I'm not trying to be snappy here, but until you find a broken proprietary part, and have a means to get another replacement one by quoting some catalog number from the manual, who needs a manual?
Just unplug it, take it apart and see what appears to be wrong.
I take things apart all the time without a manual.
If it is a new object to me, I use care, and when the desired effect is not obtained, I carefully partially reassemble before I start to dis-assemble the o object from a different 'direction'.
I suspect that if you have a belt drive that is no longer being drives, then there are but a handful of options:
The motor no longer is working; does the shaft appear to turn i.e are the bearings seized up - this can usually be fixed with some clean out and re-lubrication
If the motor uses brushes - then the brush graphite has worn too short. Sometimes this can damage the commutator, and that is a pain. Most times new brushes will bring the moto back to life.
The motor may have an integral gear train that is bound up and stuck - unlikley, but a bit of solvent then relube can reduce resistance and allow shaded pole motor type to run again.
The motor output will be a quite small shaft with high rotational speed, and likely rather small amounts of torque.
The belt/print moving screen will move slowly with quite low rotational , and present some friction that will need torque to overcome.
So there will be some sort of speed reducing gear train or drive belt system to sort out the conversions out.
A possibility is a (rubber/leather/nylon backed toothed) drive belt (there may be more than one, although unlikely) is gone from old age, or from being burned through if something became jammed and prevented the belt from moving.
I guess this sort of curiousity in me came from fixing things with experience absorbed along the way.
