What's going on

When HDMI ARC (Audio Return Channel) or eARC stops working on the LG UQ75, the issue is almost always digital communication rather than physical destruction. HDMI ARC relies on the HDMI-CEC protocol—branded by LG as SIMPLINK—to negotiate an audio handshake between the TV's main board and your external audio receiver or soundbar.

On the LG LED TV lineup, software updates, sudden power outages, or switching inputs can corrupt this protocol state. When the TV and soundbar lose alignment, webOS defaults back to internal speakers, grays out ARC output options, or cuts audio completely.

Symptoms people notice

• Total audio silence: Video plays fine, but the soundbar remains silent despite showing an active HDMI connection.
• Speaker flip-flopping: You set the audio output to HDMI ARC, but within seconds or after turning the TV back on, webOS forces the setting back to TV Internal Speakers.
• Volume key lock: The LG remote volume keys show a prohibited symbol or fail to change the volume level on the external receiver.
• Audio dropouts: Sound cuts out for two or three seconds periodically, especially when switching between apps like Netflix and YouTube.
• Mismatched lip sync: Audio trails video significantly over the ARC pipeline.

Likely causes

1. SIMPLINK handshake freeze: The software state managing CEC communication has crashed or become desynchronized.
2. Wrong HDMI port: Plugging the soundbar into HDMI 1 or 3 instead of HDMI 2 (the designated eARC/ARC port on the UQ75).
3. Cable bandwidth limitation: Using an older HDMI 1.4 cable that lacks the bandwidth for enhanced eARC data transmission.
4. Audio format mismatch: Sending an uncompressed Dolby Atmos signal to a soundbar that only decodes basic Dolby Digital or PCM.
5. Corrupted webOS cache: Temporary system files blocking proper peripheral detection.
6. Failed HDMI controller IC: In rare cases, voltage spikes over the HDMI line damage the silicon receiver on the TV main board.

Quick checks first

Before digging into deep menus, check the physical setup. Make sure the cable connects to HDMI 2 on your LG UQ75. Disconnect any other secondary HDMI devices (like streaming sticks or gaming consoles) temporarily to isolate the issue—a rogue secondary device often hijacks the CEC bus.

Next, check your cable. Swap in a known-working High-Speed HDMI cable rated for 18Gbps or higher. If you are experiencing general audio issues across other components, review our TV troubleshooting hub for broader audio signal diagnostics.

When it's a real hardware fault

If you have performed power cycles, swapped HDMI cables, and tried multiple soundbars without success, the hardware on the LG UQ75 main board may be damaged. HDMI ports are directly wired to the main processor board, and electrostatic discharges (ESD) through the HDMI cable can fry the CEC/ARC control chip.

Hardware indicators include:

• Physical looseness or visible bent pins inside HDMI Port 2.
• Complete failure of the TV to detect any HDMI input, not just audio return.
• Persistent graying out of the SIMPLINK menu even with no devices connected.

When the HDMI port controller fails hardware-side, replacing individual port pins is generally impractical. The standard fix is swapping out the main board assembly.

Soft resets vs board/panel work

Always start with soft troubleshooting before opening the cabinet or seeking hardware replacement. A soft reset via power cycling clears the volatile RAM and forces webOS to re-query connected HDMI devices.

If software resets and firmware updates fail, opening an LED TV involves handling sensitive internal boards under high voltage risk near the power supply module. Replacing a main board is doable for experienced DIYers, but you should exhaust all webOS resetting options first. For evaluations on modern soundbars and ARC compatibility, check out our latest hardware reviews.

Next steps

1. Unplug both the TV and soundbar from the wall for 5 minutes (the 'hard power cycle').
2. Reconnect the HDMI cable into Port 2 and boot the system back up.
3. Verify SIMPLINK is enabled in Settings > General > Devices > HDMI Settings.
4. Set Sound Out to HDMI(ARC) Device and Digital Sound Output to Pass Through.
5. If the connection remains dead across multiple cables and audio devices, inspect the TV main board for hardware failure.