XO Troubleshooting USB
 One of the USB ports doesn't work
This is typically due to broken connector or solder joint at the affected connector.
All of the USB ports receive power from a common switch, so if a problem with power is localized to one port it is likely due to a broken connector or solder joint at the connector.
The USB signals run directly from the connectors to the CS5336 Southbridge (XO-1)/VX855 Companion (XO-1.5)/USB Hub (XO-1.75). If there is a signal integrity problem, and it is not at the connector, the motherboard must be replaced.
- There is no repair for this motherboard if XO-1/XO-1.5. On an XO-1.75, the hub and its crystal may be replaced.
 None of the USB ports work
If none of the USB ports on a laptop work, even after re-installing the software, then the motherboard needs to be replaced.
- Measure the +5V supply at the USB connector (or across C509 or C551). If it is not present, the USB power switch and current limiter, U56, may be broken. It may be bypassed by a 0 ohm resistor at R466 for testing purposes. If the audio (speakers) is also non-functional, that verifies that the problem is the +5V supply on the motherboard.
 Motherboard signal integrity
The hardware self-test provided by Open Firmware contain a section where test signals for the USB ports are output, allowing signal integrity (eye diagrams) of the traces between the Southbridge and the connectors to be made using an oscilloscope.
 A specific USB drive won't mount
Some models of USB drives may be more compatible with the XO laptop than others. Some USB drives may work with Linux, but not with Open Firmware. Only well-tested USB drives should be used for laptop testing. See USB drive for more details.