I would not dissassemble your
satellite dish yet. You could dissect your problem into 3 areas.
1. Cable. What happens if you take your receiver outside and connect a short cable to your motor? If the problem disappears, then logically the problem is with the cable.
2. Receiver. Find a friend with a working FTA receiver and swap it out. If the problem goes away, then its your receivers fault, if the problem persists, then its your motor fault. If the problem is with your receiver, try resetting it and clear out all information. Or else reload the software.
3. Motor. see #2 Unlikely the source of your problem if your motor is moving.
If you get a picture, its unlikely your LNB is faulty.