Diagnosis
A poor connection to the LCD display panel. This is often due to a loose ribbon cable connector on the main control board.
How to Fix It
Unplug the unit. Remove the two screws at the top rear of the control panel housing. Gently lift the plastic shroud. You'll see a flat, gray ribbon cable connecting the display to the board. Reseat this connector by unclipping it and firmly re-inserting it.
If That Didn't Work
The main control board itself may be failing. Intermittent display issues can precede a total control failure. The board is located behind the control panel.
Heads Up
Static discharge can damage the control board. Handle the ribbon cable and board by the edges only. Do not touch the gold connector pins.