This is a common problem if someone has run the printer without paper in both sides. the rubber roller swells up with ink and stuffs up the whole works. Usually a service is due to fix this.
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If anyone needs a manual for a Sharp ER-1970 cash register,c-tech collective have many here:
http://the-checkout-tech.com/manuals/cashregisters/Sharp2.php
Registerman, October 2010