My 75” (UN75MU6300FXZA) suddenly just shut off and won’t turn back on

Hi @M. Al

Was there a power outage just before this happened?

Disconnect the power from the TV and then remove the back cover from the TV and first visually check if the fuse and power inlet surge suppressor on the power board are both OK.

Here's an image of the power board in your TV where I've marked the fuse and the "blue" surge suppressor.

(click on image)

If the fuse and suppressor appears to be both visually OK i.e. doesn't look damaged at all- not heat affected etc you will need to test them electrically using a DMM (digital multimeter) and check that the fuse has 0.00 Ohms resistance i.e. it should test short circuit.

If the fuse tests OL or infinite ohms on the meter it has blown for some reason. Hopefully due to a power surge and not a problem in the TV. I can't make out the value of the fuse in the image but it should be something like T5.0A 250V (maybe T6.3A). The value is printed on the board next to the fuse.

If it is blown be sure to get an exact replacement as the T in the rating is important e.g. IF the fuse is a T5.0A 250V DO NOT get a 5.0A 250V fuse as a replacement because it will blow immediately the power is applied to the TV.

Hi @M. Al

If the fuse is OK electrically i.e. either tested with a voltmeter or an Ohmmeter, then you need to check if the power board is supplying the 8.0V DC STB (standby) power to the mainboard.

When the power is connected to the TV, the power board sends an stb voltage signal to the mainboard and it is the mainboard that turns on the red power LED on the TV.

If the stb voltage is OK then the problem is in the mainboard. If there's no stb voltage then the problem is in the power board.

Here's an image that shows where to test for the stb voltage on the power board.

Be safety aware when testing on the power board. There is exposed lethal AC voltage on the board, close to where you will be testing