Vintage Synth Repair

>> Suddenly my Odyssey MKIII is not working properly. I can hear the
> normal hiss from the unit
>> at normal volume and when I press the keys I can hear that normal
> low end clicking sound
>> but the tones out of the oscillators and noise generator are
> practically gone.  I can still hear
>> the oscillators working at a very very very low volume.

The most likely candidates are:
- Loose contacts somewhere
- some transistor or lowcost opamp that acts as a amplifier need to be  
changed
- some capacitor has losts its value (or shorted out)

Can you still get VCF feedback with resonance at full?
I had an ARP in once that was "dead", but I could get the filter to  
oscillate, and hence the fault was in the signal chain before the  
filter.
You need the service manual to start checking (following) the signals.

tw.