HELP: Apple LaserWriter 16/600 PS - Paper light is Flashing

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Hi, so I got the printer. It appears to be in a good condition, by looking at the plastic and rubber parts (rollers, belts) it seems to be new. It had some paper in it, the toner was installed, so I guess it was used a little, but not much.

Now the paper light is blinking. I just put a lot of paper in the tray, the paper is still blinking. The manual says:

Paper light ON = Paper cassette is Empty. OK, so the light is NOT ON, and there is paper in the tray. if I take the tray out, the light still flashes.

Paper light OFF =Paper supply is OK.

Paper light Flashing = Printer is ready for sheet of manual-feed paper. OK, so the light is flashing regardless if the tray is in or out, or if I open or close the manual-feed door.

What to do next?

Thanks a lot.