820-02016 A2337 liquid damage weired behaviour

[jadao]

Hello 2informaticos,

This board was liquid damaged, with shorted P5V_PS2 line at U5700, shorted UP710, burned LP670 due to the screen and burned trace related to backlight ic UP800. Even the screen was not powering on because internal lcd IC chip was shorting PP5V_SW_LCD.

I was able to fix all this stuff and make the board boot again with screen, however if I shutdown the laptop it wont start anymore.
If I restart also the laptop it won't start anymore.

I have to unplug the battery, and plug back the magsafe cord to see the laptop starting again.
I ruled out all the basics: battery, kbd/trackpad, audio board but still the same.

I compared with working board the following:

With good board and no battery:
When I shut down the laptop, USBC meter sequence is 20V -> 0V -> 5v -> 20V 70mA
At this stage (powered off) I still have PP5V_S2: 5.2V
PP3V8AON_PH1: 3.8V
Laptop restarts as soon as I click the trackpad, the keyboard or press the power button.

With the bad board and no battery:
When I shut down the laptop, USBC meter sequence is also 20V -> 0V -> 5v -> 20V 70mA
But at this stage I don't have anymore PP5V_S2 (it's 0V)
and PP3V8AON_PH1: is fluctuating 3.0 - 3.2V instead of getting 3.8V
Laptop doesn't restarts if I click the trackpad (there is no force touch enabled), if I press a key on the the keyboard or if I press the power button.

I don't know where I should start looking?

Thanks as always!

 

[2informaticos]

Check the lid signals.
Machine comes back from sleep when close/open the lid?

 

[jadao]

Lid signals (AMR_LEFT_OR_ND_1V8 and AMR_RIGHT_OR_ND_1V8) are ok with 1.54V, it seems a bit off but normal after comparing with other board, machine also comes back normal when lid is opened/closed.

I solved it, finally, it was a mistake on my end...U5700 with pins 27 and 28 bridged underneath the ic. It had the nasty quick chip low melt solder that spread between 2 pads. I used low melt solder in a previous job to desolder a dc jack and apparently I didn't clean the tip properly.

P3V8AON_BST3 and P3V8AON_DRVH3 were bridged together. This is probably why I had PP3V8AON fluctuating between 3.0 - 3.2V instead of getting 3.8V when board didn't want to come on.

I feel lucky on this one...I could just never find the issue.