TCL QM7 QLED Mini-LED TV has sound but no picture

The checks in more detail

Cycle through the inputs with the Input button and look for the one with the source. If a game console or PC is connected and the picture is black or flickers, turn it off, switch the TV to the input, turn the device on again and let it renegotiate; lower the device's output to 4K at 60 hertz as a test, because a mode that the cable or the port cannot carry gives a black screen. Try another HDMI port and a certified Ultra High Speed cable. The QM7's local dimming can also confuse a quick judgment.

In a dark room with a dark scene, the screen may seem black because the dimming zones have switched off and the picture is dark; look at a bright menu to check. Turn off any setting that dims the screen, such as Auto brightness or Energy saving, and check Settings, Display and sound, Picture, Backlight, in case it was set to zero. A TV that has just been updated may be applying the update; leave it alone for ten minutes. A soundbar connected with eARC can stop the picture if the CEC handshake loops, so unplug the HDMI cable from the eARC port for a test.

If the whole TV, including the home screen, is black and sound works, hold the power button for thirty seconds with the TV unplugged and try again. If the home screen is black and a faint picture can be seen in a dark room at an angle, the Mini-LED backlight or its driver has failed and needs service. For a TV in warranty, contact TCL with the model number and serial number from the back and describe what you did. Do not open the TV, since the boards hold dangerous voltage. Keep it updated when it works, through Settings, System, About, System update.