820-00840 not turning on


I have a board from an A1708 which doesn't turn on. No trace of liquid spill.
At first, plugging in the charger gave me 5V only, and around 150mA of current draw.
I figured out that my first issue was that it was missing PP3V3_G3H, and that was due to a short to ground (approx 2 Ohms)
I was able to identify that the rail was shorted to ground by a chip... that is not present on the boardview... ( a rectangle QFN chip somewhere between U2800 and U3900, right next to the USB-C connector).
I replaced it by another one that came from a donor, and my PP3V3_G3H was happy again.
But still 5V on the charger...
So I replaced both CD3215s because I had no hint on which one was faulty.
Then I was able to get 20V on the charger, but... current is somewhere jumping between 10mA and 30mA.
PPBUS_G3H gives me a good 13V
But I get pulses on my PP3V3_S5 rail.
The P3V3S5_EN enable signal also pulses.
And this is where I'm stuck. That enable comes from the PMIC, but I am not much familiar with that circuit, and I'm not sure where to look.
I would assume this is maybe an issue with current sense, or maybe something related to the PGOOD signals telling the PMIC that power is not good, and so, PMIC shutting down the rail.
Any suggestion what to look at from this point ?


SMC bypass doesn't help.
The only other coil that pulses, besides 3V3_S5 is is L7030. All other coils read 0V.


Staff member
Do not check charger coil in this kind of buck/boost converter; is irrelevant, if you get stable PPBUS_G3H.

Check diode mode to ground on all other big coils.