Sounds like a similar problem I have had with my SC650. It could be the front sensor faulty or loose. Check the small led on the cutting bed about 250mm from right hand side. It should be lit when working (dimly) and detects the front edge when measuring the vinyl. If not the vinyl just keeps rolling of until the end! I could cure mine temporarily by tapping directly on the bed over the sensor. It took the engineer loads of attempts to find the faulty cable and solve it though. Mutoh will do servicing direct, but ours is covered by contract. If you email me I will get the details of the repair company from the file. I know they work direct because they always try to charge me on each visit.