What's going on

When sound suddenly stops coming through your external audio system on the LG C3 OLED, the issue usually boils down to a communication breakdown over HDMI-CEC (which LG calls SIMPLINK) or eARC negotiations. As a flagship model in the LG OLED evo lineup, the C3 relies on precise digital handshakes to stream multi-channel formats like Dolby Atmos to soundbars and receivers.

When these protocols stall, the TV may fail to recognize the connected soundbar, default back to internal speakers, or transmit muted audio altogether. Most eARC failures on webOS are software-level handshake freezes rather than permanent hardware failures.

Symptoms people notice

• The soundbar turns on with the TV, but no sound is produced.
• webOS audio settings repeatedly revert to Internal TV Speakers.
• Intermittent audio cutouts during movie playback or gaming.
• Lip-sync delays between screen action and soundbar output.
• Volume controls on the LG Magic Remote fail to adjust the external receiver.
• Browse other common TV problems if your issue spans multiple HDMI inputs.

Likely causes

1. Software CEC Lockup: SIMPLINK protocol state gets stuck after power outages or quick source toggling.
2. Incorrect Audio Routing: Digital Sound Output is set to PCM or Auto instead of Pass Through.
3. Cable Bandwidth Limits: Older HDMI cables fail to handle eARC data rates required for high-bitrate surround sound.
4. WebOS Memory Cache: Temporary audio driver glitches following a webOS firmware update.
5. Hardware Fault: Physical damage or static burnout on the dedicated eARC HDMI 2 port.

Quick checks first

First, verify that your HDMI cable is plugged into HDMI Port 2. While ports 1, 3, and 4 support full HDMI 2.1 bandwidth, only Port 2 features the integrated eARC/ARC audio return channel.

Next, check your settings in webOS:

1. Open Settings > Sound > Sound Out and select Use External Speaker / HDMI(ARC) Device.
2. Go to Advanced Settings and set Digital Sound Output to Pass Through.
3. Enable eARC Support directly beneath the sound output options.
4. Ensure SIMPLINK (HDMI-CEC) is enabled under General > External Devices.

If sound remains absent, test a different Ultra High Speed HDMI cable. Weak or failing cables frequently pass 4K video while failing audio return handshakes.

When it's a real hardware fault

If you have completed power cycles, tested multiple HDMI 2.1 cables, and tried a secondary audio receiver without success, the HDMI control chip on the main logic board may be compromised. Physical strain on HDMI Port 2 can fracture solder joints, or a power surge over the HDMI line can ruin the CEC bus transceiver.

Hardware faults typically manifest as HDMI Port 2 failing to recognize any device at all, or the port dropping video alongside audio signal parsing.

Soft resets vs board/panel work

Resolving eARC glitches almost never requires panel intervention or delicate display teardowns. Always exhaust soft resetting steps first: perform a full power drain by unplugging both the TV and soundbar for a full minute, and test a factory reset of sound settings.

If board-level failure on the mainboard is suspected, replacing the main system board is the standard fix. OLED glass panels are extraordinarily fragile; if hardware servicing becomes necessary, board replacements must be handled with extreme care to avoid flexing the display frame.

Next steps

Begin by carrying out the power cycle and menu configuration steps outlined above. If the handshake issue persists only on one specific audio device, check for firmware updates on your soundbar or receiver.

If you are evaluating whether to repair or replace a display experiencing persistent mainboard controller issues, explore our tech reviews for detailed breakdowns of current display reliability and performance.