Fisher 500-C Fisher Doctor

I have a Fisher 500-C , Fisher Doctor Refurbished a few years ago. While it sounds great, the volume sometimes gets louder/softer. Is this enough to diagnose what is wrong ? Thanks
I left the house for an hour, and now it's working fine...
go out more often
yes, but I hate when people sneak into my house and fix my audio gear while I'm out doing errands...
I had a 500C and a great go to for repair. Feel free to contact me if you need someone with great expertise on the 500C I'll get you in touch with him.