Brother DCP6690CW Service Manual page 399

After the fifth symbol (center) is pressed, the "OK" appears if the adjustment is normally
completed. After approx. three seconds, the machine returns to the initial stage of the
maintenance mode.
NOTE: If the touch panel is improperly pressed or a wrong point is pressed, the "NG"
appears on the LCD. After approx. three seconds, the screen returns to the state in step (2).
Start pressing the five symbols again from the first one (top-left).
If the "NG" appears, repeat this procedure two or three times. If the "NG" persists even
after that, check the touch panel harness for a contact failure, breakage, or short-circuit. If
the "NG" continues to be displayed without any of such problems, replace the LCD unit.
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