A1990 no backlight no image 55V on backlight

[adrko]

Hey guys

Sorry but I have to ask for help, I’m stuck.

A1990 01041 liquid damage
55V on backlight - PPVOUT_S0_LCDBKLT

I have image and backlight on a screen from A2141.

Two known working A1990 screens give no backlight and no image with 55V on backlight

Touchbar works, keyboard backlight works, I can regulate lcd and kb backlight using external screen.

Replaced blown mux chip.
Replaced connector on the screen side tcon board, reconstructed exploded PP5V_S0_ALSCAM_F - L8504, C8504, C8552.

No visible damage anywhere else, logic board aide connector looks fine.

From what I under this might have something to do with led load circuits or backlight sense or even backlight controller U8400.

I’m having trouble understanding how the backlight sense circuit works and how to diagnose it.

 

[adrko]

Solved:
I used and original cable from A1706, will order proper lvds cables.
3$ cables from China aren’t very reliable after all, who could have known {facepalm}

 

[2informaticos]

Keep in mind, when you get higher voltage than normal on backlight output, the electronic circuitry is good.
There can only be open connection to LEDs strip; like bad LCD connector, flex, or screen itself.

 

[adrko]

Aight, thanks. It was unexpected for me that those trouble could be caused by wrong cable. But of course the pin outs vary from one model to another, what can be data pin on one can be ground or unconnected on another