Husqvarna Lily 540 and 550 "optima 180 sewing machine" Questions

giving off a strange burning-ish smell (not the typical burning smell). I had this on an old Optima 180 never service before. Only a question of thread dust too trick. Cleaned by a pro and ready again

...optima.Where do I adjust that movement for stich? Everything else working but the foot which moves garment is only going up and down.Reverse engages and there is a litlle movement backwards. Viking ...

...bobbin on viking husqvarna 190 You can get the manual on link below. ...

...Optima 180. Has worked fine for 30 years, but suddenly is stuck on buttonhole. Mum thinks there is dust stuck in all the gears, but I cant work out how to get the back off to get in there. There is ...

Optima-190-180-150-/191517822256?pt=LH_DefaultDomain_0&hash=item2c975a0d30 Generic threading: START TO THREAD WITH PRESSURE FOOT UP. AS YOU THREAD GIVE LITTLE PULLS TO INSURE THERE ARE NO SNAGS. 1

...Optima 180. It was working fine until recent, where the needle has stopped moving up and down. What could this be? The belt? Also how do you open to look inside? Could be seized due to old oil ...