The other day, I flipped on my U20 to find the screen would only show a series of black squares across the top of the screen. It would not respond to any buttons. Also, I noticed when my amplifier was on, the U20 would emit a high pitched "squeal" when first turned on and then fade away.

What might be the possible causes of this? I've had a battery go bad before (I've owned this since new for 29 years!) but it didn't act this way. What else might be causing this issue?