Casio CZ/ VZ/ FZ - Pro Series

Hi all,
  well I've tried messing around with it some but no luck.  I have 
not tried the midi stuff yet because i dont have the cords to hook it 
up at the moment.  It does hiss and get louder when you turn the 
volume up.  I think i have the local midi off unless there is some 
trick to it im not seeing.  someody said it could be a battery.  Is 
there a battery that could be the issue?  The power seems to be 
fine.  I opened it up and I dont really know what to be looking for 
but it seems that nothing is obviously broken (cracked etc.)  I just 
dont know.  I dont have much experiece so any more information you 
can give me would be great.  Thanks for the help
Marty