Threading Up Jones/Brother VX2051?

My wife has just been given a old but excellent working condition Jones/Brother VX2051 Buttonmatic Sewing Machine from a elderly Aunt. It has all the original attachments etc and has been regularly serviced, last time about a week ago and all set up. Unfortunately whilst my wife was about to use it for the first time our Grandson(I suspect) has turned a few dials etc then pulled out the thread. No matter what I try I cannot seem to thread it up correctly/set the dials right as it starts to sew but after about 4/5 strokes it stops sewing and the material is under a lot of tension until I finally release it and there is a birds nest of cotton on the underside. The biggest problem is NO INSTRUCTION MANUAL so I don't really know if I'm threading up correctly & have all the dials set correct. Getting my hands on a Manual seems to be impossible, I think I have more chance with Rocking Horse Droppings!!!!!!!!!!!!!!!! Can anyone help PLEASE. Any & All assistance would be greatly appreciated.