@misterbobman This symptom is typical of the tires used in the deck becoming perished and so don't have the traction they should. Eventually the take up spindle can't handle the load presented by the cassette and so stops turning. When that happens the auto-shut off kicks in.
I recommend that all the rubber parts be replaced by a qualified technician. Sometimes you can find kits on ebay that have all you need. In other cases, Russell Industries on the east coast does have tires that fit (which is how I serviced out a Nak 700) but you have to figure out the sizes needed. I suspect that anyone competent servicing tape machines these days knows about Russell Industried but you never know. Here's the link:
belts, pulleys and tires for turntables and tape machines.