LG OLED C4 144 Hz Flicker or Black Screen: PC Troubleshooting Guide

Quick Answer

Treat 4K 120 Hz as the control condition. Connect the PC directly to one C4 HDMI input with a certified Ultra High Speed cable, disable VRR and HDR temporarily, and confirm that 3840 × 2160 at 120 Hz remains stable. Then test 144 Hz with VRR still off, add VRR, and add HDR last. The first transition that produces a black screen identifies the failing layer: fixed 144 Hz points toward the high-rate timing, cable, port, or driver; stable fixed 144 Hz but unstable VRR points toward variable-refresh behavior; HDR-only failures point toward format or bit-depth negotiation.

LG specifies C4 VRR up to 144 Hz for compatible PC/game inputs; consoles should be tested at their supported 120 Hz mode. A short pause during a deliberate resolution, HDR, or refresh switch can be HDMI resynchronization. Repeated flashes, “No Signal,” corruption, or failure to recover are not normal.

Symptoms: Separate Three Different Problems

Record whether audio continues and whether the C4 reports “No Signal.” Use one repeatable desktop workload and one game; do not mix results from random loading screens.

Instant blackout when selecting 144 Hz: the 144 Hz mode is not completing negotiation.

Image returns every few seconds: the link repeatedly loses and reacquires synchronization.

Near-black brightness pulsing without “No Signal”: this can be OLED VRR gamma flicker rather than a dropped HDMI signal.

Black screen only on Alt-Tab or game exit: exclusive-fullscreen mode is switching timing, HDR, or VRR state.

Artifacts or green flashes before loss: cable integrity, output format, GPU stability, or port contact deserves priority.

TV menus and sound remain responsive over a black input: the source path has failed; the panel has not necessarily shut down.

Owners report FreeSync-linked flicker at 144 Hz and black screens after leaving exclusive fullscreen. These reports prove symptoms, not one universal defect.

Causes and 120/144 Hz Diagnostic Tree

Branch 1: Is fixed 120 Hz stable?

In Windows Advanced display, select the C4 and verify 3840 × 2160, 120 Hz, SDR, and VRR off. Confirm the active signal mode, not only the desktop mode. Run the same workload long enough to cover the normal failure interval.

If 120 Hz also fails, reduce to 60 Hz, change the direct cable, try another input, and inspect the driver. Stable 120 Hz becomes the baseline for every following comparison.

Branch 2: Does fixed 144 Hz fail with VRR and HDR off?

Enable the C4's 144 Hz mode for the PC input and choose 144 Hz in Windows, while leaving VRR and HDR disabled. If the screen fails immediately, wait for Windows' automatic settings rollback rather than pulling power. Try the other refresh-rate entry if the driver exposes 143.98 and 144.00 Hz, but do not create undocumented custom timings.

A fixed-refresh failure implicates the high-rate path rather than changing game fps. Update the driver, test a practical-length certified cable and another C4 port. Remove receivers, switches, capture cards, couplers, and adapters.

Branch 3: Is 144 Hz stable until VRR is enabled?

Enable only one VRR implementation at a time. On AMD, confirm FreeSync in both Game Optimizer and AMD Software; AMD documents the global and per-application controls. On NVIDIA, use the G-SYNC-compatible controls supported by the connected display. Avoid simultaneously changing frame caps, V-Sync, Enhanced Sync, HDR, and low-latency settings.

If VRR alone causes loss, cap the game below the upper boundary—for example, 138 to 141 fps—and compare borderless with exclusive fullscreen. Near-black pulsing while the signal remains present is more consistent with VRR luminance flicker. Stabilize frame rate or disable VRR for that title.

Branch 4: Does HDR trigger the dropout?

With fixed 144 Hz confirmed, turn on Windows HDR but keep VRR off. HDR commonly changes bit depth and signaling. If that single change breaks the link, compare 10-bit and 8-bit output where the GPU permits, then retest 120 Hz HDR. Stable 120 Hz HDR and unstable 144 Hz HDR points to the higher combined format demand, not HDR content itself.

HDMI data demand changes with resolution, refresh, chroma, and depth. A cable passing 4K120 may lack margin for another format. Verify its certification label, not seller claims.

Branch 5: Does failure occur only when modes change?

Set the desktop and game to the same resolution, refresh rate, and HDR state. Prefer borderless windowed for one trial. If black screens disappear, the trigger is the transition rather than sustained 144 Hz. Disable automatic HDR switching or configure the game to match the desktop. A single brief resync can remain, but the image should recover without unplugging the TV.

If exclusive-fullscreen exit leaves the C4 black while 120 Hz recovers, report the exact sequence and firmware versions to LG and the GPU vendor.

Step-by-Step Safe Fix

Document versions and modes. Photograph C4 Game Optimizer status and Windows Advanced display; note GPU model, driver, active signal, bit depth, HDR, and VRR.

Remove intermediaries. Connect GPU HDMI directly to the C4 with a certified Ultra High Speed cable shorter than the problematic run where practical.

Prove 4K120 SDR fixed refresh. Test long enough to be credible. If it fails, solve that general link issue first.

Test 4K144 SDR fixed refresh. Change no other feature. Try another C4 HDMI port and one known-good certified cable if it fails.

Add VRR alone. Enable the matching AMD or NVIDIA control, then use a frame cap below 144 and compare borderless versus exclusive fullscreen.

Add HDR last. Confirm the resulting bit depth and color format. Return to 120 Hz HDR if 144 Hz HDR becomes unstable.

Update deliberately. Install official C4 firmware and a current stable GPU driver. If the issue began immediately after a driver update, use the vendor's supported rollback path and record both versions.

Restart once after changing the physical chain. Repeatedly unplugging only forces renegotiation. Preserve the test matrix before any reset.

Cautions and When to Use 120 Hz

Do not edit EDID blocks, increase HDMI voltage, flash unofficial TV firmware, or enter the service menu. Avoid custom 144-Hz timings unless the GPU vendor or LG explicitly asks for them. Pixel cleaning and OLED protection settings cannot repair an HDMI dropout.

Using stable 4K120 is a valid workaround while a 144-Hz-specific driver or link fault is investigated. The difference is modest compared with losing frames to blackouts, and consoles should remain at their supported mode. Keep 144 Hz disabled for movie devices and receivers that do not advertise it.

Contact LG if the same certified direct cable and two capable PCs fail at fixed 144 Hz on multiple C4 inputs with current firmware while 120 Hz remains stable. Contact the GPU vendor if the fault follows one graphics card or driver across displays. Stop testing and arrange service if ports are loose, hot, or show corruption without a mode change.