What's going on

The Samsung S90C is a flagship display in the Samsung OLED TV family, offering premium picture performance and high-bandwidth HDMI 2.1 audio options. However, HDMI ARC (Audio Return Channel) and eARC (Enhanced Audio Return Channel) handshakes can be notoriously finicky.

When your Samsung S90C fails to output sound to your soundbar or audio receiver, the issue usually stems from communication glitches in the HDMI-CEC protocol (which Samsung calls Anynet+), misconfigured audio output settings, or an physical negotiation breakdown between the TV's main board and your external audio equipment.

Symptoms people notice

• Soundbar powers on with the TV, but no audio plays.
• Audio randomly drops out or stutters during Dolby Atmos or 5.1 surround playback.
• The TV forcibly reverts its audio output selection to internal "TV Speaker".
• Volume controls on the Samsung Smart Remote stop controlling the external receiver.
• Audio is noticeably out of sync with the video on screen.
• HDMI Port 3 fails to detect connected audio hardware altogether.

Likely causes

1. CEC Handshake Desynchronization: Anynet+ communication state gets frozen between the TV and external device.
2. Wrong HDMI Input: Plugged into HDMI 1, 2, or 4 instead of the dedicated HDMI 3 eARC port.
3. Cable Bandwidth Limitations: Using an older HDMI 1.4 or 2.0 cable that cannot handle eARC throughput.
4. Incorrect Audio Formatting: Bitstream settings causing decoding errors on your specific soundbar model.
5. Firmware Compatibility Glitches: Outdated Tizen OS software harboring known eARC bug fixes.
6. Main Board Port Failure: Electrostatic damage or physical degradation to the eARC control chip on the S90C main board.

Quick checks first

Before diving into complex menus, perform these basic physical checks:

• Check the label: Confirm the HDMI cable connects directly into HDMI Port 3 on the back of the S90C.
• Reseat the cable: Unplug both ends of the HDMI cable and reinsert them firmly to ensure complete pin contact.
• Test an Optical cable: If you need immediate audio, test an optical (TOSLINK) cable. While it limits audio to standard 5.1 and disables HDMI-CEC volume control, it bypasses HDMI handshake issues instantly.
• Isolate other devices: Disconnect all other HDMI devices (streaming sticks, gaming consoles) to see if another device is corrupting the CEC bus.

When it's a real hardware fault

If you have performed power cycles, swapped to a certified HDMI 2.1 cable, verified settings, and tried multiple audio devices without success, you may be dealing with a hardware issue.

A damaged HDMI Port 3 socket or a failing HDMI controller IC on the main board will prevent ARC/eARC negotiation regardless of software configuration. You can cross-reference similar display board issues in our TV troubleshooting hub.

Soft resets vs board/panel work

Software adjustments and hard power cycles resolve roughly 80% of HDMI ARC handshake failures on the S90C. Resetting the TV's network or sound settings clears persistent system glitches without requiring physical disassemblies.

However, if the HDMI port itself is physically loose, damaged by a power spike, or fails to detect any connected eARC device after a factory reset, the main board requires physical repair or replacement. Main board replacement involves removing the back chassis of your OLED display—a task that should be handled carefully to avoid flexing the fragile OLED panel.

Next steps

1. Complete the recommended CEC power cycle (unplugging devices for 5 minutes).
2. Audit your sound settings (eARC Mode: Auto, Format: Pass-Through).
3. Swap in a certified 48Gbps HDMI cable on Port 3.
4. Read our unbiased hardware teardowns and display comparisons in our reviews hub to understand how Samsung drives its modern OLED main boards.