Need help 820-00923 no backlight Newbie here

[alontest]

Hello there, newbie here

Have a MacBook pro to repair with no backlight. Thought that it was a faulty screen, so tested with good known working screen but still no backlight. There are no liquid signs at all on the board, the board looks clean as new.

So started tracing all power rails and spot that PPVIN_S0SW_LCDBKLT was missing after Q8400 so found and replaced faulty capacitor C8473 and that fixed this rail but still have no backlight.

Started investigating further and spot that U8400 LCDBKLT_FET_DRV is 0V and it can't open Q8401. So is it a U8400 faulty or the issue could be somewhere else ?

These are the readings from U8400:
LCDBKLT_SW - 0.12V
GND_BKLT_SGND - 0V
LCDBKLT_FET_DRV - 0V
PP5V_S0_BKLT_D - 5.13V
ISNS_LCDBKLT_N - 13.03V
ISNS_LCDBKLT_P - 13.03V
BKLT_SD - 9.32V
BKLT_PWM_KEYB - 0v
BKLT_SCL - 4.61V
BKLT_SDA - 4.52V
BKLT_EN_R - 3.34V
PP5V_S0_BKLT_A - 5.13V
BKLT_SENSE_OUT - 0V
LCDBKLT_FB - 11.19V
GND_BKLT_SGND - 0V

Any suggestions would be more than welcome.

P.S. The MacBook starts and works perfectly just no backlight, I can see Apple logo and so on.

[MobileXT]

Re: Need help 820-00923 no backlight Newbie here

Did you check for shorted on the backlight power rail?

[alontest]

Re: Need help 820-00923 no backlight Newbie here

Fixed it, the problem was faulty Q8400