lenovo yoga 7-15itl5 after battery breaks

[Honziq]

Hello,

my Lenovo with board GYG41/GYG51/NM-D131 wont turn on.
It has dead battery - 0V, one cell is completly bad.
But it wont turn on even without battery, reset switch didnt help.

It got only 3,3V, 1,8V and 3,7V?? maybe that should be 5V rail idk.

And UU1 (SN1905004YBGR) is getting hot after charger is connected.

Can it be dead UU1 or it is some short behind it?
What should I check?

Thank you for any advice.

[mon2]

If this part is getting hot then perhaps you do have a short on one of the downstream rails. Remove all power. Meter in resistance mode. Measure the resistance to ground on each of the power rails (input / output as well). Hunting for any rail with a low resistance.

That is,

VBUS_TBTA
VBUS_TBTB
VCC3_LDO_PD
+5VALW

[Honziq]

If this part is getting hot then perhaps you do have a short on one of the downstream rails. Remove all power. Meter in resistance mode. Measure the resistance to ground on each of the power rails (input / output as well). Hunting for any rail with a low resistance.

That is,

VBUS_TBTA
VBUS_TBTB
VCC3_LDO_PD
+5VALW

Thank You,

VBUS_TBTA 42,4 ohm
VBUS_TBTB 25 kOhm
VCC3_LDO_PD 35,3 ohm
+5VALW 39,6 ohm

and

3VALW_TBTA 1,7ohm
3VALW_TBTB 1,7ohm

There are no shorts, but 1,7 ohm is suspicious enough?

Should I try to inject voltage in it?

Thank you very much.

[mon2]

VCC3_LDO_PD 35,3 ohm
+5VALW 39,6 ohm

are also suspects. Often linked to the usb ports since they consume the 5v rail for vbus. Do investigate the usb load switches that should be nearby the usb ports. On a bad event, they trigger and cause this rail to tank.

Yes, ok to voltage inject. Keep voltage low and monitor for who heats up.

[Honziq]

VCC3_LDO_PD 35,3 ohm
+5VALW 39,6 ohm

are also suspects. Often linked to the usb ports since they consume the 5v rail for vbus. Do investigate the usb load switches that should be nearby the usb ports. On a bad event, they trigger and cause this rail to tank.

Yes, ok to voltage inject. Keep voltage low and monitor for who heats up.

After 3VALW_TBTB was injected 1V, one of Intel retimers (UU8) heats up, 3VALW_TBTA heats up first retimer for USBC (UU3).
Other rails doing nothing, maybe if I turn voltage up little bit?

[Honziq]

I can’t belive both retimers are bad.
That 5V rail if I inject 1V its only 0,025A, so it can’t heat anything.

Interesting thing is when laptop is connected to charger it draws 1,3w from it and UU1 and UU3 was getting hot (UU3 only little bit), second USB C draws 0,3W and only UU1 was getting hot.

I’m also wondering, if that laptop isn’t designer to work without battery?

[Honziq]

[Honziq]

It looks like the main short is direcrly in UU1 and maybe also in both retimers. But they all are BGA so i can’t prove it by removing that parts. Also it will be problem change retimer I can’t reprogram it.

[Honziq]

After UU1 was removed:

VBUS_TBTA short gone
VBUS_TBTB 25 kOhm
VCC3_LDO_PD short gone
+5VALW short gone

and

3VALW_TBTA short gone
3VALW_TBTB 1,7ohm

maybe I should try to remove UU8 to get rid of that last short and order new UU1 and UU8.

Hopefully it will solve that problem.
I have to learn how to solder it back in place.