LG's C2/C3 sets are great for 4K120, VRR, and gaming, but the extra bandwidth means a flaky cable or mislabeled port will black out faster than on older TVs. This guide focuses on C-series quirks: making sure HDMI Deep Color is on for the right ports, keeping consoles on HDMI 1-4 (all 2.1), and taming Game Optimizer/VRR when a handshake stalls.
Quick answer
- Use a certified Ultra High Speed HDMI cable — marginal cables fail at 4K120/VRR
- Enable HDMI Deep Color — Settings → General → External Devices → HDMI Input Format, set active port to 4K
- Keep consoles on HDMI 1, 3, or 4 — avoid HDMI 2 if eARC is enabled to prevent handshake conflicts
- Start at 4K60, then enable VRR — get stable picture first, then add high refresh features
- Power on in order — let WebOS boot, then receiver, then console/PC
Symptoms
- Black screen with "No Signal" message after connecting console or PC
- Picture works at 4K60 but goes black at 120 Hz or when VRR is enabled
- Intermittent signal drops during gaming or when switching between apps
- Console shows as connected but TV displays no picture — handshake issue
Quick checks
- Confirm the correct input — On the Quick Input list, verify the console/PC icon sits on the port you're using. If the label is wrong, rename it so you know which HDMI 2.1 port you're actually on.
- Inspect the HDMI cable — Look for sharp bends, kinks, or loose connectors. Use a certified Ultra High Speed cable for 4K120/VRR and reseat both ends until they click.
- Test another HDMI source or display — If you can, plug a known-working device (like a streaming stick) into the same port, or plug your source into a different TV. This quickly tells you which side is misbehaving.
- Restart everything — Power off the TV, the source device, and any receiver in between. Unplug them for 30 seconds before turning them back on.
Step-by-step fix
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Start with a direct connection — If you normally run through a receiver or soundbar, temporarily connect the source straight to the TV with a short HDMI 2.1 cable. This removes one variable while you troubleshoot.
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Confirm the right port for 4K120/VRR — All four HDMI ports on C2/C3 are 2.1, but HDMI 2 also carries eARC. If eARC is enabled, keep the console on 1, 3, or 4 to avoid audio handshakes stepping on VRR tests.
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Toggle Deep Color and Game Optimizer — In Settings → General → External Devices → HDMI Input Format, set the active port to 4K. If the screen is still black, turn off VRR/Game Optimizer, get a stable 4K60 picture, then re-enable VRR.
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Match resolution and refresh rate — Start at 4K60. If that works, bump to 120 Hz, then enable VRR/ALLM. If 120 Hz fails, try 1440p120 to rule out bandwidth or cable issues.
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Power on in a clean order — Let WebOS finish booting, then power the receiver (if used), then the console/PC. C-series sets can cache EDID differently depending on that order.
If it still isn't working
After verifying cables, ports, and basic resolution settings, persistent "No signal" or black-screen behavior usually points to a failing port or a deeper compatibility issue. Document which combinations of source, port, and cable work or fail. Having that matrix ready makes support with LG or your TV manufacturer far more effective and can help justify a warranty repair or replacement when simple fixes are exhausted.
When to suspect the TV, source device, or receiver:
- Source device problem — If the TV shows "No signal" no matter which port you try, but other devices work fine in the same port, the console or streamer may be at fault.
- TV problem — If multiple inputs intermittently lose signal for every device, check for a TV firmware update and consider a full factory reset after backing up your picture settings.
- Receiver or switch problem — If things only fail when a receiver or HDMI switch is in the chain, connect the source directly to the TV. If that works, review the receiver's video pass-through and 4K/8K settings.
FAQ
Q: Why does my PS5 work at 4K60 but goes black at 120 Hz? A: This is usually a cable bandwidth issue. A marginal HDMI cable that handles 4K60 (18 Gbps) may fail at 4K120 (48 Gbps). Try a certified Ultra High Speed HDMI cable.
Q: Should I use HDMI 2 for my console if I have a soundbar? A: No, keep your console on HDMI 1, 3, or 4. HDMI 2 handles eARC for audio, and mixing console handshakes with audio handshakes can cause signal drops.
Q: Game Optimizer won't stay enabled — it keeps turning off A: Disable VRR first, get a stable picture at your target resolution, then re-enable VRR within Game Optimizer. The TV needs a clean handshake before adding variable refresh.
Q: Do I need to factory reset my C2/C3? A: Only if multiple devices fail across different ports after trying new cables. Back up your picture settings first, as a factory reset will erase all calibration.
Scenario example: A PS5 on HDMI 4 worked at 4K60, but after enabling 120 Hz + VRR the screen went black. Moving the PS5 to HDMI 3 with a certified 2.1 cable, disabling VRR to get picture, then re-enabling VRR inside Game Optimizer keeps 4K120 stable. Leaving the eARC soundbar on HDMI 2 avoids extra handshakes on the console input.
Expert tip: A surprising number of no-signal problems end up being a marginal HDMI cable that only fails at 4K or at higher frame rates. Swapping to a short, certified Ultra High Speed HDMI cable is one of the fastest ways to tell whether you are chasing a wiring problem or a device issue.
If you want a brand-agnostic HDMI checklist, see our full HDMI "No signal" guide at /4k-tv-receiver-hdmi-no-signal-checklist.