I have just received my Nakamichi CA-7A which I bought from an ebay seller for $900. I was super excited to use it to replace my CA-5, which works great with my Rega TT (Ania MC cartridge) though it has a few issues with balance control.
While the new CA-7 works great with my CD player, Aux (Chromecast Audio), it makes a broken noise (not sure how to describe it, please see this video) as soon as I switch it to Phono input.
Sounds like feedback. Double check to see if your plugged into the correct input and that the switches are in the proper positions. If all is good, then I'm with mc, send it back or negotiate a partial refund to pay for the fix. I bet the seller didn't test the phono stage.
Hard to say, techs charge between $60.00 - $90.00 just to diagnose, then the estimate. Probably worth fixing tho, that is a very flexible preamp. I certainly would contact the seller, explain the situation and see what he offers to start.