Dell XPS13 9370 with LA-E671P motherboard - power issues, no 3.3V and 5V always on voltages

[Rosen Anastasov]

The computer is the one in the subject. Dead. So dead, that no button, no nothing works. Zero signs of it being live until I open it.

What's verified - the B+ voltage is there at 8.4V.

Battery is probably dead, cause it was a bit over discharged (to 6V). I forcefully charged it directly on the cell terminals to 3.8V per cell. Now it has voltage on the output connector, but it is 7.1V, not 7.6V. Even when connected to the motherboard it doesn't charge. But will look at that later.

The +3VALWP and +5VALWP voltages are missing. Traced them to PU500 and PU501. Both of this have the EN2 at 2.2V, but have the EN1 at 0 volts. So these are not enabled due to the EN1 pin being at 0V.

Tried to trace back the EN1 pint. This is the ALWON line. I think it should come from the MEC5105 IC. But I also see a comment next to one of the ALWON lines saying "Check pull up resistor of SPOK at HW side".

The questions I have are:
1) Who is actually supposed to provide that ALWON and under what conditions?
2) IF this is the MEC5105 - can I get one from somewhere and replace it or it contains some proprietary firmware and the laptop is literally dead?

And to ease the process - here are forum links for the motherboard. This is direct link to a attachment in another thread here - https://www.badcaps.net/filedata/fetch?id=2059001.

[mon2]

Remove all power. Confirm the resistance to ground of the missing power rails +3VALWP and +5VALWP. What are their resistances in ohms? If too low, this may be a root cause for these rails to disable.

+5VALWP is often used by USB ports (Vbus) - check the local load switches.
+3VALWP is linked to the PCH - check the resistance to ground of the CPU / PCH rails.

Each without any power to the board / no battery either.

[Rosen Anastasov]

The 5V rail has kOhms to ground. The 3.3V has 1ohm to ground. Power up the lab power supply at 2V/2A, put it on the test point for the 3.3V and turned on the IR camera. The only component that is heating up is the CPU.

Does it mean that the CPU is bad? I would not expect load from until the laptop is powered up.

[mon2]

Correct. To me, the CPU is shorted. Game over.

You can test the 3v3 rails on the CPU / PCH and it will most likely be also at ~1 ohms to ground. This will confirm the root cause.

[Rosen Anastasov]

Tested the PCH rail - 0.6 Ohm to ground. Removed the cooler, supplied again 2V at the 3.3V always on rail. The CPU has 2 blocks - one bigger and one smaller. The smaller one is the one heating up. Game over it is.

Thanks for the guidance! I would be digging into the power blocks, looking at the wrong places. That kind of help is highly appreciated !