Connect the old turntable to a free channel on the DJ's mixer. RCA audio cables can be used to make this connection. Cables can be purchased at any electronics store for less than $10. Connect the RCA cables to the output jack on the back of the old turntable. Remember to plug the red male jack of the cable into the red female port on the turntable. Do the same with the white cable. Connect the other end of the RCA cables to an open input channel on the back of the DJ's mixer. Make sure that the colors of cable and port match.
Plug in the old turntable and turn it on. Turn on the rest of the DJ's equipment (amplifier and speakers). Place a record on top of the playing surface of the old turntable. Press the play button on the turntable. Turn down the volume for the channel the old turntable is connected to. Let the record begin to play and slowly turn up the volume. Listen to the record.
Slowly play with the record. Try to do a bit of scratching to see how tense the spring in the motor is. Check to see how easy is it to scratch and how it sounds. Figure out the dynamics of the old turntable by experimenting with it. Each turntable will be different, especially old ones, which is why the DJ must be careful and test it. Avoid wild scratching as the motor in the old turntable will unlikely be able to handle it.