The first thing to check is you voltages. If they are correct then you might want to see about a repair person.
Many times the sound is not present due to bad or missing voltages +12,+5, -5 etc. Many times you can put a sound into the input of the sound amp and hear sound from the speaker. That would tell you the sound amp is good and something generating the sound is bad.
I suspect it is a simple fix and you could probably narrow the problem down by simple test and maybe fix yourself.
Once again, check ALL voltages and wiring, check that speaker is working, check the sound amp.