Major monitor is flickering when using kvm switch and thunderbolt4 docking station.

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suptest Author

Level 1

4 points

Major monitor is flickering when using kvm switch and thunderbolt4 docking station.

Hi,

I'm experiencing an issue with my current setup:

Equipment:

KVM Switch: Navceker KVM (DP + HDMI, supports 8K at 60Hz)
Thunderbolt 4 Docking Station: Orico TB4 Dock (12-in-1)
Computers: Windows Desktop and MacBook M3 Max 14"
Monitors: Main (LG 32GP83B) and Sub (Samsung 27" FHD)

Connections:

Macbook ─tb4─ TB4 dock ─dp, hdmi, usb─┐ ┌─dp─ main monitor

┣── kvm ──┫

Desktop ─dp, hdmi, usb─┘ └─hdmi─ sub monitor

Issue: When all devices are connected simultaneously, the main monitor repeatedly connects and disconnects every second.

Troubleshooting Attempts:

Tested the setup with a Windows laptop instead of the MacBook; it worked fine.
Connected the MacBook directly to the monitors, bypassing the KVM switch and docking station; it worked fine.
Connected the Macbook only with KVM Switch or docking station; it worked fine.
Replaced all cables with high-quality alternatives; the issue persisted.
Updated macOS from version 14.6 to 15; no improvement.
Change the Main monitor to mirror mode or fix the refresh rate; macbook built-in monitor also start to flickering.
Connect only with sub monitor; it worked fine.

The problem occurs only with the main monitor connected via the DP cable.

I'm seeking assistance to identify and resolve this frustrating issue. Any insights would be greatly appreciated.

Thanks.

MacBook Pro 14″, macOS 15.1

Posted on Dec 12, 2024 8:42 PM

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Answer 1

Dec 13, 2024 11:12 AM in response to suptest

Modern displays are operating near the limits of switching speeds for the type of logic used. In order to avoid signal degradation, cable lengths from transmitter to receiver in each same-technology section of the cable must be kept appropriately short.

for DisplayPort and USB cables, that length is about one meter. So if your KVM is NOT ACTIVE, i.e., just a passive switch and NOT a re-Driver, the sum of the cable length is limited to one meter.

for Thunderbolt-3 and -4 , the length is limited to 0.5 meters in most cases.

HDMI has two cases. Above 4K at 60, the switching technology changes, and although the HDMI authority has not published length guidelines that I know of, those higher speeds are similar to DisplayPort signals, and should consider honoring the one-meter length.

HDMI up to 4K at 60 is not strongly length limited.

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