820-3787 no power

[ThisIsWes:AASP]

Very clean board. No corrosion anywhere and only minor dust.

Green/amber light but no life. No response to SMC bypass. Checking the rails everything looks good down to pp5v_s5 which is bouncing around from 3v-4.4v. PPVIN_S5_P5V is solid at 12.58v. Almost everything else on U7501 is bouncing around.

SMC_PM_G2_EN - bouncing quickly from .8v-3v.. reball SMC?

 

[2informaticos]

Not yet.
Did you try SMC bypass?
Is possible thet SMC detects an error and power cycles the board.

Check for short and voltage pulse on all secondary power rails (untill CPU VCORE).

 

[ThisIsWes:AASP]

PP5V_S4 - bouncing up to .1v
PP5V_S3 - .14v-.16v
PP5V_S0 - 0v-.03v --- 3ohms to ground
PP3V3_S5 - .8v-3v
PP3V3_S4 - .2v-.4v
PP3V3_SUS - .1v-.4v
PP3V3_S3 - .2v-.4v
PP3V3_S0 - .1v-.2v
PP3V3_S3RS0_CAMERA - .1v-.2v

Any suggestions where to start on PP5V_S0?

 

[2informaticos]

"PP5V_S0 - 0v-.03v --- 3ohms to ground"
Fix that.
You can try injecting voltage, no more than 6V.
Start with 2-3V and set amp limit at max on PSU.

 

[ThisIsWes:AASP]

It was C6422 audio_amp_r.
What causes that to short?

 

[2informaticos]

I saw this problem more on A1502 than A1398 boards.
God bless we can get money so easy on Apple name.