LattePanda 3 Delta 684 failing to boot

The unit has been working for a few days since delivery. 

I was test-running a fairly heavy CPU load on it this afternoon, logged in using SSH. After a few minutes I stopped the test from the command line. A few moments later the unit dropped the ssh connection. I could not re-establish connection. I then switched over to the HDMI output from the unit (HDMI cable and keyboard already connected) and got a very corrupted display. I disconnected everything from the unit and let it cool down. Then I tried to start it again.

I restarted the unit and got the same corrupted display. Over multiple trials I got the latte panda logo a couple of times followed by the screen becoming corrupted. Did not get as far as OS boot. I managed to get into the BIOS once, but have not been able to repeat that.

When I hit the power key, the blue LED comes on and the red LED pulses. After a few seconds the red LED flashes twice, and then after a short gap flashes four times. The fan stops running. The red light goes out. The blue LED remains on. There is no video output - so there is no way of telling whether the unit is responding in any way. The lack of fan is very concerning as that heatsink gets hot very quickly.

I think I have a dead board for RMA. Is there anything else I should try?

Thanks in anticipation

    Don