Lenovo Ideadpad gaming 3 15ACH6 not powering on

[questore]

Hi Everyone.

Board number is: LA-L171P Rev: 1A

This laptop came to me as faulty.
After some measurments I have noticed that 3.3V line has 5ohms resistance. After injection, EC was lit up like a christmas tree.
EC removed, Short is gone, and every other line shown normal resistances so I have ordered a new pre-programmed EC

EC come and I have soldered it. (Checked pins 4 times for shorts and connections to pad)
Now when AC plugged in, The following lines come up normal:
+ VCIN1_AC_IN = 3.3V
+3VLP = 3.3V
+ EC_ON = 3.1V
+ 5VALW = 5.1V
+ 3VALW = 3.3V
+ 3V/5VALW_PG = 3.2v
+ 1.8VALW = 1.8V
+ 0.8VALW = 0.75V
+ ON/OFF# (3.3v and goes to 0V for a moment when power button pressed, checked on the EC pin also)

My Problem is that EC_RSMRST# signal stay 0V never rises. (pin nr 100#)
Resistance is 100 ohms after AC plugged in (at NO power state the resistance is 32Kohm)

What could be a problem?
Thanks for any help!

[questore]

Flashed BIOS 3 different bin from here and one from manufacturers site...no change,

[mon2]

Review the clock on the EC. The EC is a stand alone microcontroller (8051 / Arm / Cortex) that needs a clock to operate.

[questore]

Review the clock on the EC. The EC is a stand alone microcontroller (8051 / Arm / Cortex) that needs a clock to operate.

Can you guide me how to do that?

[mon2]

Check the voltage to ground of pin #37 of the EC. This is signal name EC_RST#. This signal should be a logic '1' else the EC is parked in the reset state.

[questore]

Check the voltage to ground of pin #37 of the EC. This is signal name EC_RST#. This signal should be a logic '1' else the EC is parked in the reset state.

EC_RST is 3.2V (High)

[mon2]

Good.

Review this boot sequence. Where does your board fail?

[questore]

Good.

Review this boot sequence. Where does your board fail?

EC_RSMRST never goes high. stays at 0.005v
ON/OF is 3v and when power button pressed goes to 0v for a sec then back to 3v

[mon2]

Not at my desk but check if there is a local pull up resistor on this line. This output signal may be an open drain type and for this reason, the external pull up resistor is mandatory.

[questore]

Not at my desk but check if there is a local pull up resistor on this line. This output signal may be an open drain type and for this reason, the external pull up resistor is mandatory.

RC36 should be that its a 22Kohm resistor but it is not on the direct line of the EC, and no boardview so how do i find it other than continuity check on every 0402 resistor?

[mon2]

Remove all power. Measure the resistance from this signal to +1.8VALW. What is the resistance?

[questore]

Remove all power. Measure the resistance from this signal to +1.8VALW. What is the resistance?

You are right 22k resistance it is

[mon2]

So the mystery pull up is onboard and of the correct value.

What is the resistance to ground of this signal?

[questore]

So the mystery pull up is onboard and of the correct value.

What is the resistance to ground of this signal?

when connected to AC adapter it is 32 ohms

[mon2]

You should never measure resistance or diode mode with power to the device under test.

Remove all power and measure the resistance again.

[questore]

You should never measure resistance or diode mode with power to the device under test.

Remove all power and measure the resistance again.

Understood, thank you. with no power the EC_RSMRST resistance to ground is 32 kohms

[mon2]

So this output signal is not shorted but is also not a logic '1'. Parked in the active low state so keeping the external logic in reset state.

Curious on the voltage to ground measurements of the following (with the power adapter):

EC_SMB_CK1
EC_SMB_DA1

EC_SMB_CK2
EC_SMB_DA2

Each should be ~3 volts.

What is the voltage to ground of ADP_ID? This analog voltage defines the power rating of the power adapter. If this voltage is not matching the schematic values, then the adapter will be considered to be not suitable to power the board.



Is the vendor for this pre-flashed EC reliable?

[questore]

So this output signal is not shorted but is also not a logic '1'. Parked in the active low state so keeping the external logic in reset state.

Curious on the voltage to ground measurements of the following (with the power adapter):

EC_SMB_CK1
EC_SMB_DA1

EC_SMB_CK2
EC_SMB_DA2

Each should be ~3 volts.

What is the voltage to ground of ADP_ID? This analog voltage defines the power rating of the power adapter. If this voltage is not matching the schematic values, then the adapter will be considered to be not suitable to power the board.



Is the vendor for this pre-flashed EC reliable?

EC_SMB_CK1 = 3.2V
EC_SMB_DA1= 3.2V

EC_SMB_CK2 = 0V
EC_SMB_DA2= 0V

ADP_ID = 1.8V (135W charger correct)

[questore]

EC_SMB_CK1 = 3.2V
EC_SMB_DA1= 3.2V

EC_SMB_CK2 = 0V
EC_SMB_DA2= 0V

ADP_ID = 1.8V (135W charger correct)

Correct me but EC_SMB_CK2 and DA2 should rise after 3VS so they are irrevelant now.

New symptom...
After cleaning every IC I have seen visually corroded with isopropil alcohol 99%, then the EC_RSMRST risen up for 1.7V for 2 second, then went to 0v.
Now UT3 is shorted so I have removed It, but is should not matter i guess cause EN1 and EN2 are not present yet.
Thermal camera shows 3 IC getting warm around normal temp 23 degrees PUV1 UL1 and EC
RTC_CLK also not rising could the problem be that one of the crystal is not oscillating?

[questore]

32.768 khz is OK
I'm not sure but is it possible that maybe RSMRST is there for a spilt second then it goes to 0v?
(Cause when plug in the charger the multimeter is rising for a second but so fastly goes to 0v that maybe i cannot catch it.)