Sound problem on Sony TA-343 amplifier

I have a sony TA-343 Amplifier that has a funny problem. On channel A there is a hummm sound,like high voltage when I connect the speakers (have tried other speaker also).ON the same time on the front output db display the red led's that normally move when you play something is stuck on the third LED. Channel B has sound but very soft and with a cracking sound..not clear at all...any sollution where I ca start looking pleaseee