Excellegions

I have a 1987 frans am with the 5.7l tpi and it has the digital gauge cluster, with the sys check button and below that the screen that shows the odometer and such. That odometer screen works because I can see the numbers moving, but the screen isn't lit up. Before I go back there blind not really knowing what Im looking for, can anyone tell me what I need to fix that? Is it a bulb that I need to change? Do I have direct access from the back? Or is it not that easy?