Epson FX-870 User Manual page 97

Additional Tractor Unit
9. If there is slack in the paper between the push and pull tractors,
place the paper-release lever in the pull-tractor position and use
the micro-feed feature to advance the paper until slack is
removed. Then move the paper-release lever back to its original
position.
10. See that the paper is not crooked or wrinkled; then lock the
sprocket units in place.
11. Reinstall the printer cover.
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Using the Printer Options