Broken Nakamichi CA-7A phono

Hi,

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. 

https://www.dropbox.com/s/beafocypf4bawvb/VID_20200216_120837.mp4?dl=0

This is the case whether or not my turntable is attached to the phono input.

I have double checked by connecting my TT to existing my CA-5 and connecting it to CA-7 Aux1/Aux2 (of course very low gain). And, i verified that input on the rear panel is correctly configured.

I have reached out to the seller to see if he can help me out. Can anyone of help me figure out what could be going on here?

Thanks