wont record deck b

i have 1 rca the 1st post going to my speakers all fine and the second port is rca to 3.5mm jack for my input so i can record but when i record on audacity it only recored the left deck or the deck that is being cued even if the deck volume is down and the master is down please help

I almost got that. You have a “Y” cable but the speakers get one thing and the computer gets something else?

Which mixer have you got? Model numbers are good. I’ve seen mixers that have mixed performance output and hard-wired outputs for each turntable. Do you have one of those?