a2485 / water damage

[zeydullak]

Hey guys,

We have a A2485 Mac book that uses 5.17v and 0a, we measured some voltages on the board and got this result.

U5500 -> U5501 .2
UF400 -> RX421 9
UG400 -> RG012 3.3-3.6
LF000 -> 8.8
LF100 -> 8.8
CF800 -> 0
CR805 -> 0
CR853 -> 0

What could be the problem and what should we do next?

 

[2informaticos]

Not sure what all these readings mean.

Can you say something about PPBUS_AON and 3V8_AON?
Also check all CD3217 LDOs.

 

[zeydullak]

We are missing P3V8AON_EN_R and PPBUS_AON IS 12.33V.

 

[zeydullak]

R5710 is disconnected from the board, is it possible to make a direct connection?
Would we be able to replace it with a similar element or would it have to be the exact match?

 

[2informaticos]

You can bypass it with a solder blob, or tiny wire.

 

[zeydullak]

P3V8AON_EN_R is now restored and it is showing 4.49V. Is it correct voltage? Can you tell us what to check next?

 

[2informaticos]

Do you get 3V8_AON output voltage now?

 

[zeydullak]

We are missing power on 3V8_AON and diode mode to ground is 346ohm.

 

[zeydullak]

R5700 is burnt and the board has a hole in it, I have attached a photo for you to look at.

We also bypassed R5710 with a tiny wire and have power there.

 

[2informaticos]

You probably need to change U5700.
Once removed, be sure no short inside that hole.

 

[zeydullak]

We have a question, If we have a short on the board then we should have amps as well right?

The board is not using any amps currently.

 

[zeydullak]

I have Removed U5700, it looks clean and no visible damage underneath it.
The behavior of the board has not changed and is still using 5.27v and 0a.
Should I return the chip?

 

[2informaticos]

Do you have short on pin 2/R5710 to ground?
If not, be sure to have good continuity to pin 12/U5700.
Then you can try resoldering back original U5700.

 

[zeydullak]

When we removed the U5700 chip the amps went up to 0.08 and after placing it back the amps went back down to 0.00.
Is U5700 at fault here or is it some other component?

 

[2informaticos]

Post U5700 basic voltages: pins 8, 7, 5, 12.

 

[zeydullak]

5 -> .8
7 -> .8
8 -> .0
12 -> 4.4

 

[2informaticos]

"8 -> .0"
No PPBUS_AON arrives to U5700?
Check the trace...

 

[zeydullak]

I understand that this line is missing and we need to find a source element which is generating this line. Basically we have to trace back to the source and understand why source of the link is not working. Is that correct approach? And also one more questions --> how to find the source of this line using schematic board view and pdf document. Thank you.

 

[2informaticos]

That power rail comes from RD590.
Just use search function in schematic and boardview (CTRL+F).