820-00840 wont boot to USB OSX

[ALB-Repairs]

Hi, I have an 820-00840 that had liquid damage around the USB C port

It works perfectly, other than it wont boot to a USB OSX instal. It loads most of the way and then shows the prohibited icon. I have tried many drives, OSX versions and USB C adapters.

It can boot to its internal SSD, and an USB OSX installer, and complete an installation without issue.
I am worried that it not booting to a USB OSX is a symptom of a bigger issue with the board, it seems confusing that we are getting the prohibited icon on this unit, as i have worked on many 820-00840's that boot to a USB OSX without problem.

I have replaced J3300
U2800
Both CD3215's
Reprogrammed EFI with clean ME Region.
Everything else on the unit works, and it works perfectly from the internal SSD

 

[2informaticos]

Does the same on both USB ports?

 

[2informaticos]

If complete USB installation, seems to have good USB communication.
But USB-C ports have lot of lines, apart of data transfer.
Try to compare in diode mode with a known good board.
May be different model, but same configuration.
Also try disconnecting various perypherals.
Test the board with minimum devices possible...