HP Ew2400 - JetDirect Print Server Administrator's Manual page 187

Note
HP Jetdirect External Print Servers
Reset the HP Jetdirect external print server by holding down the
Test button on the print server while connecting the power cord.
After a cold reset, your network systems may lose their connection
to the printer.
ENWW
When you attempt to reset to factory default values,
print a Jetdirect configuration page to confirm that
factory-reset values have been assigned.
Troubleshooting the HP Jetdirect Print Server 187