Doesn't work

USB input

• Replace other USB cable with magnetic ring.
• Restart the computer, reconnect the device, and select the correct sound output device name (e.g. Fosi Audio K5 PRO).
• Reinstall the USB driver if necessary. If using a PC, it's recommended to use the USB port at the back of the computer.
• Try a different USB port.
• Try connecting the device to a different computer.
• Ensure that the playback format is adjusted to a maximum of 24-bit/96 kHz.
• Note: Your own other usb cables have to support OTG function.
• iPhone: K5 PRO-> Use a USB C to Lightning OTG Cable ; Q4->Use a USB B to Lightning OTG Cable.
• Android: K5 PRO->Use the included Cable, the 2 in 1 USB Type-C connector must be inserted into the audio source; Q4->Use a USB B to TYPE C Cable.

OPT&COA input

• Be sure to connect the OPT output port (not IN) from audio source, and check if the side of the cable is emitting a red light.
• Ensure the optical cable is firmly inserted into the OPT input port with a buckling sound.
• Select the OPT mode on the DAC, and set the audio output of the TV to PCM mode while turning off other audio effect options such as Dolby or DTS.
• Choose Fosi Audio "Digital Output" as the audio output device.
• Make sure the optical cable is not bent and the optical port is not loose. If necessary, replace the optical cable.
• Try with another audio source.
• Troubleshoot the COA connection problem as above, ensure that use a Coaxial Cable.

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