Step 1: Create Your Turntable

Bake and frost your cake
Cut out an 8 inch cardboard circle and use hot glue to secure your swivel bearing to the middle.
Then glue another small piece of cardboard to the top (this will help with height so that your turntable will sit above the fondant sides.
Cut out another 8 inch round piece of cardboard and glue on a cheap record mat (not pictured)
Use fondant to create a circle around the turnable (so that you can no longer see the bearing when the 8 in piece is secured)
Use frosting to secure the turntable to your cake.
Make that the turn table floats just above the fondant and does not damage it and moves easily

Step 2: Chocolate Record and Details

Chocolate Record

I took an unwanted 7inch vinyl record and cleaned it thoroughly. You can put a small piece of tape hanging off the edge of the record if you want to make it easier to remove, but you will see a faint outline of the tape when it is finished.
Optional: To create the record label in the center I printed (and flipped horizontally) the image I wanted and glued it onto the record before using colored candy melts to trace the text (see a tutorial for this technique here)
Spread tempered chocolate or candy melts over the record
If you clean off the edge before it dries it will be easier to remove.
After it set a room temperature, I moved it to the fridge and then the freeze before popping it off (it is more likely to crack or curl if the temperature decreases too quickly). If the chocolate layer is too thin it will also crack easily.
If you use silicone to cast a mold of the record and create the chocolate record using the mold you can apparently get it to actually play! See here
When it is done put it directly onto your turntable and test out how it spins.

Create the Details

For the arm I cut a skewer and covered it with fondant. I used the end of a black tooth pick to create the needle.
I used a picture of a turntable for reference and tried my best to duplicate the buttons and knobs in fondant. The turn table I used is a Technics 1200 Turntable and is pictured above.
I mixed silver luster dust with vodka and painted in onto silver pieces.