Greetings can be done with a direct bridge others prefer to use a low resistance or other value that allows the passage of standby voltage ... as indicated the source must be disconnected from the video card and so on .... yes The test will be done with the plate outside the TV chassis, check if the screws that hold the plate to the chassis connect ground points through the chassis and bridge them and then activate the source to measure the voltages ... first of all make sure that the source has no damaged components