Just purchased a used Yamaha S80 online and entire thing is in great shape and screen/all buttons/menus function correctly. However, it produces zero sound signal from any of the outputs, including headphone jack. Ive performed a master reset to factory settings as well as troubleshooted through many owner-manual suggested routes, including making sure all voice, inter-voice, and master volume levels are all at 127, Local switch is On, eq filters are all zero’d, all volume faders up full. No sound on any patch. Is this perhaps an issue with the output amplifier board? Or power supply to that board? I checked the ribbons and they are all connected. Anybody have any clues?