Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, proposed preliminary checks (if have not been tried):
Still, the described symptom almost always point to an internal hardware issue or more particularly, possible suspects are:
All of the above would require that the unit be opened up for visual inspection, voltage/continuity/resistance checks, confirm faults and effect repairs.
I realize that the above information may perhaps be not what was expected. Unfortunately, there is no quick-n-easy fix and neither is there a workaround; sorry for having to be the bearer of bad news.
Please post back how you would want to approach this and/or should additional information be needed.