Dell XPS 13 9370 not detecting half of its internal devices, troubleshooting [SOLVED]

[SiO2]

Hi all,

the patient of this week is a Dell XPS 13 (9370) with an i5-8250U in good cosmetic condition but with multiple problems. I'm trying to figure out whether it's worth investing more time or not. Here is the diagnosis:

- device powers up, during POST a missing TPM module is reported
- no boot medium found, not even listed in the UEFI (known good NVMe SSD)
- detects and boots a USB drive only from one of the USB ports (the one on the right)
- boots normally into Windows, performs well
- does not detect the WIFI module, the camera, the card reader and the finger print sensor (see the attached picture)
- SATA and TB3 are unknown, since I have no hardware to test with
- device manager shows only one PCIe port

To me it looks like a problem in the SoC. Or maybe a faulty power rail? I have the schematics but cannot find a candidate for a common source of the problem. Already tried a few different FW versions with no change.

Do you guys have experience with cases like this?

Cheers

[SiO2]

Small update: The PCH_PLTRST#_EC signal stays low and is not released. The signal measures short to ground when the laptop is powered off! It also controls the reset of the mentioned devices, so this could lead somewhere eventually.

[SiO2]

Major update: Found the source of the short on PCH_PLTRST#_EC to be near the TB3 controller. Removed a 0-Ohm resistor which connects the reset line to the controller, resolving the short circuit.

Now the missing devices all show up again ... except for the TB3 port of course, but whatever. More than happy with the situation. Might consider replacing the controller, but it's a large BGA so probably better not mess with it.

This was short and painless but maybe useful for somebody in the future?

Cheers