HDMI handshake problems: no signal, flicker and black screens

HDMI problems tend to look dramatic: no signal, a flicker, a black screen that returns after a few seconds. The cause is usually simple. Follow the steps in order, as Samsung's own HDMI guide recommends.

Step 1: Check power and source

1. Make sure the device (console, laptop, cable box) is on. A laptop in sleep or hibernate sends nothing.
2. Check that the TV's input is set to the port you used. If the device is in HDMI 1, the TV source must be HDMI 1. Samsung notes some devices, such as cable boxes, have more than one source.

Step 2: Reseat and power-cycle

Samsung's order is:

1. Disconnect the HDMI cable at both ends.
2. Unplug the power cords of the TV and the device for at least 10 seconds, then plug them back in.
3. Connect the cable to the device first, then to the TV.
4. If the problem remains, try a different HDMI port on the TV and change the TV source to match.

Step 3: Try another cable

If reseating does not help, try a different cable. Samsung recommends using a certified cable compatible with the device. For modes such as 4K at 120Hz, Engadget says to buy by category. Ultra High Speed cables are certified for up to 48Gbps, while Premium High Speed cables are certified for up to 18Gbps. The HDMI Forum says certified Ultra High Speed cables carry a label on the packaging and the cable name on the jacket. See 4K 120Hz not working.

Step 4: Think about length and in-wall runs

Engadget says there is no official maximum length, and the usable distance depends on the cable, the signal and the hardware at each end. As bandwidth rises, a long cable becomes less forgiving. When a cable hits its limit, the picture does not fade gently. It jumps from fine to broken, showing flicker, bright speckles, audio dropouts, brief blackouts or nothing at all.

• Test with a short cable first. A direct connection from source to display is the best baseline.
• Wall plates, couplers, switches and receivers are extra failure points.
• Active and optical HDMI cables can be directional. Plugged in backwards, they can give a black screen even though the cable is good.
• Before you permanently route a long cable, test the highest mode you plan to use.

Step 5: Run the TV's cable test, if it has one

Samsung TVs include an HDMI troubleshooting function: Home > Settings > Support > Device Care > Self Diagnosis > HDMI Troubleshooting. Samsung says to check the connected ports in order, and notes that the exact menu path varies by model. Other brands may offer a similar test under support or diagnostics settings. Check your manual.

Step 6: Check HDMI-CEC

Engadget lists CEC as a cause of a TV that switches input by itself or turns on unexpectedly. If a device keeps waking the TV or stealing the input, turn off CEC for that device or reseat the cable and update firmware. If you use eARC, note that CEC must stay on.

Step 7: Isolate the fault

1. Connect a different device to the same port. If it works, the original device is the likely cause.
2. If neither device works after the steps above, Samsung says the TV itself may have a problem and to contact service.
3. Install any available software updates on the TV and device, since fixes often arrive that way.

Related: no sound from soundbar over eARC. Catalog examples of Ultra High Speed cables: Belkin Ultra HD HDMI 2.1 and UGREEN 8K HDMI 2.1.