Intermec PF8d User Manual page 45

Chapter 3 — Troubleshooting and Maintaining the Printer
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2 Lift the printhead.
3 The Black Mark sensor is right near the front of the printer, just
behind the roller, in a groove that runs from the left side of the
printer to the middle. The sensor optics are visible as a small slit
on the left, and there is a ridged finger-notch to the right.
4 If the sensor is not all the way to the right, put your fingertip in
the ridged finger-notch and slide the sensor all the way to the
right. Do not touch the sensor itself, as natural finger oils may
dirty the optics.
5 Lower the printhead, close the printer, and try printing again.
PF8d/PF8t Printer User's Guide