15min

Xbox Series X Daughterboard

The starting point to diagnosing a working Series X console is the top daughterboard.
Overview
The daughterboard contains:
Santo SMC Southbridge (Microsoft M1139994-001 T6WD5XBG-0004 Southbridge I/O controller)
USB Ports
PCIe, SATA, disc drive connectors
Ethernet controller and connectors
SPI ROM
Audio driver and speaker
Regulators (5V, 3.3V, 2.5V, 1.8V and 1.1V
4 pin Fan connector
6 pin WiFi board connector
6 pin Accessory board connector (controllers/Bluetooth)
10 pin Nexus (Power/LED/Eject) board connector
44 pin USB front board connector
120 pin Board to Board connector (mainboard to daughterboard)
Xbox Series X Daughterboard
Power On & LED
The daughterboard has an extra Power, Eject and LED board that connects via a 10-pin 0.5mm pitch ribbon cable. 
This board is called the Nexus board. It contains a white power LED, a power button and an eject button. 
Xbox Series X Nexus Board Connector
Bypassing Nexus Board
If you have a damaged connector, ribbon or nexus board (small power/LED/eject board) you can bypass the board entirely.
To get an LED indicator that is normally present on the Nexus board, simply solder an 0603 LED to the middle of the 3 test pads right next to the board connector, with the negative side of the LED pointing away from the connector into the board.
Nexus LED Indicator
Now to power the board on and simulate pressing the power button normally present on the Nexus board, you have a few options.
The first option is to short the power on pin (pin 4 from the left) to ground. A good way to do this is shorting these two pins.
Nexus Power Button
Alternatively you can solder a tactile button to tap and effectively short the Power On pin to ground acting as the power on button. 
There are built in debug button and resistor pads already on the board that you can also solder to. You can add a button to the button pad SW4, and the resistor R170 (anything from 100R to 10K is fine. Then you can press the button to turn on.
Xbox Series X Daughterboard Power Switch
Or you can solder a wire to the output pin of the R170 resistor pad (which is basically connected to the pin 4 of the Nexus board connector) and a ground point, and solder it to any button to act as a power button.
Xbox Series X Debug Power Switch
This is useful to be able to power on, and see an LED, without having a known good Nexus power board, ribbon and/or connector.
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