HDMI Over Ethernet Troubleshooting Guide (HDBaseT Not Working, HDMI Extender No Signal, 4K Issues)

HDBaseT not working? Experiencing HDMI extender ‘no signal’, flickering, sparkles, or displays going blank when using HDMI over CAT6? These are some of the most common problems in HDMI distribution systems, particularly when dealing with 4K signals.

We have carried out hundreds of installations and answered support calls from hundreds more, and most faults tend to come down to a few predictable causes: cabling, compatibility, EDID settings, power supply issues, or the use of the wrong distribution technology for the installation. This guide will help you isolate the cause of HDMI extender problems, HDBaseT issues, HDMI flickering, sparkles, intermittent blank screens, and 4K signal compatibility problems.

Quick First Tests for HDMI Extender and HDBaseT Issues

Before assuming a hardware fault, run through these quick tests to isolate the most common causes of HDMI extender issues:

• Check if there is a good signal from the HDMI Loop Out (if present).
  This confirms that the source signal is compatible and that the HDMI lead into the distribution device is working correctly.
• Replace the input and output HDMI leads.
  HDMI leads are a frequent cause of HDMI extender no signal problems, especially when older or uncertified cables are reused.
• Test the CAT6 connection with a short, factory-made cable.
  Use the same display as your HDMI Loop Out test. This is one of the quickest ways to confirm whether the issue is in the installed cabling or elsewhere in the HDMI over CAT6 or HDBaseT system.
• Check EDID settings and refer to the product manual.
  A mismatched EDID setting can cause no signal, flickering, intermittent blank screens, or wider HDMI compatibility problems.
• Reduce the resolution on the source device to 1080p or 720p.
  If only lower resolutions work, a cabling or compatibility issue is likely. This is a strong indicator of 4K signal problems.
• Hard reboot the source device once everything is connected.
  Power the device off fully before turning it back on. This forces it to re-read EDID information during startup.
• Check that the power supply is correct.
  Confirm both voltage and amperage, especially for USB-powered devices where insufficient current can cause unstable behaviour.

Why Cabling Causes Most HDMI Extender and HDBaseT Problems

The most common cause of HDMI extender problems, HDBaseT issues, HDMI flickering, and intermittent signal loss is CAT and HDMI cabling.

Common symptoms of HDMI over CAT6 and HDBaseT cabling problems

• No signal on display
• Flickering or intermittent black screen
• Pixels or sparkles
• Dropped audio
• Video jitter
• Only working at lower resolutions

Your CAT5e/6/7 cabling must be good for HD, very good for 4K, and perfect for 8K transmission. Just because the cable tests OK on a CAT continuity tester does not mean it will be able to cope with the high frequency bandwidth requirement.

The simplest test is to use a factory-produced and terminated CAT6 cable to the nearest TV. A patch lead that was not made by you will not have the same potential error as all the other CAT6 cables you have just pulled and terminated.

Expect lower performance from CAT5e than CAT6 or CAT6a. Cabling that allowed you to transmit at 1080p may not work at 4K bandwidth. If the length of the CAT cable is close to the maximum distribution range of the system, you may encounter issues depending on termination and cable quality.

Poor termination at any point in the transmission chain, including RJ45 connectors, patch panels, and wallplate terminals, can have an impact. Sharp kinks in the cable may also damage the geometry required for high-speed data transmission.

Avoid crossover cables. While some devices auto-correct, many AV products expect straight-through T568B wiring.

A short circuit in one CAT cable can impact the entire distribution system. If there is persistent flashing on all displays, disconnect all CAT cables from the transmitter and add them back one at a time to identify the problem cable.

Flat ethernet cables are a poor choice for devices requiring power over the Ethernet cable. Stick to round twisted-pair cables.

Solutions for HDMI over CAT6 and HDBaseT cabling problems

• Re-terminate the problem cable.
• Check whether the cable may be wired as crossover.
• Gently straighten sharp kinks.
• Run a new cable.
• If cabling cannot be improved, for example because it is plastered in, consider that AV over IP systems may be more tolerant of certain cable issues than HDMI over CAT6. HDBaseT may also perform better than some HDMI over CAT6 systems in this situation.

