Fisher 500T Receiver

The Fisher 500t is an early solid state receiver. If the tuning knob turns but the dial doesn't move it could be the dial-string, or it could be that the tuning knob has a set-screw that locks it to the shaft. Look for a hole on the side of the tuning knob-should take a small allen-wrench.
If it is the dial-string, you can likely search for a dial-stringing diagram online.
There is almost always a diagram in the service manual, and you should be able to get one for free at the Vinyl Engine (I think that's the site name).
My thought on putting money into these guys is this: If you like it and want to keep it, go ahead and pay someone to get it right. If you're thinking about making it perfect and selling it for big money, the demand may not be there.
People seem to like these receivers so enjoy!

Ths364,
Thanks for your input. I am looking more toward selling than keeping it. I am not looking for big money, but would like to get a fair price for it. I guess my next question would be, would I be better served to list it as is and let an interested buyer fix it, or should I fix it and hope to recoup the cost in my sale price. Would you have an idea of a reasonable asking price for it in either condition?

One just sold on ebay for a little over $200, fully working, average cosmetics. These are nowhere near as collectable or valuable as the Fisher tube receivers.