My eldest has one of those offshore record players with RCA plugs Line-Out.
(Please don’t judge. He is just now, starting his decent down the rabbit hole…) 
Anyway, the receiver does not have phono in.
When connecting to the receiver with Aux In, nothing. No sound, whatsoever.
Connected to CD In, boom! Music.
Why does Aux-in not work? It should, no?
Any ideas?
Thanks in advance for anyone taking the time to answer.
If I understand the situation correctly, he’s in need of a phono preamplifier between the record player and the receiver. The phono cartridge’s output isn’t sufficient, it needs to be multiplied hundreds of times by a phono preamp. This assumes the record player does not have a built in phono preamp. If it does, the phono cartridge or wiring to the rca outputs is defective.
Thanks! That was my suspicon.
I should have been more clear.
The issue is that the RCA Aux Input to the receiver did not work - no sound.
The RCA CD Player input to the receiver did work.
Aren’t the two inputs the same? I know that Phono In is specific to a turntable without a preamp.
But if the CD input worked, doesn’t this mean that his turntable has a built in preamp?
So then, there was sound in through the CD input.
So why no sound through the Aux in?
In theory Aux Input should have worked, yes?
Thanks again!
Sounds like the Aux input is kaput if the record player’s output sounded fine when connected to the CD input. Yes, the CD and AUX inputs are the same in my experience.
Thanks!