Troubleshooting
Find your symptom, then follow the first check. Many problems turn out to be a documented limit or a setting, so diagnose before you replace hardware.
| Symptom | Likely explanation to rule out first | Go to |
|---|---|---|
| Only one of two monitors works | Your Mac's native limit (M1, M2, or M3 with the lid open) | Diagnostic guide, Q1 and Q2 |
| Both monitors show the same picture | Mirroring setting, or an MST dock on macOS | Diagnostic guide, Q3 |
| M3 Air: second monitor goes dark when you open the lid | Documented Apple behavior | M3 lid-state guide |
| A monitor is missing after sleep or startup | Monitor auto input detection | Diagnostic guide, wake branch |
| DisplayLink screens blank until login | DisplayLink Manager starts after login | Native video vs DisplayLink |
| Streaming video won't play with a DisplayLink screen attached | Protected video is not supported on DisplayLink screens | Native video vs DisplayLink |
| Monitor stuck at 30Hz or low resolution | A cable or adapter in the path not rated for the mode | Cable guide, dual 4K checklist |
| Laptop charges slowly or not at all | Host-port wattage, port or cable without charging, charging limit setting | Charging guide |
Before you change anything
Write down your Mac model and chip, macOS version, lid state, dock model, each monitor model and input, and every cable. The dock maker's support will ask for the same list.
What we never suggest
- Disabling macOS security features or accessory approval.
- Deleting system or preference files.
- Buying a replacement before a direct-connection test shows which part fails.