Can Anyone Recommend a Repair Shop for a Yamaha C-2x Preamp?

What state are you in? There are still good shops around the country doing repairs. I have searched out many of them as where I live in HI there are no shops left. If you look on AudioKarma.org a number are listed as supporting the site and you can easily research them.

One of the earlier posters noted this but its important to repeat. You may find that for a few hundred more you can buy a much newer, better preamp that is more modern and reliable. That is easier used than new but depending on what you want you should check out Emotiva, Schitt Audio for starters for direct to consumer new gear at decent prices.

@russ69 availability of transistors is of a lot less deficit than tubes, but you might NOT find the original ones. The replacement transistors must be matched to parameters and sites like Digikey or Newark.com have charts of matching. The average price tag for such repair is in the park of $300 which can also buy you same type of working unit.

@mike4597 This issue should not be too new for any experienced repair tech around your corner so you don’t have to find any specific "audiophile approved" tech.

I bought a C2x in 2003. Used it for about 8 years as my phono preamp by taking the signal out of the tape out jacks.

The input and output RCA jacks of the C2x are mounted on the PCB. Through connecting and disconnecting the jacks sometimes break the solder connection to the PCB. That would be something to look at just in case it applies in your situation.

Technetron Electronics, Inc.   NYC.  

IMHO, this is a better option than putting money into the Yamaha.

https://www.usaudiomart.com/details/650090860-musical-fidelity-m3si-integrated-amplifier-black-faceplate-nib/

I'd make sure the transistors are still available before I spent any money on it.