Remove the 10 screws on the back cover

Never touch the section that in the picture is selected in red if the board is plugged in!

Main chip is under black metal heat sink; I attached a temperature probe on the heat sink; device always shut off when reaching 50deg C in my measurements; value may vary depending on measurement devices; but effect was quite repeatable

Reason for overheating could be a) bad thermal conduction/circulation; b) damaged main chip; c) damaged peripheral electronic parts

without schematic and with my limited capabilites in in-deep- circuit study a fix for option c) did not seem feasible to me. Same for option b) as the chip is a large QFP - replacement was not a real option for me. So option a) remained. As TV worked remarkably longer just without rear cover, I assumed solution could not be too far away.