820-2655-A no PP3V8_AON

Hi,

820-2655-A no power issue, narrowed it down to no PP3V8_AON (at polarized caps like C5890 or behind L5800), checked enable and VIN
PPVIN_P3V8AON = 12.20V
P3V8AON_EN_R = 4.5V

Checked sense circuits resistance between N and P, all between 2.5 and 3.5 Ohms when measuring on C5850/C5830/C5810

I measured the mosfets Q5820/Q5821/Q5840/Q5841 to check if they only have continuity in one direction and to check if the gate has no contuity.

My thought process was, since I down own an oscilloscope it is not possible for me to check the switching voltages on PP3V8AON_VSW1/2/3 I cannot reliably check if it is switching the voltage properly by checking it behind the inductors L5800/L5820/L5840.

So after this step I figured there is a good chance that U5700 is the culprit. After replacing, still no change in behaviour. Also, the usb C meter stays at 5.2V 0.0A.

The second page of the 3V8 AON circuit is not completely clear to me and also not all pins of U5700 are familiar. Could the mosfets not be switching properly which drains PP3V8_AON right back into U5700, and thus showing no voltage on the polarized caps behind R5800?

Hope someone can point me in the right direction, thanks.

Did you check diode mode to ground at 3V8_AON?

Don't waste time with o-scope; as no output voltage, no pulse for sure!

Yes Diode mode 0.0V drop to ground, resistance mode 4.5ohm. Looked around online and found resistance around this value mentioned, so assumed it was meant to be so low.

Not at all; you have short to ground!

Alright! I'll inject voltage tomorrow. Since it's 4.5 ohms I expect it to be more downstream. What max amps should I consider on this line? Voltage preferably not near 3.8V I assume?

I tried injecting a bit earlier when I already thought of it as a short and the resistance jumped down to 0.08 ohms as calculated from the PSUs voltage and amperage.

4.2V shouldn't be a problem.
Anyway start with just 1V and slowly increase it.
A good thermal camera should detect the culprit before 3V.

BTW, set amp limit to max on PSU first.