT_HPD = 0 (pulses to ,600 drops to ,250 then to 0v)

diode mode LCD connected
pp5v_s0sw_lcd = ,406
pp3v3_s0sw_lcd = ,453

diode mode LCD disconnected
pp5v_s0sw_lcd = ,570
pp3v3_s0sw_lcd = ,668
DP_INT_HPD = ,781

EDP_PANEL_PWR = 0 (pulses to 3.3 and drops)

 

[2informaticos]

In this case, internal image is also missing.

EDP_PANEL_PWR drops fast too?
Check if stays present few seconds more without LCD.
Did you try another LCD assembly?

 

[2click]

LCD is good, I connected another working logic board to it and it worked fine... EDP_PANEL_PWR drops at the same time that the lcd voltages

 

[2informaticos]

These voltages must be present few seconds at least; even without LCD connected.
Check 3V3/5V_S0SW_LCD behavior on the working board, disconnecting LCD assembly.
Also compare diode mode readings on video lines between the boards.

 

[2click]

I don´t have the working board anymore so I can´t compare the voltages
Is there a way to make a jumper to the enable of U8401 ?

 

[2informaticos]

U8401 requires more than enable signal.
There is an I2C communication with T-CON, inside LCD assemnly.

 

[2click]

So for sure that is working, because it worked with the other board... is the EDP_BKLT_EN a signal or an enable voltage?

 

[2informaticos]

Is a DC signal, which goes high to enable backlight.

However, if DP_INT_HPD is not high, don't waste time with backlight circuit; image is also missing.
PCH needs this signal to detect internal LCD!!!

 

[2click]

ok, thanks anyway!