A motherboard is a very complicated thing and there are a lot of things that could go wrong resulting in no sound. It is not possible to determine what part may need to be replaced based on just a symptom description. To determine what is wrong, a technician would have to go in and test the board to componet level, starting with a visual inspection and following up by checking voltages, clock signals, and data and address lines.
Complicating things is that the problem may not even be on the main board. The CVP-207 has a daughter board connected to the main board that is part of the audio generating circuit. What you may want to do is make sure that board is securely plugged in as well as all the other connectors.
To go beyond that, I would strongly advise having a qualified technician look at it. Internally, you are dealing with small surface mount soldered electronic components, which are not easy for a novice to work on. The only other option, guessing at which boards may be bad, could get very expensive. For example, the daughter board, as listed by Yamaha's US parts web site, is $365.79 (Part # XXXXX ).
The main board is part # XXXXX and is listed as "not orderable"
The web site address for ordering Yamaha parts in the US is https://www.yamaha24x7.com/
If you are in another country you should contact the distributor in that country for information on how to order parts. You can find international distributor information at http://www.yamaha.com/