How can i fix my Cooper Menvier Scantronic alarm?

I have a 9448+ Scantronic alarm, there is power to it has the numbers on the control panel are backlit,but their is the top display which should glow steadily when mains power is present is not lit up,it is not flashing either,can you suggest what might be the problem,the back up battery is only showing 9v,could this be causing the problem.