I got a Pi 4 2 days ago. I attempted to install the Unofficial Ubuntu 18.04 image. This involved booting Raspbian-Lite Buster and using this to update the firmware and then booting the Ubuntu 18.04 image. I managed to boot Raspbian Lite, get wifi working and run rpi-update. The trouble is that it has not worked since. I cannot boot Ubuntu, Raspbian with Pixel, or Raspbian Lite. I have tried 2 different SD cads (4Gb and 64Gb). I have burnt the images with Win32DiskImager and Balena. I have re-formatted the SDs with Windows 10 Disk Manager and guiFormat(a tool for formatting SD cards greater than 32Gb with Fat32). Finally I have done the Firmware repair procedure multiple times and repeated all the tests.
The only other variable is the PSU. I am using my bench supply which is an ATX PC supply, more than capable of delivering 3 amps at 5V. I do not think this is an issue.
When powered on with no SD card the Pi blinks green 4 times in a continuous sequence - this indicates firmware is good I believe.
When powered with an image I see sporadic green flashes and the display shows the rainbow square, then 4 raspberries with some boot output, then blank, then repeat continuously. It also display the lightening bolt (but I have read that this does not indicate power issues at this stage of boot).
Now I am coming to the conclusion that the Pi broke or always was broken, although I do not see that I have done anything to cause that.
Any ideas ? Does this sound like a duff Pi ?