HDMI Cable Requirements for 4K and 8K Signal Stability

HDMI leads are not all the same. There are plenty of old HDMI cables floating around in boxes and drawers, and you may have picked up an older cable that is not suitable for modern 4K signal distribution. This is what you need to know.

For 1080p HD, you can use an HDMI 1.4 (10.2Gbps) cable from as long ago as 2009. This will carry 1080p and even 4K30Hz, although 4K30Hz is not sufficient for UK broadcast TV. It may have High Speed printed on the cable.

For 4K60Hz, you need 4K certified HDMI cables that comply with the HDMI 2.0 (18Gbps) standard. Passive cables should ideally not be longer than 5m for 4K60Hz, although you may get away with 7m. They may have Premium High Speed printed on the cable.

For 8K60Hz, use 8K certified cables that comply with the HDMI 2.1 (48Gbps) standard. Passive HDMI cables should ideally not be longer than 5m for 8K60Hz, and 3m is a safer target. They may have Ultra High Speed printed on the cable.

You must use the correct standard for both the connection from your source device to the HDMI input on the transmitter and from the HDMI output on the receiver to your display. Both ends matter when diagnosing HDMI no signal issues and 4K compatibility problems.

More recent HDMI standards are reverse compatible, so an 8K cable will also be fine for 4K and HD.

EDID Problems in HDMI Distribution Systems

If it is not cabling, it may be an EDID issue.

Electronic Device ID (EDID) is essentially a set of information provided by a receiving device, such as a TV, to a source device, such as a Sky Q receiver, to communicate what formats and resolutions it can handle. The source device reads this information and optimises its output accordingly.

When you install a matrix, splitter, extender, or multiviewer between the source device and the displays, that device has to manage EDID correctly. If the distribution device is configured with an EDID of 4K60Hz, then a capable source may attempt to send 4K60Hz. If some connected displays only support 1080p, they may not be able to cope with the format being received.

The product manual will advise how EDID is handled and what settings are available.

Set EDID on the splitter, matrix, or switch to match a resolution and audio format that all displays can receive. If you are unsure of display capabilities, start with 1080p and 2-channel stereo, or even 720p, and work your way up until something fails.

Some products have downscaling features. These make it possible to set the EDID to a higher resolution and use downscaling to accommodate older displays.

Power Supply Issues in HDMI Extenders and Wireless HDMI Systems

Are you using the correct power supply?

Some products, particularly wireless HDMI dongles, are USB powered. It is important to understand that these devices require a certain amount of power to function correctly. While USB ports generally provide 5 volts, older USB ports may provide as little as 0.5 amps of current.

If your USB-powered equipment has trouble maintaining a connection, shows picture artefacts, or displays a green or blue screen, it is probably receiving too little power.

Check the power requirement and ensure that it is being met. Use an adaptor if required.

Many products are supplied with external PSUs. It is always worth checking that the correct PSU is being used by confirming the required output in volts and amps. Erratic performance can come down to an incorrect or faulty PSU.

AV Receiver Problems in HDMI Distribution Setups

Is there an AV receiver in your HDMI distribution setup?

AV receivers are frequently involved in complex HDMI distribution arrangements. Make sure you understand how EDID data is being passed down the chain and what, if any, processing is being carried out by the AVR.

Check the behaviour and settings of the AVR when it is in standby mode, or when it considers input and output ports to be inactive.

It may help to bypass the AVR temporarily while you isolate the issue.

Are You Using the Correct HDMI Distribution System?

Is there a router or switch anywhere on the distribution chain? Yes? You should be using an AV over IP solution. No? Use an HDBaseT or HDMI over CAT solution.

HDBaseT is a demanding set of standards for sending HDMI over Ethernet cabling. It requires a point-to-point Ethernet connection and does not operate over standard network switches or routers.

HDMI over CAT performs a similar function to HDBaseT in sending HDMI signals over point-to-point Ethernet cable, but these systems may not meet all HDBaseT requirements in terms of formats, features, range, latency, and power.

AV over IP also uses Ethernet to distribute signals, but it differs from HDMI over CAT and HDBaseT because the encoders and transmitters convert the signal into IP packets which can then be sent through switches and routers before being decoded again by receivers on the network.