There are various possible causes. Check the following.
(1) Are the connection cables connected properly? Connect the connection cables properly. For details, see "Connecting input terminals" and/or "Connecting output terminals" in the operating instructions.
(2) Are the terminals and plugs dirty? Clean the terminals and plugs before making connections.
(3) Is the master output attenuator level set to -6 DB? Switch the master output attenuator level in the utilities mode. For details, see “Changing the settings” in the operating instructions.
(4) Check the procedure to output audio.
[Select output audio]
Select the sound source used by each channel.
Select the CH1/CH2 input source.
[PC]: Selected when using the Serato DJ software to access tracks loaded on the deck.
[PHONO]: Selected when using an output device of phono level (for MM cartridge) such as an analog player connected to the [PHONO/LINE] input terminal.
[LINE]: Selected when using a line level output device such as a DJ player connected to the [PHONO/LINE] input terminal.
Select the CH3/CH4 input source.
[PC]: Selected when using the Serato DJ software to access tracks loaded on the deck.
[MIC1] or [MIC2]: Selected when using a microphone connected to the [MIC1] or [MIC2] terminal.
[CD]: Selected when using a line level output device such as a DJ player connected to the [CD] terminal.

[Output audio]
The following explains how to output audio of Channel 1.
-Output audio from Master Out.
Set the volume of the devices (power amplifier, powered speakers, etc.) connected to the [MASTER OUT 1] and [MASTER OUT 2] terminals to an appropriate level. Note that loud sound will be output if the volume is set too high.
1. Set the positions of the controls, etc., as shown below.

2. Play the track.
3. Move the channel fader (Figure 8 below) to the rear side.
4. Turn the [TRIM] control (Figure 4 below).
Adjust [TRIM] so that the orange indicator on the channel level indicator lights at the peak level.
5. Turn the [MASTER LEVEL] control (Figure 10 below) to adjust the speaker audio level.
-Output audio from the headphones.
1. Set the positions of the controls as shown below.

2. Press the headphone [CUE] button of Channel 1.
3. Turn the [HEADPHONES LEVEL] control.
Adjust the audio level output from the headphones to the appropriate sound volume.
