Sorry but the bulb replacement is not a simple as it used to be....The screens on modern sound systems are made up of small crystals that glow when activated by electrical current of very small strength..
These are called LCD Liquid Crystal Displays, or could be very small chips like Light Emitting diodes arranged in an alphabet configuration. I dont know which one your particular amplifyer system has,,,
These dispalys are controlled by a fast scanning oscillator which up dates the screen dispay so fast that the screen display shows the information you need to see.
In fact the screen information is going on and off so fast you dont even know its happening .
Anyway to keep this story short the screen display in your case
appears to have stopped scanning..Its a major repair job...
needs to go to a reapair shop for a cost quote to fix for you.