820-00281 no backlight

[Roshon]

This maybe a liquid damaged board works fine with external monitor. but with the internal display i see image but no back light unfortunately i don't nave a test screen or another board to test on U8400
pin1 and 2 LCDBKLT_SW= .1V
PIN 5 PP5V_SO_BKLT_D =5V
PIN 9 ISNS_LCDBKLT_N=12V
PIN 10 ISNS_LCDBKLT_P=12
PIN 11 BKLT_SD=12
PIN 12 BKLT_PWM_KEYB=0
PIN15 BKLT_SCL=4.5
PIN 16 BKLT_SDA=4.5
PIN 17 BKLT_EN_R=3.3
PIN18 PP5V_SO_BKLT_A=5V
PIN 19 BKLT_SENSE_OUT=0
PIN 21 LCDBKLT_FB=0

 

[2informaticos]

Backlight is controlled via PCH -> T-CON -> U8400.
Correct I2C communication is required between U8400 and LCD assembly.

Post diode mode to ground at both pins of D8410; w/ and w/o LCD connected.

 

[Roshon]

At D8410 pin 1 ppvin_sw_lcdbklt_sw with LCD connected is .780
pin 2 ppvout_so_lcdbklt with LCD is .003
I get the same readings with the LCD not connected

 

[2informaticos]

So you have a short inside the motherboard; not caused by LCD assembly.
Is a basic stept to check that, don't miss it in the future.

If LCD connector looks good, then should be a bad capacitor.
Any of C8460-73 can be the culprit; small chance for C8500...

 

[Roshon]

THANKYOU I took every cap off till I found the one that was short it was one of the big 1206 C8467