Betamax LCD screen doesn't display after storage?
 

I have a Sony Betamax C7 that has been fired up after a few decades in storage - still works, but the LCD screen at the front faded and died when I started it (it was very dim to start with).
Each time I have started it since, it is a little more faded, now mostly gone. It was working fine when it went into storage - any ideas on what it might be?