What's going on

If you are searching for an HDMI fix on a Synology router, you are likely dealing with one of two scenarios: either an HDMI-over-IP extender or AV matrix is dropping video signals across your Synology Router Manager (SRM) network, or there is confusion between a Synology network router and a media-focused Synology DiskStation NAS.

Standalone Wi-Fi routers like the Synology RT6600ax, RT2600ac, or WRX560 do not ship with physical HDMI output ports on their chassis. Instead, homeowners and custom installers use HDMI-over-Ethernet extenders to pipe 4K video and eARC audio through the router's Ethernet switch bank. When video cuts out mid-stream, the problem almost always traces back to SRM packet filtering, IGMP multicast settings, or bandwidth shaping choking the video stream.

For broader networking issues, check our main router problems guide or browse tested networking gear in our hardware reviews hub.

Symptoms people notice

• No Signal message on display: The TV or projector reports no video feed from the HDMI-over-IP receiver connected to the router network.
• Video freezes after a few seconds: The display brief shows video, then freezes or drops to black—a classic sign of unhandled multicast traffic.
• eARC / CEC loss: Smart audio return or remote control commands fail between soundbars and matrix switches routed through SRM.
• Router responsiveness drops: The SRM admin interface slows down or crashes when the HDMI network extender is actively transmitting.
• Unrecognized USB device: Plugging a USB-to-HDMI display dongle into the router's USB 3.0 port results in a storage error or no device detected.

Likely causes

1. Disabled IGMP Snooping: Without IGMP Snooping enabled in SRM, video multicast data floods every port on the network, causing severe packet loss and dropping the video stream.
2. Network/Port Isolation: The HDMI encoder and decoder are on separate VLANs or isolated guest subnets that cannot talk directly to each other.
3. SRM Traffic Control limits: Quality of Service (QoS) rules or upload/download caps are choking the sustained 100Mbps–1Gbps bitrate required for uncompressed network HDMI.
4. Unsupported USB peripherals: Synology routers use USB ports exclusively for external storage, cellular dongles, and printer sharing—not display output.
5. Port speed negotiation failure: A bad Cat5e/Cat6 patch cable forces the router port down to 100Mbps Fast Ethernet, which lacks the headroom for HD/4K video.

Quick checks first

• Direct-connect test: Plug the HDMI source directly into the TV display using the same HDMI cables to confirm the physical source and screen work fine before blaming the network.
• Verify port link lights: Check the green and amber LEDs on the Synology router's LAN ports. A solid green light indicates a Gigabit connection, while amber indicates a slow 100Mbps link.
• Bypass intermediate switches: Connect both the HDMI transmitter and receiver directly into the Synology router's main LAN ports, bypassing secondary unmanaged switches.
• Check device power: Confirm that active HDMI-over-IP hardware modules are powered by their dedicated 5V/12V DC adapters or proper PoE ports.

When it's a real hardware fault

If you have verified that your SRM settings are correct and individual Ethernet runs test fine on other devices, the issue may lie with failed hardware. HDMI-over-IP extenders generate significant heat and are susceptible to surge damage over long cable runs. If the indicator lights on the transmitter or receiver stay dark, or if the Synology router refuses to detect a physical link on a known-good LAN port, the PHY chip on the router or the media extender's chipset may have suffered electrical degradation.

Physical port damage on the router itself—such as bent pins or blown Ethernet transformers—requires specialized board repairs. In most home setups, replacing damaged media converters or using a dedicated unmanaged Gigabit switch for HDMI traffic is far more cost-effective.

Soft resets vs board/panel work

Before assuming a hardware failure, start with a controlled software reboot of your network infrastructure:

1. Power-cycle sequence: Unplug power from the Synology router, the HDMI matrix/extenders, and the video source. Wait two full minutes.
2. Boot order: Plug in the Synology router first and wait for the front status LED to turn solid green. Next, power on the HDMI extenders, and finally the video source and display.
3. SRM Soft Reset: If settings are corrupt, press and hold the physical RESET button on the back of the Synology router for 4 seconds until you hear a beep. This resets network administrator credentials and port bindings without erasing your entire system config.

Component-level board work on router mainboards or micro-soldering HDMI chips on proprietary switches is not recommended for DIY repairs. High-frequency video and network traces require precise impedance matching that cannot be replicated with a standard soldering iron.

Next steps

If tweaking IGMP Snooping and clearing bandwidth limits in SRM restores your video stream, your router hardware is perfectly healthy. For persistent network drops across other equipment, explore our detailed router troubleshooting matrix or look into dedicated managed switches reviewed in our hardware reviews hub.