I know this question is several years old, but I had the same problem for many years and recently found this online —IT WORKED!! My display is now visible at all times. Hope this fix works for others.
Screen is Too Dim ¶
''You cannot read the display because it is too dim.''
=== The Display is Not Brightened All the Way ===
You can brighten the display by holding down the CLOCK SET button and pressing the ‘volume up’ button. Otherwise, the display depends on how much light is in the room, so it automatically adjusts depending on the brightness in the surrounding area.