Epson Stylus Pro 7800 User Manual page 288

Note:
A protection system is provided to prevent improper cartridge
insertion. If you cannot insert the ink cartridge smoothly, the type
of cartridge may be incorrect. Check the package and product code.
6. Hold the ink cartridge with the arrow mark facing up and
pointing to the rear of the printer, and then insert it into the
slot. Do not force the cartridge in further by hand.
Note:
❏ If the Ink check light remains on, this indicates the ink cartridge
may not be installed correctly. Remove the ink cartridge and
then reinsert it as described above.
❏ If you install an ink cartridge in the wrong slot, the ink icon of
the slot that you installed wrong ink cartridge blinks on the
LCD. Make sure that the correct ink cartridge is installed in the
correct slot.
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Maintenance and Transportation