My TM Nano SE M2 Plus has been working ok for a few years.

But yesterday the HDMI output stopped working. It powers up from mains off and the HDMI works, but after about five minutes the display on the TV goes blank and there is no sound. I get output from the AV socket all the time.

If the Nano is in standby and switch it on - again no HDMI output.

What can I do to get it working again.