Dell Precision 7520 - USB Ports & Bluetooth Dead After Power IC & Sub-sequent I/O Chip Replacement

Hi everyone,

I am facing a severe and complex hardware-related issue on my Dell Precision 7520 running Windows 10 Pro (64-bit). Both the internal Bluetooth and external USB ports are experiencing critical failures.

Here is the precise timeline and history of the laptop's repairs, which points to a deeper motherboard failure:

The Backstory & Repair History:

The Initial Failure: The laptop was left unused for 4 days, and the battery completely drained to 0% while Windows updates were pending/running. After that, the laptop refused to power on at all.

First Repair Attempt: I took it to a repair shop. They diagnosed a power rail failure and replaced the Power IC and Power Circuit MOSFETs. The laptop successfully powered back on, but upon receiving it, I discovered that all USB ports and the Bluetooth were completely dead.

Second Repair Attempt: I took it back to the technician specifically for the USB/Bluetooth issue. During this second visit, they replaced the I/O Chip (Super I/O) and attempted to swap the internal Bluetooth/Wi-Fi hardware, claiming the original parts were "non-original" (even though it's a standard Intel card). Even after replacing the I/O chip in this second phase, the USB ports and Bluetooth still did not work properly.

The Symptoms Now:

Device Manager: Bluetooth is completely missing or shows up as an "Unknown USB Device (Device Descriptor Request Failed)" with a yellow triangle.

USB Ports Behavior:

A standard wired mouse actually works when plugged into the USB ports.

However, a wireless mouse (via USB dongle) does NOT work.

An external optical drive (CD/DVD drive) does NOT work at all.

No USB flash drives or external USB Bluetooth dongles are recognized.

OS: A clean Windows installation (formatting) was performed, but the issue persists.

Software Troubleshooting Done (With No Success):

Checked and verified all BIOS settings (USB/Thunderbolt configurations are enabled).

Reinstalled official Dell chipset, USB 3.0, and Intel wireless/Bluetooth drivers.

Checked Windows Power Management settings (disabled "Allow the computer to turn off this device to save power" for USB hubs).

Cleaned up and removed ghost/hidden drivers using Device Manager and advanced tools.

Ensured "Bluetooth Support Service" is running in services.msc.

My Suspicion:

Since internal Bluetooth on this Dell workstation communicates via the internal USB bus, and given the strange power behavior on the external ports (wired mouse works, but power-heavy devices like external drives or wireless dongles fail), this is clearly a hardware power rail or voltage drop issue. Since replacing the I/O chip during the second repair did not fix it, I suspect the initial power surge or the technician's repair left the 5V USB power rail compromised (insufficient amperage/voltage drop), or the PCH (Southbridge/Chipset) USB controllers were partially damaged.

Has anyone experienced this specific failure on a Dell Precision workstation? What specific voltage rails, resistors, or capacitors near the PCH should the technician check since the I/O chip replacement already failed to resolve it?

Thank you in advance!