Omron NT31 Operation Manuals page 241

System Maintenance
Checking the Backlight
230
S The check screen displays all the dots on the screen: either press anywhere on
the touch panel or wait for three seconds and all the dots will be cleared.
With the NT31C, the display and clearance of all the dots on the screen is re-
peated for each color in turn (red → green → blue → magenta → cyan → yellow
→ white → black).
On completion of the display and clearance of all dots, the NT31/NT31C returns
to the "DEVICE CHECK MENU" screen.
S To abort the LCD check, press the top right corner of the touch panel. The
NT31/NT31C will return to the "DEVICE CHECK MENU" screen.
Check if the backlight functions normally by following the menu operation from the
System Menu shown below.
Select "Device Check".
Select "LCD Check".
Select "Maintenance Mode".
Section 6-11