no output from the left channel

Check the left/right balance first, because a muted left channel can produce exactly this result: both stereo channels are audible only through the right speaker.

Correct the channel settings

If using Windows 11 or Windows 10 with a Bluetooth device:

1. Open Start → Settings → System → Sound.
2. Under Output, select the affected speakers or headphones.
3. Open Output settings → Volume.
4. Set Left and Right to the same value, such as 100.
5. Return to System → Sound and turn Mono audio Off.
6. Under the device’s Output settings → Format, select 2 channels, 16 bit, 48000 Hz (DVD Quality) if available.
7. Play a stereo left/right channel test.

Microsoft documents these balance, mono, and stereo-format checks specifically for one-channel Bluetooth output.^1^

For Windows 11, Mono audio may also appear under Settings → Accessibility → Audio. Mono combines stereo into one channel, so leave it off when testing separate left and right outputs.^2^

Isolate the speaker or connection

If the balance is already equal:

1. Connect the speakers or headphones to another phone or computer.
   • If the left side still produces nothing, the speaker, headphone cable, plug, or amplifier is faulty.
   • If stereo works correctly elsewhere, continue with the Windows checks below.
2. Reseat the plug completely.
3. For analog speakers, use the audio-output jack—commonly the green jack—not the microphone or line-in jack.
4. If possible, test another speaker or headset on this PC.

Windows recommends checking for loose connections, using the correct jack, and testing audio hardware as part of its standard sound troubleshooting.^3^

Reset effects and the driver

If multiple speakers or headphones show the same incorrect routing:

1. Open Settings → System → Sound and select the output device.
2. Set Audio enhancements to Off. On older Windows versions, open Control Panel → Hardware and Sound → Sound → Playback, right-click the device, select Properties → Enhancements, and choose Disable all enhancements.^3^
3. Search for and open Device Manager.
4. Expand Sound, video and game controllers.
5. Right-click the audio device and select Update driver.
6. If that does not help, select Uninstall device, then restart Windows so the driver is reinstalled.
7. If Windows does not restore a working driver, install the audio driver for the exact PC or motherboard model from its manufacturer.^4^

If this is Bluetooth and the settings are correct, remove and pair the device again, ensuring both earbuds or speaker components connect when prompted.^1^

References

1. Fix Bluetooth audio only playing in one channel | Microsoft Support
2. Make Windows easier to hear | Microsoft Support
3. [Windows 10](https://support.microsoft.com/windows/hardware/audio/fix-sound-or-audio-problems-in-windows)
4. [Windows 10](https://support.microsoft.com/windows/hardware/audio/fix-missing-or-undetected-audio-output-device-in-windows)