820-00850 no image after changing u3200

[laptopcity]

Hi i have a water damaged 820-00850 that came in with back right usb not working but everthing else ok , it had water damage around u3200 so changed it and now usb working , i did knock off L3200 next to it but put it back on, before i started i did have a display and now i dont :-( , i have display on external monitor , i did notice some corrosion around u8400 with pin 9 looking bad, guess my question is where to start troubleshooting no image on one of these, do i need screen connected or not ?

 

[2informaticos]

When you diagnose internal image problems, LCD must be always connected.
The internal eDP output is not enabled, if PCH doesn't recognize the LCD.
Resolder U8400 and rebuild traces, if needed.

 

[laptopcity]

Hi finally got hold of some u8400 chips, changed it but also r8445 blown , now have an image , many thanks