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Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, have you tried gently tapping on the left side control panel's MENU and INPUT buttons?
Then it would be an internal hardware issue.
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?
Great on the DIY!
Please post back with clear pictures of the inside circuitry particularly the PCB (printed circuit board) of the side panel control.
Appreciate the pictures.
And yes if even with the control panel board disconnected the symptom persists.
Is the IR & standby light board the same with the side panel control board?
The ' pic 173325' failed to show up.
Still, that "...unplugged the manual buttons to eliminate a stuck button as it did not stop the problem...", then yes; it would confirm a most likely fault with the main board.
The main board would be something like a P/N 151426 similar to the product shown HERE. The replacement board should bear exactly the same numbers as that of the currently installed board.