Picade screen won't power up

Yesterday I assembled my new Picade - everything was working great, but today I’m having problems powering on the screen. At first the screen came on, but wouldn’t stay on - it came on for a few seconds, but then went dark momentarily before powering back up again for a few more seconds (in a loop). Each time it would come up with the “HDMI Input” overlay in the top left, like it does when you press the power switch.

I figured probably the power connector was a bit loose, or there wasn’t enough power (I kept on seeing the undervoltage warning yesterday), so I tried plugging in a separate power supply for the screen and now it won’t power on at all (even when I go back to setup with the flickering / intermittent power that workd earlier today). I’ve removed the screen from the picade case to try and isolate the problem, things I’ve tried so far:

  • 3 different leads and 2 different sockets (as well as powering from the PI / a laptop) - all of them successfully power the PI, none of them light up the backlight on the screen.
  • I’ve checked the voltage across the 5V and GND connectors for the digital audio pins - 4.85V, so there is at least some power to the display driver.
  • I’ve checked the resistance on the GND and PWR pins drops to 0 when the button is pressed, so the butons are definitely attached correctly
  • Plugging into the HDMI on my laptop, it doesn’t appear to be detected as a display

Should the display light up without a HDMI cable attached? What else can I check?

Picture of my setup:

Might be worth dropping an email to support@pimoroni.com to see what they say- they tend to handle these, so I’m usually clutching at straws/relaying second-hand information.