820-00840-A - No Display - Liquid damage

[Anterweb]

Got this one in today a1708 820-00840-A .

I was told it stopped working after a drink was spilled on it.

Never been opened before so I'm the first person to ever crack this open.

A few small signs of liquid ingress ( Coke, coffee or something brown and sticky ) around the wifi card and just behind the usb-c ports .

Must have been recent as it all cleaned up real easy and is now spotless and also bottom of the board whole logic board now looks like new!

It draws a solid 20v and normal amps with the battery connected and disconnected.

on power on I get fan spin and trackpad click and also feel the CPU getting warm but no boot sound and no display on screen or external monitor whatsoever,

I popped a usb stick into both ports and it lights up and flickers briefly ( I presume this is how we test for usb activity? )

advice on where to go from here much appreciated.

 

[2informaticos]

Connect USB macOS and see if flashes constantly, like loading OS.
Also try PRAM reset and check if chime comes on.
What is the CPU core voltage (L7210) after 10-15s?

 

[Anterweb]

USB Tested with drive with os on, Solid light on drive no flashing or activity,

Tried resetting PRAM a few times to be sure (no chime ), and weirdly one time when I had the external HD with the OS connected it actually got a backlight and grey screen light up!!!! ( A sign of life! ) I presumed it was sorted. so disconnected external drive and put back internal SSD, same thing no display, Tried again to remove SSD and do PRAM - multiple times and connected external HD to try to reproduce the screen coming on again but I couldn't .. still dead / no display,.

Checked CPU core at L7210 = 0.65v

I also tried dropping the logic board into a known good donor machine with working screen & keyboard, battery and trackpad, exact same behaviour

 

[2informaticos]

CPU gets correct voltae, so board boots, but gets stuck somehow.
Possibly iGPU problem...

 

[Anterweb]

Anyway of being sure or figuring out where it's getting stuck, Where can I go from here?

Is it worth reflowing the GPU?

I do have a good donor board for this Sat on the bench

 

[2informaticos]

There is no dedicated GPU.
iGPU is part of CPU.
You can try to heat, but Intel is not known for such reaction...

Just in case, try first known good BIOS dump.

 

[Anterweb]

I have a brand new bios chip for this logic (weirdly it's the exact same model board as the last one you helped me with) but before I tool up and swap these bios chips I just thought I'd ask is it common for a bios to be affected by water damage, I've never before thought to try a new bios from a liquid damaged board?

Also I've just noticed with this one I get zero fan spin when turning on unless the trackpad is disconnected then it just blows gradually upto full spin, also l get no caps lock light at all, could this indicate anything else I could look into?

Thanks in advance for the help

 

[2informaticos]

Fan goes high shortly after power on, if no trackpad connected.
SMC expects some temp sensors included into trackpad board.

Sometime BIOS corruption can happen after liquid spill.

 

[Anterweb]

So I swapped the bios chip, sadly same result, same behaviour no display to internal or external display

Is there anything I can try to get this back to life?

 

[2informaticos]

Possibly leakage occured from high voltage to CPU data lines.
Backlight circuitry is just between wireless and USB-C area.
We talk about 45V on backlight output...

 

[Anterweb]

Is that a fancy way of saying it's fucked, give up?

 

[2informaticos]

More or less...
If you can't detect any corroded resistor/capacitor, or affected trace, is waste of time.