Knollbrent, I also have the 402 and use an Anthem D2v that I run fronts via ARC Ref5se thru unity gain. I see you tried running mono and both channels worked, but you don’t mention if you used Balanced or SE connection. Have you taken the cover off to inspect the connections and see if a wire has come loose on the inside of the inputs? Do you have a voltage/ohm meter to check continuity on the inputs external to internal?
I have had a number of Mc amps and pre-amps and have never had issues with jacks but it a possibility. I think you problem is minor since you have confirmed both channels work in Mono.
Call McIntosh tech support, I have always found them to be extremely helpand accomadating. I can’t speak for them but I have sent three items back to them, both out of warranty and was only charged for shipping. 2 came back in brand new packing.
Good luck
I have had a number of Mc amps and pre-amps and have never had issues with jacks but it a possibility. I think you problem is minor since you have confirmed both channels work in Mono.
Call McIntosh tech support, I have always found them to be extremely helpand accomadating. I can’t speak for them but I have sent three items back to them, both out of warranty and was only charged for shipping. 2 came back in brand new packing.
Good luck