Match the symptom, then work through the safe checks.
1. What best matches what you observe?
2. Complete only the checks that are safe for you.
Show stop conditions
- An HDMI port is bent, burned, loose, sparking, or unusually hot
- The only remaining step requires opening the TV, receiver, or source device
- A firmware or video-mode change cannot be completed with a stable visible picture
Likely causes
- The TV is set to a different HDMI input from the physical port being used
- The source device is off, asleep, or has not completed its HDMI handshake
- The HDMI cable, adapter, receiver, switch, or port is interrupting the signal path
- The source is outputting a resolution, refresh rate, color mode, or HDMI format the TV or intermediate device does not support
Quick checks, in order
Match the selected input to the physical HDMI port
If the cable is in HDMI 2, select HDMI 2 on the TV and confirm the source device is powered on rather than asleep.
Power-cycle both ends to renew the HDMI handshake
Turn off the TV and source, disconnect power briefly, then start the TV before the external device. This is a standard first check in current manufacturer guidance.
Connect the source directly to the TV
Temporarily bypass an AV receiver, HDMI switch, capture device, dock, splitter, or adapter. If direct connection works, the intermediate device or its supported formats are the focus.
Test another known-good HDMI cable and port
Keep the same source and output format while changing one variable at a time. High-bandwidth 4K/120 Hz modes require a cable and ports that support that mode.
Lower the source video format if the TV says unsupported or invalid
Use the source device's safe-mode or display settings to select a resolution and refresh rate supported by the TV. Manufacturer guidance specifically links invalid or unsupported-format messages to incompatible source output.
Which HDMI message or behavior do you see?
Start with power, the selected input, cable seating, and direct connection. The TV may simply be receiving no usable signal.
Focus on the source output resolution, refresh rate, HDMI format, and any receiver or adapter between the source and TV.
The intermediate device may not pass the source format, HDCP state, or required bandwidth.
The original source device and its video-output configuration are the stronger suspects.
Stop and get qualified help when
- An HDMI port is bent, burned, loose, sparking, or unusually hot
- The only remaining step requires opening the TV, receiver, or source device
- A firmware or video-mode change cannot be completed with a stable visible picture
Official support and model manuals
Use the full model number from the rating label. The manufacturer manual is the deciding reference when codes differ by region or product family.
Frequently asked questions
What does Unsupported Signal or Invalid Format mean on a TV?
It usually means the source is sending a video format the TV cannot display on that input. Sony specifically documents INVALID FORMAT when a computer output resolution is unsupported, while Samsung recommends using an output resolution supported by both devices.
Why does HDMI say No Signal even though the cable is connected?
A connected cable does not prove the source is awake, the correct input is selected, or a valid HDMI handshake completed. Test source power, input selection, direct connection, cable and port in that order.
What does HDMI connection not permitted mean?
Wording varies by device, but it can indicate the current HDMI video or protection handshake is not accepted somewhere in the chain. Bypass receivers or adapters for one test and use a video mode supported by both the source and TV before changing hardware.