NorthStar MX500 Operator's & Installation Manual page 183

Engineering Mode
The CDU will go on to conduct a Contrast test. Observe that the
display goes through its full range of contrast from white to black.
Highlight OK then press ENT if it varies correctly or Fail if it doesn't.
Next, the CDU will conduct a Backlight test. Observe that the display
goes through its full range of illumination. Highlight OK then press
ENT if it varies correctly or Fail if it doesn't.
Then, the CDU will conduct a Keylight test. You may need to dim the
lights in the room or shade the keyboard so that you can see the
backlights behind the function and softkeys. Observe that the keypad
backlights go through their full range of illumination. Highlight OK
then press ENT if it varies correctly or Fail if it doesn't. Next, the CDU
will conduct a Beeper test. Listen that the internal beeper activates for
about a second. Highlight OK then press ENT if it varies correctly or
Fail if it doesn't. Finally, the CDU will conduct an External Alarm
test. Listen that the external alarm activates continuously. Highlight
OK then press ENT if it varies correctly or Fail if it doesn't.
Upon completion of the above tests, a Test Results screen will be
displayed. In addition to the visual tests which you witnessed, the
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Operator's Manual
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