Designjet 500 constantly tries to unload media

We just bought a belt from u guys to replace a 24" 500 plotter. Before the belt arrives a new staff messed around with the plotter and jam a 7 page bond paper, after we removed the jam the plotter just keep on rolling backwards. What could be the problem. No error code is shown, it just spinning backwards all the time. If in case a component giving the problem, do you have a replacement part that we can buy. Thank you so much.

The plotter is trying to unload the paper.  There is only one sensor that is looking for the front edge of the paper to go by and it isn’t seeing it.  Either there is still some paper at the sensor or the plastic flag on the sensor is now missing or broken.  The part is here: DESIGNJET 500 MEDIA SENSOR and the instructions on how to access the part are in the manual that came with the belt kit.  If you did not buy the belt kit, the manual can be downloaded from: MANUAL