Causes
- VRR luminance flicker while FreeSync / G-Sync Compatible is active — the S27AG55 is a 3000:1 VA panel rated 48–165Hz for variable refresh. As the frame rate drops toward the bottom of that range, or spikes between two values, the panel's brightness tracks it and the whole image visibly pulses. Menus, loading screens, and open-world games that swing between 60 and 160 fps are the classic trigger, and toggling FreeSync off is the fastest way to confirm it.
- Response Time set to Extreme or Faster — the overdrive levels on this VA panel are aggressive at 165Hz. Extreme pushes pixel transitions past their target, and the resulting overshoot reads as bright flashes and shimmer on moving edges, especially on dark scenes where the panel already transitions slowly.
- HDR switched on for SDR content — the Odyssey G5 is DisplayHDR 400 with no local dimming, so HDR is produced entirely by pushing the edge backlight. With HDR left enabled on the desktop, the backlight oscillates between near-identical brightness steps and the screen pulses, a pattern that is most obvious in browsers and file explorers rather than in games.
- A marginal DisplayPort 1.2 link at 165Hz — 2560x1440 at 165Hz is close to what DisplayPort HBR2 can carry. A long, thin, or adapter-patched cable, or a connector that is not fully latched, causes the link to retrain and produces single black frames or a sharp bright flash rather than the slow pulsing of VRR flicker.
- An outdated GPU driver or a driver-level VRR mismatch — G-Sync Compatible on a FreeSync-only monitor depends on the NVIDIA driver's VRR handshake. Driver updates that change that path, and Windows updates that reset the display to a different refresh rate, both bring back flicker that was previously gone.
How to Fix
- Prove whether VRR is the cause — open the OSD with the joystick under the bottom-right of the bezel, go to System → FreeSync and set it to Off. On NVIDIA also open NVIDIA Control Panel → Set up G-SYNC and clear Enable G-SYNC, G-SYNC Compatible. If the flicker stops immediately, everything below is about keeping VRR usable; if it continues with VRR off, skip to the cable steps.
- Cap the frame rate inside the refresh range — in each game set a limit of about 160 fps at 165Hz (or 140 fps at 144Hz) instead of Unlimited, and turn on NVIDIA Max Frame Rate or AMD Radeon Chill at the driver level. A stable frame rate that never dips below roughly 60 fps removes most luminance swing. Avoid leaving menus and loading screens at uncapped frame rates where the rate collapses and recovers constantly.
- Set Response Time to Standard — in the OSD open Picture → Response Time and choose Standard. Standard is the only level on this panel that does not add visible overshoot; Faster and Extreme trade smear for bright edge flashes that look like flicker during fast motion.
- Turn HDR off for desktop use — go to Windows Settings → System → Display → HDR and switch HDR off for everyday work, enabling it only for HDR games and video. With HDR off, set brightness around 35–45 in the OSD so the edge backlight is not running at full output on a white page.
- Reseat and replace the DisplayPort cable — power down the PC and monitor, unplug the DP cable at both ends, check for bent pins, and re-seat it until it latches. Use the cable in the box or another certified DisplayPort 1.2 cable no longer than 2m, plugged straight into the graphics card rather than through a dock, KVM, or adapter. If the flicker is a single black frame every few minutes, this is usually the whole fix.
- Drop to 144Hz to test the link — in Settings → System → Display → Advanced display set the S27AG55 to 144Hz and play for a session. If 144Hz is clean and 165Hz flickers, the panel or scaler cannot hold the higher timing on your sample and 144Hz is the practical setting until it is serviced.
- Clean-install the GPU driver — download the latest driver from NVIDIA, AMD, or Intel, then if the problem persists remove the old one with Display Driver Uninstaller in Safe Mode and reinstall. After the install, re-check the refresh rate and re-enable FreeSync only if you want VRR back.
- Test a second source before assuming the panel is faulty — connect a laptop or console on a different cable and input. Flicker that follows the monitor across two sources on two cables, with FreeSync off and HDR off, is a backlight or scaler fault, which is a warranty repair from Samsung rather than a setting.
