A1932 - no image , no backlight

[JamesGecko]

LCD EDP connector has been changed.
i 've checked on 3 LCD A1932 -> same result.
Hdmi is working.

Here are the measurements I took on the LCD / backlight section, without LCD connected
PP5V_S0SW_LCD = 5 V
PP3V3_S0SW_LCD = 3.3 V
EDP_PANEL_PWR_BUF_EN = 3.3 V

PPVOUT_S0_LCDBKLT = 0 V
PPVOUT_S0_LCDBKLT_F = 0 V
this result is normal without LCD connected ?

Q8400:
PPVIN_S0SW_LCDBKLT = 0 V
PPVIN_S0SW_LCDBKLT_F = 12 V
PPVIN_S0SW_LCDBKLT_R = 12 V

U8400:
BKLT_EN_R = 0 V
VVDD = 5 V
VVDA = 5 V
EDP_BKLT_EN = 0 V (not shorted)
R8451 /R450= 0ohm,
I2C_BKLT_SCL = 4.8V no pulsing
I2C_BKLT_SDA = 4.8V no pulsing

backling is off but power of lcd is ok ,maybe because there is no lcd connected.
if you can share measurment of same logic board , i 'd like to compare.
thanks .

 

[2informaticos]

Any video/backlight voltage checking MUST be done with LCD connected.
PCH expects HPD signal from it, prior to enable eDP output.

 

[JamesGecko]

i connected an screen and same result .
i have forced EDP_BKLT_EN to 5V and PPVOUT_S0_LCDBKLT up to 30-40v
no pulsing on I2C_TCON_SCL_R / SDA( stable to 3.3V)
no pulsing on I2C_DISP_SCL / SDA (stable to 1.8V)

 

[2informaticos]

No reason to force backlight enable signal.
PCH will not send any video signal to LCD assembly if HPD signal stays low.