Hi Paul and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, if all external factors have been checked and ruled out, then the described symptom almost always point to an internal hardware issue. More particularly, potential suspects after a review of the repair / Service Manual are:
All of the above would require that the unit be opened up for visual inspection, mechanical/voltage/continuity/resistance checks, confirm faults and effect repairs.
Are you then considering a DIY (do-it-yourself) repair approach? If yes, do you have access to and familiar with a multi-meter and even perhaps a soldering iron?