The printer is jammed. Remove the paper rolls and ink cartridge. Check for anything stuck in the printer. Refit rolls and cartridge, turn key to REg mode. Turn power off at wall for 5 seconds, then back on.
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Anyone looking for a Samsung ER-4940 manual?
Try here:
http://the-checkout-tech.com/manuals/cashregisters/samsung1.php
Registerman
June 2010