Only one channel has a sound or unbalanced output

• All cables are securely in place and correctly connected.
• Try different power supply and socket.
• Cross-check left & right speakers and input cable.
• If it has multiple input modes, try other modes to see if the issue persist. If multiple output modes, confirm if the other outputs are working properly.
• Try to connect it to different sources (output stereo, not MONO), output and cables.
• If it is a tube preamp, re-seat the tubes, switch them, try a spare pair of tubes.
• If it has headphone out, the headphones does snap into place properly, try different headphones with stereo jack.

If you have any questions or concerns, please don't hesitate to contact support@fosiaudio.com.