yoga9 3v3 5v fluctuating

[koby058]

Hi

board model: NM-D992

type c remains on 5v. when i connect it the 3.3VALW and 5VALW fluctuating. can someone please help understand why?
main power rail voltage 13v

till now i have tried:
measured all coils resistance looks ok
replaced RT6585CGQW to a brand new one
replaced all mosfets for 3.3v regulator and the dual mosfet for 5v regulator
happen both on DC power and on battery
issue remains

video

schematic attached

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance to ground of the rails that are fluctuating.

What are the measurements for each?

[koby058]

Hi and thanks for trying to help

on the 3.3v coil 5.87K
on the 5v coil 5.78K

[mon2]

These are not shorted rails. What are the actual voltage values on each of these rails? How badly are they fluctuating? Share the range(s).

[koby058]

i have shared a video. in the first post. is that good enough?

[mon2]

I totally missed that. You are power cycling.

Test if the EN (enable) pins are also pulsing in the same manner or not.

[koby058]

Yes, indeed the enable pins are also pulsing in the same manner

[mon2]

Measure the voltage to ground of:

3VALW_TBTB
VCC3_LDO_PD1
VBUS_TBTA
VBUS_TBTB
+3VSUS

[koby058]

3VALW_TBTB 0v
VCC3_LDO_PD1 3.46v
VBUS_TBTA 0.15v
VBUS_TBTB 5.2v
+3VSUS jumping between 0 to 0.5v

could an corapted EC firmware cause this?

[mon2]

+3VSUS jumping between 0 to 0.5v

Remove all power. Measure the resistance to ground of +3VSUS.

3VALW_TBTB 0v

Measure the resistance to ground of 3VALW_TBTB.

What is the resistance in ohms?

[koby058]

due to a vacation i will update here only in the week after next week

[koby058]

Hi,

3VSUS 1.75K
3VALW_TBTB 6.8K

[koby058]

mon2 i found out tha if i connect the daughter board the chargere is getting to 20v but the laptop powers on and shutting down
i found that if i press the SW1 whih is the novo n switch on the board the laptop turns on but if i stop holding the laptop shuts down, any advise?

[mon2]

Review the pull-up resistor and its voltage on the power button. This on/off line should be parked to a logic '1' state when the button is OPEN / not pressed. When pressed, this line should go to logic '0' to enable the logic board (ie. active low signal).

[koby058]

On the power button i see 3.26v and go to zero when button pressed

just to make the current status clear: when i connect the laptop to AC without battery, the KB light and caps lock light is on, after a minute the laptop is going down and back up (probably it is the bios init process), when it turns on i can see the lenovo screen with some message that it is "finishing update do not power off" and immediately it shuts down.

when it is in this bios init process (without pressing the novo N button) i see the voltage on the power button fluctuating


but if i short the internal switch (novo_N) it is starting to work and trying to boot OS but the original power button does not work .

what do you think ?

[mon2]

lenovo screen with some message that it is "finishing update do not power off"

Ok - did not know this. Appears to me to be a corrupt bios image where the power was lost / removed during a critical time of the reflash process. You may have to remove and reflash the target device out of circuit and then test again.

[koby058]

I have rewrite a new bios (two chips) and also rewrite the EC image using i2c with SUCCESSOR
My opinion is that the fact that the laptop working while the novo button is pressed (or shorted) maybe means it is not related to bios or EC firmware.
what do you think?

[mon2]

But do you see the same message upon when it turns on?

[koby058]

Yes, same message, using the normal power button or the novo N without holding it, will show it for a sec and turn off.
holding novo will show it for 20 sec and then try to boot or asking for boot device

https://drive.google.com/file/d/1pdT...ew?usp=sharing