Lenovo Yoga C940-14 - will not power up each morning until resetting BIOS

[survivalbloke]

I've got this laptop here which is presenting very odd behavior. It works perfectly fine except every morning, it won't power up. Power button does nothing. Reset button on bottom also doesn't seem to have any effect, but if I disconnect the battery, hold the power button for a few seconds to drain capacitance, when I connect the battery back, I can power on. It will go through RAM training as normal, and eventually boot into Windows. The laptop will work fine all day long, but the next morning - the problem is there again.

Any thoughts?

[mon2]

Remove the battery. Does the laptop function with only the power adapter?

[survivalbloke]

Remove the battery. Does the laptop function with only the power adapter?

It does function without the battery. Also, an observation I made yesterday is that it doesn't need to sit overnight to produce the fault. I noted after only a few hours of sitting, not being used, lid open, the device had powered off. It would not respond to the power button. I disconnected the battery and powered it up and it is now sitting beside me, running perfectly normal - without the battery.
**UPDATE** It powered off after only a few moments and has the fault.

[mon2]

To confirm, the board is unable to work with using the external power adapter only (no battery connected)?

Carefully measure the voltage to ground of CHARGER_CHGOK (pin # 4) on the charger IC @ PU12 with the power adapter connected (no battery).

[survivalbloke]

To confirm, the board is unable to work with using the external power adapter only (no battery connected)?

Carefully measure the voltage to ground of CHARGER_CHGOK (pin # 4) on the charger IC @ PU12 with the power adapter connected (no battery).

No, that is not correct. With battery disconnected and external power supply connected, it will power up. But in this case, moments later, the device lost power and is currently in a fault state "no power, no response from power button". Currently drawing 48ma.

[mon2]

Carefully measure the voltage to ground of CHARGER_CHGOK (pin # 4) on the charger IC @ PU12 with the power adapter connected (no battery).

[survivalbloke]

Carefully measure the voltage to ground of CHARGER_CHGOK (pin # 4) on the charger IC @ PU12 with the power adapter connected (no battery).

You wouldn't happen to have a boardview or schematic for this board would you? I'm trying to locate PU12. While I was looking for PU12, I noticed this @ PU2 (see attached) Also, liquid damage @ U17.

[mon2]

No BV. Yup, always always always start with a visual inspection. That is rule #1 on Rossmann videos. That cat puke / urine needs to be cleaned up with IPA.

PU12 = BQ25710RSNR QFN 32P_4X4

[survivalbloke]

No BV. Yup, always always always start with a visual inspection. That is rule #1 on Rossmann videos. That cat puke / urine needs to be cleaned up with IPA.

PU12 = BQ25710RSNR QFN 32P_4X4

Hey, thank you so much! So, to update you, after I repaired the liquid damage and re-flowed a couple of components, the laptop is working correctly and the fault has gone. Cheers!