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Fix Guide

How to Fix USB4 DisplayPort Alt Mode Not Working on the Minisforum UM890 Pro

Device: Minisforum UM890 Pro · Minisforum Added

Causes

  • The UM890 Pro's USB4 ports use a multi-function USB4 controller that shares DisplayPort lanes with the integrated Radeon 780M iGPU's display outputs (HDMI 2.1 and DisplayPort 1.4) — when a monitor is connected to both a USB4 port and the native HDMI/DP port simultaneously, the iGPU's internal display pipeline routing can fail to assign DP Alt Mode bandwidth to the USB4 port, leaving the connected monitor blank or undetected
  • Many USB-C to HDMI or USB-C to DisplayPort cables and adapters are not rated for full USB4 40 Gbps DP Alt Mode throughput — passive adapters that only support USB 3.2 Gen2 (10 Gbps) or DisplayPort 1.2 (HBR2) cannot negotiate the higher HBR3 link rate required for 4K at 120 Hz or 5K+ resolutions, causing the display to flicker, show no signal, or default to a low resolution like 640×480
  • The UM890 Pro's BIOS pre-allocates PCIe lanes for the USB4 controller using a specific lane budget — if the M.2 slots or OCuLink port are populated with high-bandwidth devices, the USB4 controller may not receive enough PCIe lanes to enable DP Alt Mode, resulting in the USB4 ports functioning for data but failing to output any video signal
  • Outdated Thunderbolt/USB4 controller firmware (the ASMedia ASM2464PD or similar USB4 controller used on the UM890 Pro) can have bugs in the DP Alt Mode handshake that prevent monitors from being detected, particularly with USB-C hubs or docks that use DisplayPort Multi-Stream Transport (MST) for dual-monitor setups
  • The Radeon 780M iGPU's display driver may prioritize the native HDMI 2.1 and DisplayPort 1.4 outputs over the USB4 DP Alt Mode path in the display adapter's output routing table, leaving the USB4 video output in a disabled or standby state until the native ports are explicitly disabled

How to Fix

  1. Test with a known-good USB4-certified or Thunderbolt 4 cable that explicitly supports DisplayPort Alt Mode at 40 Gbps. Avoid USB-C cables that only list USB 3.2 Gen2 (10 Gbps) support — these lack the additional high-speed lanes needed for DP Alt Mode. The UM890 Pro's USB4 ports require a full-featured USB4 cable with all four PCIe lanes wired for DisplayPort
  2. Connect the monitor to the USB4 port before powering on the UM890 Pro. Many USB4 controllers only negotiate DP Alt Mode during the initial PCIe enumeration at boot time. If you connect the display after Windows has loaded, press Win + Ctrl + Shift + B to reset the graphics driver, which forces the iGPU to re-enumerate all connected displays including the USB4 DP Alt Mode path
  3. Enter the BIOS by pressing Del during startup. Navigate to Advanced → AMD PBS → USB4 Configuration. Ensure USB4 Controller is set to Enabled and DP Alt Mode is set to Enabled (not Auto). Also check that PCIe ASPM Support is set to Disabled — active-state power management can interfere with the DP Alt Mode link training on some UM890 Pro BIOS versions
  4. Disconnect any monitors from the native HDMI 2.1 and DisplayPort 1.4 ports, leaving only the USB4 monitor connected. Reboot the UM890 Pro. With the native ports empty, the iGPU's display routing logic has no choice but to route a display pipeline through the USB4 DP Alt Mode output. Once the USB4 display is working, you can reconnect the other monitors one at a time, restarting between each addition
  5. Update the USB4 controller firmware: go to the Minisforum UM890 Pro support page and download the latest USB4/Thunderbolt firmware update tool. Run it as Administrator and follow the on-screen instructions. The firmware update fixes known DP Alt Mode handshake issues on the ASMedia controller. After the update, shut down (not restart) the UM890 Pro, disconnect AC power for 30 seconds, then boot up with the USB4 display connected
  6. If using a USB-C hub or docking station, test with the monitor connected directly to the UM890 Pro's USB4 port, bypassing the hub. Many USB-C hubs do not correctly implement the DisplayPort Alt Mode tunneling required by USB4, especially MST hubs that split a single DP stream into multiple outputs. If the direct connection works, the hub is the problem — look for a hub specifically certified for USB4 with DP Alt Mode
  7. In AMD Software: Adrenalin Edition, go to Display tab and look for the USB4-connected display in the display list. If it shows as a detected but disabled display, click the multi-display settings and force-enable it. If it does not appear at all, click the Additional Settings gear icon → Display → Force Display Detection to trigger a fresh EDID handshake over the USB4 link
  8. As a last resort, open Device Manager and expand Universal Serial Bus Controllers. Find the USB4 Host Router or ASMedia USB4 Controller device. Right-click it → Uninstall Device (check "Attempt to remove the driver for this device"). Restart the UM890 Pro. Windows will reinstall the USB4 controller driver fresh, which often resolves DP Alt Mode routing conflicts caused by corrupted driver state