A firmware change can leave old configurations (VLANs, PPPoE credentials, TR-069 settings) corrupted.

Open a web browser and enter your router's IP address (typically 192.168.1.1 or 192.168.0.1 ). Log in with your admin credentials .

Assuming you have obtained the firmware file (named something like ZTE_F680_V6.0.0P12T23.bin ), follow these exact steps.

Log back in. Do not restore your old backup file (that may re-introduce bugs). Instead, manually reconfigure:

Without the correct LOID or Serial Number, the F680 will show “PON blinking” and never go online.