I have a Blaser Star 2 (inherited from my Dad in 1990) and user manual.
J0 jam is a failure to pick up paper from the tray and feed it (around the gray curved guide at the back) into the print mechanism. Nothing to do with software.
This is very likely to be due to the rubber rollers which pick up the paper having gone hard and not "sticky". Mine does this periodically, I made a mechanical modification to mine so the shaft with the rollers can be removed from the RHS without needing to strip the printer down. I find rubbing some "brasso" on the rubber renews it (temporarily).
I would be possible to do it with the roller in situ (with the paper tray out).
As I'm rather familiar now with this ancient machine, I'm happy to discuss it with people if anyone is interested. Msg me.