The print head doesn't need to be cleaned on this model. It is more likely that the ribbon is not moving (check that the little thumb wheel does about a half turn on every print), or the new ink cartridge has not been fitted correctly (make sure the ribbon is sitting correctly in the gap and running smoothly over the front of the head), or the platten is not set correctly (the plate opposite the head that the paper runs over).
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If anyone needs a Samsung ER-4915 manual, c-tech has it here:
http://the-checkout-tech.com/manuals/cashregisters/Samsung_ER-4915_dealer_pocket_programming_guide_manual.html
Registerman, February 2011
