Causes
- Connected over HDMI instead of DisplayPort — the S27AG55 has one DisplayPort 1.2 and two HDMI 2.0 inputs. HDMI 2.0 does not have the bandwidth for 2560x1440 at 165Hz with 8-bit RGB, so 144Hz is the ceiling on either HDMI port no matter what the PC offers. This is the single most common reason the 165Hz option never appears.
- The monitor's own Refresh Rate setting is still at 144Hz — this model has a Refresh Rate option in the OSD that caps the link independently of Windows. Units ship at 144Hz or lower, and until that value is raised the operating system cannot select 165Hz even on DisplayPort.
- Windows is still driving the panel at 60Hz or 144Hz — Windows defaults a newly detected display to a safe mode and keeps it there. Plugging in the G5 and expecting 165Hz without touching Advanced display leaves the desktop at 60Hz, which is why the monitor feels slow even though the hardware is capable.
- 10-bit color selected on a DisplayPort 1.2 link — HBR2 has just enough bandwidth for 1440p at 165Hz in 8-bit, but switching the output to 10 bpc pushes the required data rate past the link and the driver silently falls back to 144Hz or 120Hz. The refresh-rate list then shows 165Hz as unavailable and the cause is the color-depth setting, not the cable.
- An adapter, dock, KVM, or second display in the chain — HDMI-to-DisplayPort adapters, USB-C docks, and KVMs commonly negotiate HBR (DisplayPort 1.1) rates only, capping 1440p at 60–120Hz. Cloning the desktop to a 60Hz laptop panel or TV forces both displays to 60Hz in the same way.
- Source device limits — a PlayStation 5 or Xbox caps 1440p at 120Hz over HDMI 2.0, and some laptops only expose 165Hz through a specific USB-C or mini-DP port wired to the discrete GPU. If the source cannot output it, no monitor setting will help.
How to Fix
- Use the DisplayPort input with a DisplayPort 1.2 cable — plug the supplied DP cable, or another certified DP 1.2 (HBR2) cable, into the monitor's single DisplayPort input and directly into the graphics card. Skip HDMI, skip adapters, and skip docks or KVM switches while testing.
- Raise Refresh Rate in the monitor OSD — press the joystick under the bottom-right of the bezel, open System → Refresh Rate, and set it to 165Hz. Confirm the input source shown in the OSD is DisplayPort at the same time, because the option is limited to what the active input can carry.
- Select 165Hz in Windows — open Settings → System → Display → Advanced display, pick the Odyssey G5 in the display dropdown, set the resolution to 2560 x 1440, then set Choose a refresh rate to 165Hz. If only 60Hz and 144Hz are listed here, the OSD or cable step above has not taken effect yet.
- Set it again in the GPU control panel — in NVIDIA Control Panel → Change resolution select the G5, confirm 2560x1440, set Refresh rate to 165Hz, and apply; on AMD open Adrenalin → Display and set the refresh rate there. Applying it in both places prevents Windows from reverting after a reboot.
- Set color depth to 8 bpc — in NVIDIA Control Panel choose Use NVIDIA color settings and set Output color depth to 8 bpc (RGB, Full), apply, then reopen the refresh-rate list. On AMD, use Color Depth 8-bit in the display settings. This frees the bandwidth that 10-bit was consuming on DisplayPort 1.2.
- Stop mirroring another display — in Windows Display settings set the G5 to Extend and make it the only active display while testing. A cloned 60Hz panel or TV drags the G5 down to the same rate.
- Update the GPU driver and retest — install the latest driver from NVIDIA, AMD, or Intel, reboot, and check Advanced display again. Older drivers can fail to expose 165Hz on DP 1.2 panels even when the hardware supports it.
- Confirm the limit is the monitor, not the PC — test the G5 on a different computer or GPU with the same DP cable. If 165Hz still does not appear on DisplayPort at 8-bit with FreeSync on or off, the scaler or firmware is at fault and the unit should go back to Samsung under warranty.
