Thinkpad E15 Gen2 Intel "lower wattage AC Adapter"

[danny34]

Hello folks,

My Thinkpad E15 Gen2 with i7 had stopped loading and wouldn't start either. I noticed the typical error with the Mosfet QB6. This has become unsoldered.

I soldered it back on and found that the gate voltage was too low and that's why it was getting hot. Then I wanted to replace the UB7. Unfortunately the one I ordered from China didn't want to run.
So I soldered the old one back in and it still has its 18.9V at the output of QB6.
I stuck a thermal pad on the QB6 to cool it down a bit.

Now the E15 is running again, but unfortunately it shows every time it starts:
"The connected AC adapter has a lower wattage than the recommended model which was shipped with the system. To boot with the AC adapter, please connect the AC adapter which was shipped with the system.

Press Esc to continue."

However, the notebook charges even when it is running. However, the battery indicator in the taskbar does not show this. But every 3 minutes the battery goes up 1%.

Where does the motherboard get the signal with the charger?

Schematic: HERE

[mon2]

What is the input voltage to QB5? (First dcin MOSFET)

The UB7 of controller is the original?

Remove all power. Meter in resistance mode. Measure the resistance across the dcin MOSFETS.

Source (1-2-3) & drain (5-6-7-8)
Source (1-2-3) & gate (4)
Gate (4) & drain (5-6-7-8)

Post each measurement. Test QB5 and QB6.

[mon2]

Update your bios.

https://forums.lenovo.com/t5/Gaming-...5172725?page=3

[danny34]

Thanks for the reply.

The input voltage on the QB5 is 20.3V.

UB7 is the original one.

I can test the mosfets later, unfortunately I'm at work right now.

I updated the BIOS yesterday to version 1.62 (September 3, 2024), as well as all drivers including PD drivers.
Then reset the bios again.
Unfortunately that didn't change anything.


EDIT: What would happen if I just bridged QB5 and QB6?

[mon2]

Each part serves a purpose so suggest not to do this. For example, the raw voltage from the power adapter will not enter the main power line which is probably ok since you mentioned the unit functions but the protection circuits that are based on the charger IC / PD controller are no longer able to power off these missing and bypassed mosfets. If perhaps the battery mosfet is leaking then that voltage will collide with the raw power adapter voltage and possibly nuke the external power adapter. A risky thought unless you have a current limited DC lab power supply.

So the 20v3 is a good voltage but of course drops to the lower output which is being sensed as being too low. This sensing may be at the BQ charger level. There is a status line of charger OK -> what is the voltage to ground there?

Based on this rather large voltage drop, these same DCin mosfets are suspects. When you can, check their resistance as noted above. One or both may be defective (since the laptop works).