☐ Avoid USB 3.0 ports (blue inside). Use USB 2.0 (black/grey). USB 3.0 emits radio noise that kills Bluetooth 2.4GHz signals. ☐ USB Extension cable: If the dongle is plugged into the back of a metal tower PC, use a short USB 2.0 extension cable to bring the adapter into open air. This doubles range. ☐ Disable onboard Bluetooth: If your laptop has built-in Bluetooth, disable it in BIOS or Device Manager. Two active Bluetooth radios will conflict. ☐ Run the official UGREEN tool (Method 4) even if Windows says the driver is installed. It cleans orphaned registry keys. ☐ Restart, don't shut down. Windows Fast Startup often prevents Bluetooth drivers from loading correctly. After install, do a full Restart (not Shutdown + Power on).
The CM390 is too small to come with a CD. If you lost the manual, scan the QR code on the back of the plastic packaging. It usually links directly to: driver.ugreen.com (Search for "CM390"). ugreen bluetooth 50 usb adapter cm390 driver install
The installation method differs slightly between Windows 10 and Windows 11. ☐ Avoid USB 3