820-01598 A2159 board missing Wifi and Bluetooth

[sekidata]

This board came in without liquid damage, but with a missing screen backlight and non-sensitive Touch Bar. I found two burnt & melted inductors (L5100 and L8504) and a burnt via near U8500. Fixing those issues restored the backlight and Touch Bar.

But the board is missing Wifi and Bluetooth (no hardware recognized). It also does not read external USB drives. It does have PP3V3_G3S_WLANBT and PP1V8_G3S_WLANBT.

 

[2informaticos]

Something more affected by liquid.

Do you get 5V at USB devices connected?

You should check all resistors from page 32.
Maybe corroded trace too.
Also try reballing U3701.

 

[sekidata]

Again, no liquid damage on this board.
Yes, I get USB power on external devices. USB drives are also recognized when I start up with the option key pressed.
Resistors around U3701 look good.
Are you suggesting removing the underfilled U3701 and reballing it?

 

[2informaticos]

For USB, you may have problems with U2800; try changing it.

You may need to change U3701 too; should replace the Wifi/TBT ROMS from same donor board.
Try reballing it first.

 

[sekidata]

What's your theory of what happened here? How can overcurrent events on PP5V_G3S_DFR_FILT and PP5V_G3S_DFR_FILT cause damage to the Wifi and the USB-C Data chip? Mysterious. I think it's more likely that something else got damaged (CPU? T2?).