Diagnosis
This is expected behavior due to the Multi-Monitor Sync (MMS) feature in Dell Display Manager (DDM). When MMS is active, it synchronizes the primary monitor's settings—like brightness and color—across all daisy-chained monitors to create a uniform image. Consequently, DDM's individual control panel is disabled for the second and any subsequent monitors in the chain. Only the first, or "master," monitor can be directly adjusted via the software interface when MMS is ON.
How to Fix It
To control each monitor's brightness independently, you must disable Multi-Monitor Sync.
- Open the Dell Display Manager application on your computer.
- Navigate to the "Multi-Monitor Sync" or "MMS" section, typically found in the main settings or control panel.
- Toggle the Multi-Monitor Sync function to OFF.
- Once disabled, DDM should detect each monitor separately. You can then use the software to adjust the brightness and other settings for your second (daisy-chained) monitor individually.
If That Didn't Work
Ensure your monitor chain is correctly set up. Verify the DisplayPort cables are firmly connected and support DisplayPort 1.2 or later (required for daisy-chaining). If the issue persists, try closing and reopening Dell Display Manager, or restart your computer. As a direct workaround, you can always adjust the brightness of the second monitor using its physical On-Screen Display (OSD) buttons, regardless of DDM's settings.
Heads Up
Disabling MMS means you will need to calibrate brightness and color settings on each monitor manually to achieve visual consistency across your setup.