I have a Yamaha psr-100 it's old but nice. I put new batters in it and turn it on, the volume is so low I can hardly hear the left speaker and hear nothing out of the right speaker. When I run the volume button up all the way it's still so low and the other speaker still doesn't play, I know the right speaker works because I can hear very very faint sounds occasionally! What could be the problem? Oh, I plugged it in with the adapter, no change in sound!