How to get silent Yamaha CP-30 fixed?

Hi Folks, I have an old yamaha CP-30 electric piano that an old friend gave me 28 years ago. It worked back then but has been in storage in my house for about 25 years and when I pulled it out this week it turns on but no sound at all (I don’t have a speaker for it these days but I have working headphones I tried, and we tried patching through to our stereo system but no luck). I tried a bunch of stuff, looked at manual and on the internet but made no progress. I have no electronics knowledge at all and don’t know 1) if it’s worth trying to get equipment this old fixed since I was planning to sell it and 2) if it’s worth fixing where can I find someone who can. I’m not going to keep it was hoping to sell it but was disappointed when no sound came out! Thank you!