820-01521-A WORKS ON EXTERNAL DISPLAY ONLY

[huzeafa]

Good day guys, have got this board that displays fine on an external display but a black screen on its the internal screen. unit is not liquid damaged, below are some of the screen connector measurements


EDP_PANEL_PWR_BUF_EN =3.2V

DP_INT_HPD= 3.2V

I2C_TCON_SDA_CONN=3.2V

PP3V3_S0SW_LCD= 3V

PP5V_S0SW_LCD =5V

LID_CTRL_DMIC=1.8V

IPD_LID_OPEN= 1.8V

LID_OPEN_LEFT= 1.5V

LID_OPEN_RIGHT=1.5V

SMC_LID_LEFT=1.5V

SMC_LID_RIGHT=1.5V

Please where else do i need to look at

 

[2informaticos]

Don't bother with lid signals, once you get LCD power rails.
This is not possible if lid signals are bad.

Any history available?
Isn't covered by Apple flexgate issue program?

Check voltage and diode mode at L8420; w/ and w/o screen connected.
BKLT_EN_R stays high?

 

[huzeafa]

BKLT_EN_R IS 0V

 

[huzeafa]

Also forgot to mention that am using a fully functional screen, works on a different board.

L8420 stays at 0.032V
DIODE MODE WITHOUT SCREEN 1.272
DIODE MODE WITH SCREEN 1.270

 

[2informaticos]

Do you get image on internal LCD?
Could be dificil to confirm it w/o backlight, but try.

PP3V3/5V_S0SW_LCD present?
Post DP_INT_HPD level.

 

[huzeafa]

PP3V3/5V_S0SW_LCD voltages are present
DP_INT_HPD =3.3V

And I am unable to spot any presence of image

 

[2informaticos]

At least LCD is detected, but image should appear before backlight.

Try changing the small LCD flex cable.

 

[huzeafa]

I HAVE BUT NO CHANGES

 

[2informaticos]

EDP_BKLT_EN comes out from PCH.
Not a good sign.

Try PRAM reset, just in case.