Can you check out my tube analog mic pre and repair?

Lakeland MN

Description

Hi. I have a Fredenstein F609 500 Series Tube Microphone Preamp that partially stopped working. The DI works but the mic input does not. Not sure if it's a tube or connection or what. Looking for someone who knows how to solve these riddles. Mic pre is valued at $690. If it's an easy fix, and you are interested in it, I will sell it to you at a better price or if you repair it but don't want it I can just pay you something for that as well if it's reasonable.