Based on the above, the most likely suspect would be the main board.
Depending on the version, it would be Part Number BN94-07162W, BN97-06298Z or BN94-06882C or some other. Rule of thumb is to order/replace only with an identically numbered board.
Please click HERE. This would give you an idea of the cost of refurbished, used and/or pull-out replacement boards.
A more reliable source (depending on availability) would be ShopJimmy HERE.
Based on the prices of the suspected faulty board, then repairs would seem economically reasonable.
It may be the service fee that would be of a concern depending on the going rate in your location.
...thus would information on independent repair shops serve your need?
Not unless you are 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)?