Sony TA-E77ESD Needs Repair - Any Advice?

I have a Sony ES TA-E77ESD preamp in pretty good working order, but has some issues:

- Static when volume knob turned
- Digital inputs do not work
- The sound processing goes in and out (sounds as though applied EQ is going "on and off" randomly while using)

Sony nor any other service facility will repair this unit due to its age. Does anyone know of a resource for servicing this unit? Has anyone had similar issues?

It might be time for a new preamp, but this is built like a tank and I'd love to keep it going. 

Thanks for any leads.