No Sound

First of all the obvious - Do not open up the system unless:
1. you have some experience with electronic repair.
2. you're out of warranty.

If under warranty or over your head you can still try connecting the system to a known working speaker, just to rule that out. Other wise take it back to the shope you bought it from, or consult a repair person.

If both 1&2 apply to you check the following suggestions:

1. Feed in a signal, as such from an audio generator, and follow the signal path with a scope. Where the signal stops, is your dead area.

2. Take care that you properly check the power supply. Use a scope to see where the audio signal stops along its path to verify.

3. The output IC is most likely defective, and some of its support
components along with it. You have to try the IC to test. If the cause
of it blowing is not fixed, the new one will blow right away.

4. there is a transistor on the main board which goes bad on these.
Near the center of the board, you'd see the overheated area.

5. RCA has a nack of using low value resistors as fuse devices in these sets, when an output device fails or overloads it normally will open the associated resistor (fuse).

Fix it and crank it up ;]