Hey,
Recently I have got this
Dell Inspiron 3568 i5 7th Gen
Vegas/Turis SKL/KBL 15341-1 91N85

*Battery is charging and LED is lighting when it's charging
*5V_S5 and 3D3V_S5 are up
*No short circuit in main power rails
*No short circuit in any coils
*When the adapter/power connected U4001 getting SIO_SLP_S3# and getting down to 0V immediately.
*Power button switch getting 3.3v
*When the power button is pressed SIO_PWRBTN# signal is not lowered to exactly 0V. ( This cause due to the immediate effect maybe)
*X1802 Crystal is working
*When the Adapter is plugged in SPI BIOS 7th pin transmits the data and also when the power button is pressed it's trasmitting.

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*I have tried flashing many compatible BIOS but didn't help.
*Check smaller caps and diodes, couldn't find any short circuit.

you can close the leg to the ground with tweezers on the multicontroller. and to look .
what multicontroller. MEC1404 ?

I was removed PL5101, which is supply 1.2v for DIMMs and PCH, and when the adapter plugged in SIO_SLP_S3# 3.3v present.

Secondary level power rails become active 3D3V_S0 and 5V_S0 also active. The 3-Amber and 5-White error code is also blinking.

I have also checked resistance between the ground and PL5101 DIMM/PCH side, which is 377Ω (when PL5101 is removed).
After removing PL5101 the RT8231AGQW side 360kΩ

RT8231AGQW PU5101 (PL5101 removed)

PGOOD-20mV
TON-0.75v
S5-3.3v
S3-0v
VLDOIN- 192mV
VTT & VTTSNS - 0V
VID- 5.12v
VDD- 5.12v
3-Amber and 5-White LED error code is also blinking

To make sure again PL5101 soldered and the adapter plugged in again SIO_SLP_S3# just come and go like a blink.

RT8231AGQW PU5101 (PL5101 solder back)

PGOOD-5mV
S5-7mV
S3-0v
VLDOIN- 10mV
VTT & VTTSNS - 0V
(All these above values change into actual values for instance when the adapter is plugged in and back to these values)
TON-17v
VID- 5.12v
VDD- 5.12v