The D-line has a setting that blanks the board or returns it to displaying the Time or day and Date. This is called the T0 or Time out to Daytime option.
Pressing the programmming button on the end of the display brings up the 4 options.
The first is the brightness setting (page 5 of manual) This is a value on the far right digit between 1 = faint and 9 = bright
The second option is the serial interface (page 6 of the manual) that deals with format hrs min sec or min sec 100ths or bib rank. The normal setting is SE h2 for min:secsec: 10 100 and 2400 baud data speed
The third option is time out for daytime (page 7 of the manual) This setting should be T0 00 to keep the data frozen until overwritten by a new time coming from the timer or PC
The fourth option is the address setting (page 7) and that should normally be Ad 00
You can move to the next setting by pressing the button when the digits on the far left are flashing. The setting will be saved once you exit after the Address option (4th)
http://alge-timing.co.at/alge/download/manual/D-Line/D-LINE-BE.pdf