820-00875-01 Spill no screen

U8400 pin 17 has no voltage. The cap connected to it C8442 is gone. What is sending BKLT_EN_R signal and what voltage should it be ? Is it Q9908 ?


Staff member
That's not good.
I supposed you've got 0V there before.
Do you get image on internal screen?

USB activity at least, external video?
I've put it back together, everything works except the backlight - keyboard, trackpad, screen, system boots if I light external light to it I can log in etc.

Seems like U8400 is not being told to turn on the backlight and not drawing down the voltage on R8400 - Q8400 [3] ?
Maybe the enable signal should be debugged somehow ? I don't know how. From other posts I could see there should be 3,3V on U8400[17] - I have 0 there.
Traces look, fine, I have connection from U8400[11] to R8402[2]. R8402 is the one I had to solder on a broken pad, but I checked and it has connectivity both ways and it's not touching GND anywhere. Seems like 12V goes from F8400 > R8400 > R8401 > R8402 > U8400[11] but it's not switched to GND in U8400.

TP[1]PP5V_S0_BKLT_A - 5V



Staff member
No voltage on both sides of R8442?
Check if the first few seconds, when machine chimes.

Try known good compatible LCD assembly.
Last edited:
yes, both sides R8442 0V

"Check ib the first few seconds" - don't understand that.

Only LCD assembly is what I have from the original computer.