On Intel NUC systems using the internal NUC CEC adapter (v8 firmware), the adapter may stop responding to CEC power-on requests after an AC power loss. The system cannot be powered on via CEC until it has been manually powered on at least once. This is a known firmware behaviour rather than a hardware fault.

What Happens and Why

The NUC CEC adapter firmware v8 uses the HDMI 5V detect signal to determine the system's power state. When AC power is fully removed and restored — such as after a power cut or a power strip being switched off — the adapter starts in an uninitialised state. If the CEC bus remains silent for more than 120 seconds while the adapter is in this uninitialised state, the adapter stops monitoring the CEC bus and will not respond to any further CEC commands — including power-on commands from a remote or automation system.

Once libCEC initialises the adapter (which happens when the NUC is powered on and libCEC starts), the 120-second timeout no longer applies and CEC functions normally.

Workaround

After a power loss — manual power-on required once

After AC power is restored, the NUC must be manually powered on at least once before CEC power-on will work again. Once libCEC has initialised the adapter, subsequent CEC power-on commands will function normally until the next AC power interruption.

Preventing the timeout

The 120-second timeout only triggers if the CEC bus is completely silent for more than two minutes while the adapter is uninitialised. In practice, most TV and AV setups generate some CEC traffic within that window — device polling, HDCP negotiation, or CEC heartbeat traffic from other devices. If your setup is very minimal (TV in standby, no other CEC devices), you may be more likely to hit this timeout.

If you need the NUC to be consistently powerable via CEC after AC interruptions, consider using a UPS (uninterruptible power supply) to prevent unexpected AC power loss to the system.

Identifying Which Adapter You Have

• External USB-CEC Adapter: A small black box with three ports — USB-A, HDMI in, HDMI out. Connects externally to any PC via USB.
• Internal NUC CEC Adapter: A board-mounted adapter installed inside a compatible Intel NUC. Not externally visible.

For the internal NUC adapter, the firmware version is shown in the libCEC log output or the cec-client adapter listing.

Related Articles

• NUC CEC Compatibility
• Getting Started with the USB-CEC Adapter
• CEC Adapter — Waking the TV When PC Resumes from Sleep