Apple Macbook Pro A2485 820-02100 Water Damaged, Power, No display

[ameasere]

820-02100 with water damage, corrosion around U5200 but was cleaned with IPA. Device chimes, touchpad clicks, successfully negotiates from 5V to 19.5V and hovers between 0.006 and 0.4A. It will spike for only a second up to 1A, then immediately drop down to 0.1A - if left long enough, it will get stuck after power cycling once and sitting at 4.94V 0A.

During the first few stages, touchpad clicks and I can hear (quite loudly) "voiceover off" if I press the power button repeatedly. No picture on screen, no fan spin, and nothing over HDMI - though it does wake up the monitor over HDMI, but no picture is ever sent. Sometimes it will ramp up the fans to 100% and stay like that until power cycling, and others I get no fan spin at all.

Under thermal camera, the board is mostly cold. M1 RAM chips get a little warm at 30C, and a 25-30C signature from the shroud covering L5800/20/40 coils.

UN400 has a small black blob which I am unsure of - I understand from Louis Rossmann's prior videos that if this chip blows, it usually sends 12V to the NAND and ruins all chances of data recovery. I hope this is not the case. I have attached a photo of this strange blob.

Same symptoms with battery plugged in and unplugged.

Please do advise on any next steps to further check and diagnose.

Voltages observed

PPBUS_AON - 12.6V
PP3V3_AON - 3.3V
PP3V3_S2 - 3.3V
PP5V_S2_MAIN - 5.1V
PP3V8_AON - 3.8V
PP1V8_AON - 1.8V

 

[2informaticos]

NANDs should be good, if machine boots.

Did you check HDMI video disconnecting internal LCD?

I bet for more corroded components/traces.
Inspect the MLB on both sides under miscroscope.
Pay atention to the connectors.

 

[ameasere]

A combination of your ideas worked! The screen does not work, and I have to open and close the lid a few times for the external monitor to display a picture in clamshell mode. I went over both sides of the board again and cleaned up anything that looked remotely suspicious, and tried HDMI with/without the internal LCD connected. It only worked with the LCD connected, in clamshell mode - screen is still blank sadly. If the client wishes to replace the screen, we may be able to see better results. Getting to the desktop, the laptop now draws the full 2.1A as expected on the meter. Thanks for your help!!