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Fix a TV that has 120Hz that will not work

We'll check source output, HDMI cable, TV port, and compatibility—or tell you when to call a technician.

Troubleshooting · Home electronics
10–20 min
What you'll need
  • TV remote
  • HDMI cable (Ultra High Speed for 4K120, High Speed for 1080p120)
Step 1 of 7

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Steps

Goal: Confirm the symptom, check source output and cable, then rule out TV port and settings.

Check source and cable

Goal: Confirm the source outputs 120Hz and the cable supports the required bandwidth.

  • Open the source device display or video settings. Set refresh rate to 120Hz.
  • For 4K120, use HDMI 2.1 and Ultra High Speed cable. For 1080p120, High Speed is enough. Reseat at both ends.
  • Good: Source outputs 120Hz and cable supports it. Proceed to Check TV port and settings.
  • Bad: Source not set or cable wrong—fix source and try the correct cable.

Check TV port and settings

Goal: Confirm the TV has the right port and input mode for 120Hz.

  • For 4K120, use an HDMI 2.1 port. Check the TV manual for which ports support it.
  • Open TV Settings > Input. Enable Enhanced or HDMI 2.1 mode. Enable Game Mode if the TV requires it for 120Hz.
  • Good: TV port and mode correct. 120Hz activates. Done.
  • Bad: Still no 120Hz—power-cycle to reset HDMI handshake, or call a technician.

When to get help

Call a TV repair technician if:

  • 120Hz works on one source but not another with the same cable and settings.
  • The TV never shows 120Hz with a known 120Hz source after all checks.

Verification

  • The TV displays 120Hz when the source outputs 120Hz—check TV info overlay or source display settings.
  • The source is set to output 120Hz.
  • The HDMI cable matches the resolution (Ultra High Speed for 4K120) and is firmly connected.
  • The TV input is on the correct port with Enhanced mode enabled.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Source output Confirm source outputs 120Hz; enable in source settings.
  2. HDMI cable and port Use correct cable for resolution; use HDMI 2.1 port for 4K120.
  3. TV input mode Enable Enhanced or HDMI 2.1; enable Game Mode if needed.
  4. Power-cycle Unplug TV and source for 30 seconds; plug back in.
  5. Call a pro 120Hz does not work with known 120Hz source after all checks.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • TV model
  • Source device (game console, PC, etc.)
  • HDMI cable type
  • Resolution and refresh rate attempted
  • Steps already tried

Does the source output 120Hz?

Source must output 120Hz.

Open source device display or video settings. Set refresh rate to 120Hz. Yes: check cable and port. No: enable, then test.

Yes No

You can change your answer later.

Enable 120Hz on source and test

Set source output to 120Hz. Test. If 120Hz appears, done. If not, check cable and TV port.

Done

Is the cable correct for your resolution?

4K120 needs Ultra High Speed; 1080p120 needs High Speed.

For 4K120: Ultra High Speed cable. For 1080p120: High Speed cable. Reseat at both ends. Good cable: check TV port. Wrong cable: try correct cable.

Yes No

You can change your answer later.

Try correct cable and test

Use Ultra High Speed for 4K120 or High Speed for 1080p120. Reseat. Test. If 120Hz appears, done. If not, check TV port and power-cycle.

Done

Is the TV port correct and mode enabled?

4K120 needs HDMI 2.1 port.

For 4K120: use HDMI 2.1 port. Enable Enhanced or HDMI 2.1 mode. Enable Game Mode if required. Correct: power-cycle. Wrong: use correct port and mode, then test.

Yes No

You can change your answer later.

Use correct port and enable mode

Plug into HDMI 2.1 port for 4K120. Enable Enhanced mode. Enable Game Mode if needed. Test. If 120Hz appears, done. If not, power-cycle.

Done

Power-cycle and test

Unplug TV and source for 30 seconds. Plug back in. Test. If 120Hz appears, done. If not, call a technician.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why would TV 120Hz not work?
Source not outputting 120Hz, cable does not support the bandwidth, TV port is HDMI 2.0 only (limits 4K to 60Hz), or game mode is off. HDMI handshake can also fail.
Can I fix 120Hz that will not work myself?
Yes. Check source output, HDMI cable, TV port, and power-cycle. Most issues are settings or port related.
When should I call a technician?
If 120Hz works on one source but not another with the same cable and settings, or the TV never shows 120Hz with a known 120Hz source. The HDMI board may need repair.

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