PG27UCDM - USB C Display Port not working

[lordozivert]

I recently picked up the PG27UCDM and updated it to the latest firmware (MCM105). My setup is pretty straightforward: the PG27UCDM and my second monitor (AW3418DW) are both connected to my GPU via DisplayPort. My keyboard, mouse, and an external USB hub are connected through the monitor’s built-in KVM. Everything on that side works perfectly.

The issue is with the USB-C DisplayPort connection. When I try to connect my laptop (UX6404), the monitor just shows USB-C NO SIGNAL and immediately switches back to the main DisplayPort input. I’ve tried another USB-C cable—same result. The laptop itself works fine when I plug it into my work setup using USB-C, so I’m not sure why the PG27UCDM won’t pick it up.

Additional details that might help:

• ⁠HDMI 2.1 ports are currently used by my PS5 and Switch
• ⁠Auto Input Detection: ON
• ⁠Auto KVM Detection: ON
• ⁠USB Setup > KVM > USB-C > KVM (USB-C) → KBM works, but no video signal when switching to USB-C
• ⁠USB Setup > KVM > USB-C > KVM (USB-B) → KBM works, but still no video signal
• ⁠USB Setup > KVM > DisplayPort > KVM (USB-C) → lose KBM entirely
• ⁠USB Setup > KVM > DisplayPort > KVM (USB-B) → KBM works, but still no USB-C signal
• ⁠USB Setup > Type-C Bandwidth (USB 2.0 / USB 3.2) → no change
• ⁠USB Hub: On During Standby
• ⁠Power Setting > Performance Mode: ON
• ⁠DisplayPort Stream set to DP 2.1, also tried 1.4, no difference
• ⁠USB-C Charging fluctuates between 17–20W (this I find very weird, its a 240W cable and the monitor is said to be able to offload 90W)

[Aureliannn_ROG]

Hi @lordozivert  ,

to help us narrow down the cause of this “Unknown USB device” pop-up, could you help confirm a few details:

1. Does the pop-up appear only when the PG27UCDM is connected through USB-C?
   If you disconnect the monitor’s USB-C cable, does the notification disappear completely?
2. Are you using the original ASUS USB-C cable that came with the monitor?
   If possible, please try another USB-C → USB-C cable (full-featured cable with power + data) to compare.
3. When the monitor is connected, is the USB hub function enabled?
   (Please check: System Setup → USB Hub → Enable/Disable)
   If USB Hub is disabled, does the pop-up still occur?
4. Any USB devices connected to the monitor’s downstream USB ports?
   For example: webcam, headset, dongle, keyboard.
   If yes, please test with nothing plugged in.
5. Does the issue occur when HDR, OLED Care, or Aura Sync is turned off?
   We want to check whether it is related to the monitor’s internal USB interface.
6. Laptop information: Windows version/ NB USB drivers / Thunderbolt driver version/ Whether UX6404 Vantage or Thunderbolt Control Center shows any notification during the pop-up
7. Monitor serial number (via PM box)

Once we have the above information, we'll pass to the team for further verification.

Thank you.

[phoqu3]

I'm experiencing the exact same issues on my XG32UCWMG. 

Everything connected through the hub (keyboard + mouse) is running perfectly through the USB-A --> USB-B cable connected to my main pc (using a DisplayPort cable too).

Whenever i try to connect my laptop via USB-C, nothing works - neither the keyboard/mouse nor any display. 

When i connect the USB-C cable to my laptop i will briefly get a notification about a new HDR-compatible device, but i cannot detect the monitor in any way. 

Updating the firmware of the monitor didnt help either - i have tried different USB-C to USB-C cables without luck (all capable of 10 gbps). 

I specifically got this monitor due to the KVM functionality.....