Found out how to get the burn-in test pattern!

[Falkentyne]

Very useful for testing for dead pixels, color uniformity, backlight bleed (or if you just want to clean the fake pixels (dust!) from your screen, though not as efficient as Eizo Monitor Test or Aida64 monitor diagnostics, at least this method can even work on a console.

First you need to enable the burn-in menu itself (aka the "Factory menu")
1) Power off and hold menu+enter for 5 seconds (NOT menu and exit)
2) Power on while still holding down menu and enter. if you held it for 5 seconds before pressing the power button, you can release them all right away (normal service menu is menu for 5 seconds and power)
3) Press Exit after you get the normal display. You will now see a blue factory menu at the top left, that has much different appearance from the "normal" service menu with the strobing adjustments and HPD settings.
Button #2 becomes a buzzer test or something, and button 3 changes to input selection by default (still functions as enter)
4) Scroll to "BurnIn", change burn in to On. The power light should now show the 'standby' status.
5) press exit, then press input selection to HDMI (it seems only this triggers the test pattern).

When you're done enjoying the lightshow or cleaning your screen, just do what the moving box says:"(Menu and Exit to burn in off).
Then power cycle, enable the regular service menu or whatever you were doing before.