Question 1

Install fails or rolls back?

Accepted Answer

Disconnect the MF691 USB modem, close any T-Mobile webConnect/DC Control software, then run the installer as administrator. Temporarily disable antivirus and allow any legacy/unsigned driver prompt. Reboot before reconnecting the device.

Question 2

Device not detected?

Accepted Answer

Use a direct rear USB port, not a hub. Check Device Manager for an unknown modem or COM port. Reinstall the driver and connect the MF691 only when prompted; verify the SIM and USB connection are seated.

Question 3

Version conflicts?

Accepted Answer

Uninstall older T-Mobile webConnect/DC Control and previous modem drivers via Programs and Features and Device Manager, including hidden devices. Reboot, then install one matching MF691 driver package. Avoid mixing Windows Update and vendor drivers.

T Mobile MF691 webConnect DC Control Driver