Macbook Pro 3V42 only 30ohms to GND

[audiomodder]

This is a weird one. Got a super damaged 2012 i5 820-3115-B I saved from a ton of water damage. Boots up and works fine now except battery drains to 0% in 1-2 days when turned off. Discovered 30ohms to GND on 3V42 which would clearly cause this.

U7000, U4650, and U6901 all checked out fine. Really worried this might be the SMC. Have a few more caps to check first...anyone have experience with this or know where to look?

[piernov]

Re: Macbook Pro 3V42 only 30ohms to GND

Knowing where was the liquid damage would help. If it was near the SMC, a mild reflow might help but try not to kill it.

[audiomodder]

Re: Macbook Pro 3V42 only 30ohms to GND

liquid damage wasnt near SMC. it was all around U7000...
U2600 (clock chip) could be the culprit just as the much as the smc and caps i guess. But I dont want to reflow anything unless a last resort.

just strange that it works perfect minus the battery discharge issue. Almost thinking of building a FET control PCB or something as a workaround. obviously thats more work though.

[audiomodder]

Re: Macbook Pro 3V42 only 30ohms to GND

after checking some parts and putting caps back I now get no green light BUT it still boots and works like normal on battery(?) and still 30ohms to ground on 3V42...strange.

BC_ACOK ranges from 2.1V - 3V now so Im thinking U7000 is dead. I already swapped in another U6901 and U6900.

Half the time I plug in the charger PPBUS_G3H reads uot a steady 12.55V. Sense circuits check out OK too. ACIN = 4V. Man, I'm not sure what happened :/

[BrickBreaker]

Re: Macbook Pro 3V42 only 30ohms to GND

Hey, I'm working on the same board, same issue! Let me know where you're at and I'll start posting my measurements and such, probably on a new thread.

[BrickBreaker]

Re: Macbook Pro 3V42 only 30ohms to GND

Okay so I just replaced U6900 and U6901, earlier I replaced U6990 and I have 17V on DCin fuse, nothing (0.05V) on pin 5 U6900. Same (0.05V) on pin 4. Less (0.005V) pin 3 and 2. Pin 5 is 0.05V.
Looking at the 3.42 circuit U6990 is getting 17V from DC adapter (this is all no battery attached), although I had to run a wire to pin 4 of U6990 because I had no continuity. Pin 7 was getting 17V but like I say, 0 on pin 4.
So my wire is working, U6990 gets voltage.
Pin 8 - 3.8V
Pin 2 - 3.8
Pin 6 - 0
Pin 9 - 0
Pin 10 - 0

I checked around for shorts, nothing on U6990.
Pin 5 of U6901 is 0V (no surprise, I'm not getting PP3v42). What's strange is that at one point I had 3v42 and started checking for SMC_BC_ACOK b.c I had no light on charger. Then I lost 3v42 again. Thinking that the trace from C6990 to U6990 pin 4 was gone, and because U6990 is not generating 3.42, with vcc present, and no shorts present, that there's more internal damage or else I pulled a bad U6990 off my parts board? Maybe I'll try one more replacement for this chip tomorrow. Good luck audiomodder.

[audiomodder]

Re: Macbook Pro 3V42 only 30ohms to GND

U6990 is definitely /not/ supposed to be getting 17V from DCIN. it is not a step down converter. It gets 3V3 from U6901....
what is your pin 1 on U6990?

"Pin 7 was getting 17V but like I say, 0 on pin 4. "
pin 7 of what??

Please start a new thread, you issues are different from what I am dealing with. You should watch videos on the one wire circuit by Louis Rossman as well, to get a better understanding of it.

[BrickBreaker]

Re: Macbook Pro 3V42 only 30ohms to GND

Okay, started a new thread. Where are you on this one? Replace U7000/ ISL yet?