MacBook Pro / Model A2991 / Board 820-02935-A / 20v .20s / Water Damage.

[zeydullak]

Hello,

We have a A2991 MacBook Pro with a Board 820-02935-A that has some water damage around PPBUS_AON_LUXE and around PPVIN_P3V3SD, when connected to charge it uses 20V and .20A but after some time the USB Tester restarts and continues to restart.

What should we be checking first?

I attached some photos to paint a clearer visual for you.

Regards,
Zeydulla.

 

[2informaticos]

What schematic are you using?

 

[zeydullak]

820-02935 051-08286 Rev 5.0.3 for Apple MacBook Pro

​

 

[2informaticos]

OK, I didn't know was available.

Did you check if all small components (resistors) affected by corrosion still have correct values?

Also check diode mode to ground on all secondary power rails.

 

[zeydullak]

I am sharing schematic for this board with you. Please have a look.

How we should know the correct values for components affected by resistors? Where it is written? Is it available in schematics?

Please also guide how to easily find all secondary level power rails in schematics. thank you.

 

[zeydullak]

I attached file to this threat. See if you can download it. Thanks.

 

[zeydullak]

https://we.tl/t-5aGOxJktQY here is a wetransfer link for the schematics.

 

[zeydullak]

So the voltage on 12v lines are slightly fluctuating for example shows voltage 11.5-12.1 and changes frequently.

 

[2informaticos]

No need of schematic, I already found it.

Locate corroded components in boardview, then find corresponding values in schematic.

"guide how to easily find all secondary level power rails in schematics"
Almost all of them in pages 40-62.
You have other on pages 116, 121 and 127.

 

[zeydullak]

Here is one component that was corroded in the schematic, which values should we be comparing the readings we get, and how do we know which are primary or secondary rails?

 

[2informaticos]

CP817 is 100pF capacitor and I'm sure it can't impede the board to boot.
Just remove it.

PPBUS_AON is the main (primary) power rail.

 

[zeydullak]

PPVIN_P3V3SD -> fluctuates between 10.82v - 12.24v
PPVOUT_LUXE_XW -> 0.008v
P3V3SD_PHASE -> 0.0v
P3V3_AWAKE_SW_S -> 0.0v
P3V3SD_VOS -> 0.0v
PPBUS_AON_LUXE -> fluctuates between 10.82v - 12.24v
PPBUS_AON -> fluctuates between 10.82v - 12.24v
LUXE_COMP ->.510
PP5V_S2_LUXE_VDD -> stays at 0v, jumps to 1.3v for a second before going back to 0v

 

[2informaticos]

You should have more components affected by corrosion; possibly broken traces too.
Accumulated crap under BGA chips also may be a problem.
Even a current, or voltage sensor can break the power on sequence.
Liquid spilled repair can be a nightmare, without solution...