[sgroup] S-50 static output

Hello all, Just acquired an S-50 keyboard and it has a slight problem I hope someone could help with, or at least as heard what mine is doing. All output is static and garbled. Sometimes, it sounds "clean", but usually it produces a noisy output. Tried different cables, speakers, headphones, all the same results. Tried several patch disks, same result. Tried cleaning the jacks, no change. The sound is static across all outputs. The keys itself work, as I hooked it up via MIDI to another module, and had no problems. Again, sometimes (randomly), I will get a clean sound. I have not been able to reproduce it consistently. Has anyone had a similar experience, and what did you do (if anything) to fix? I know it is a 20 year old synth, I'm just hoping to breath some life into it. I had an S-10 years ago, and loved it. Thank you, Bill