good morning colleague As you say that you disconnect the LVDS communication from the T-COM, it is possible that the latter is faulty, since if it illuminates the BACK-LIGHT in a short time it indicates that it is giving an order to the MAIN BOARD to protect itself indicating that the latter operates very well ... I have the service manual for this TV but there you will not find a schematic diagram that will take you to check measurements since they usually never provide it, the only thing left is to track the tensions that reach the T-COM card from The MAIN BOARD to see if any one is canceled by short which is protected, at this point you have to be very thorough with any action taken. I hope my humble opinion serve and good luck ... sony_kdl-55hx800_chassis_az1-l.pdf [2.05mb] I hope you serve the manual ... greetings