Lenovo Ideapad 3 15ADA05 / NM-C821 / It does not turn on

Hello
I have a Lenovo Ideapad 3 15ADA05 with a GS450&GS550&GS750 NM-C821 motherboard, which when I press the power button does nothing. The battery charge LED does not light up either.

I have disassembled the equipment and left only the motherboard without battery.
I have checked if there is a short circuit to ground in the coils, but everything seems correct.

I have taken some measurements and I have:
+3VL ... 3,1V
+5VLP ... 5V
+5VALW ... 0V
+3VALW y +3VALW_APU ... 0,08V
+1,8VALW ... 0V

In QE4:
Pin 1 ... 0,68V
Pin 2, 3 ... 0V

PU401:
Pin 13 ... 3,3V

PU402:
Pin 9 ... 0,8V
Pin 12 ... 4,96V
Pin 13 ... 3,56V

KBC:
Pin21, 85, 112 ... 0V
Pin 26 ... 3,17V
Pin 107 ... 0,80V

Can anybody help me?

Thanks

Measure the voltages on pins 79, 86, 93 of KBC
Measure the voltages on pin 110 of the KBC in the following cases:
to power OFF
with power on pressed
to power "ON".

Machine napisal/-a:Mida los voltajes en los pines 79, 86, 93 del KBC

Pin 79 ... 0V
Pin 86 ... 3V
Pin 93 ... 0V

Machine napisal/-a:Mida los voltajes en el pin 110 del KBC en los siguientes casos:
para apagar
con encendido presionado
para encender "ON".

I don't understand what you mean exactly, but I pass the measurements on that pin, without pressing the power on button and once it has been pressed.
Pin 110 ... 3,3V
When I press power on the value drops to 0V. If I keep it pressed it remains at 0V.
The consumption shown on the source is 0.02A and by pressing power on, it remains the same

Replace the bios and remember to save the old one.
Then remeasure the voltages on the KBC, if they remain the same, replace it.

Do I have to reprogram SPI and KBC, or just SPI?
I take this opportunity to ask which KBC programmer you recommend that is affordable, since currently I don't have any for KBC.
Do you have any link to buy?

Although it took a while for the chip to arrive, it finally arrived. I have replaced PU402 that had been shorted and that is why it did not have V20B+. After replacing I have measured the following voltages:
KBC has already been changed

+5VALW ... 3 ,3V
+3VALW ... 0V
+3VL ... 3,1V
+5VLP (PIN 12 PU402) ... 0V It is normal?

In QE4:
Pin 1 (EC_ON_3V) ... 0V
Pin 2 (EC_ON_3V# ... 3,1V

In KBC:
Pin 79 (APU3VALW_EN) ... 2,7V
Pin 86 , 93 ... 0V
Pin 110 ... 3.1V when I press the power button it drops to 0V and when I release it rises to 3.1V

P.D. An error has occured. The chip placed in pu402 is SY8386 and should have been SY8388C. For that reason it generates 3V instead of 5V at the output.

OKAY. At this moment and after changing, KBC, the damaged and erroneous chip, the board has the following voltages, let's see if someone can help me again.
+3VL ... 3,18V
+5VLP ... 4,77V
+5VALW ... 5V
+3VALW, +1,8VAWL, ... 0V

EC_ON:3V# ... 3V

In KBC:
Pin 79 (APU3VALW_EN) ... 2,70V
Pin 86 (PBTN_OUT#) ... 0V
Pin 93 EC_RSMRST#R ... 0V
Pin 110 (ON/OFF_R) ... 3.1V and when you press the power button the value drops to 0V

Replace the bios and remember to save the old one.

I have reprogrammed the BIOS but there has been no change. Everything remains the same

Are all previously measured voltages still the same?

Machine napisal/-a:¿Siguen siendo iguales todos los voltajes medidos anteriormente?

YES

Measure the resistance to ground on pin 93 of KBC .

Machine napisal/-a:Mida la resistencia a tierra en el pin 93 de KBC.

18,5 K

Without the 3v on pin 93 of the KBC nothing will start.
The measures always lead to a problem at the KBC.

Who generates the 3V of EC_RSMRST#?
KBC itself?
Should I change the KBC again in case it has been damaged?

I correct myself EC_RSMRST# must be at 1.8v check RC3198, CC8783, CC1316.
Measure the voltages on all pins of QC11.

Machine napisal/-a:I correct myself EC_RSMRST# must be at 1.8v check RC3198, CC8783, CC1316.

Everything is ok, But at 1.8VALW I have 0V

Machine napisal/-a:Measure the voltages on all pins of QC11.

QC11 on this board is not present, but all the pins have a value of 0V

On pin 27 of PU1901, I have 3.65V. In PR1907, I have 4.8V (+5VLP) on one side and 3.65V on the other end.
I have checked PR1907 and it is ok

Replace KBC.

Excuse my ignorance. NCB is PU1901?
What do the acronyms mean?

KBC (KeyBoard Controller)= chip UE1.