How to measure the LCD connector for backgroundlight? LG G7 Thinq

Hello

I have recently dropped my LG G7 Thinq in a shallow lake, and the phone got waterdamaged. I did try to dry it out but when it asked me to be charged i think i tosted the display. It went black, without a lifesign on it. I found about <2 drops of water in it and i think it came trough the simcard slot. No water what i can recall downwards near the LCD connector.

I ordered a new LCD/digitizer/frame on ebay, and replaced it succefully some days ago. Now the phone is working, but the background light isnt. Also the volume up isnt working yet. But trough vysor everything works as normal.

I have tried to clean off some minor dirt from the motherboard so now it looks good and fine. I will do it even better with IPA and a microscope in my office soon.

But now. the main question is. Is the mothermoard toasted, or did i buy a faulty screen from ebay? I want to measure it and find out, but i have no knowledge in where to measure, and for what. It is a bit annoying that everything works fine except this.

If im not mistaken the LCD connector has 54 main pins + probably 2 on each side.

Can i measure the motherboard some other way, that would also be nice to know about. All feedback is appreciated!