Rockford Punch 45 no sound

Hello everyone I have an old school punch 45 that I've had for years and I would like to repair it.I have no history on it because it was given to me about 16 years ago or more.I have tested it and it powers on the led turns on but it makes a busing sound I don't know if this is normal.it there schematics or voc check somewhere? Any help is appreciated.
 
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