HP 310X - Manual (Page 147)

What is the state of the USB light?
for HP Jetdirect 175x external print server/Internet connector for USB
and HP Jetdirect 310x external print server/Internet connector for
USB
The behavior of the USB light indicates the status of the USB
connection. If the USB light on your print server is not ON solid
green, find its state in the list below and click on it to continue
troubleshooting.
OFF
Blinking green
Blinking amber
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