While V9.0 is highly recommended for its stability, users must exercise caution:
By: Network Engineering Desk
If you are reading this, you are likely one of the thousands of users or ISPs (Internet Service Providers) struggling with a specific hardware revision of a popular GPON ONT: the ZTE F670L V90. The internet forums are flooded with a single desperate question: "How do I fix the top issue?" zte f670l v90 firmware fixed top
In the world of fiber optic networking, the term "Fixed Top" has become a colloquial shorthand among technicians for a specific build of the ZTE F670L V90 firmware that resolves the dreaded CPU spiking to 100% (hitting the "top") and the subsequent connection drops.
This article dives deep into what the "Fixed Top" firmware is, the symptoms it cures, how to identify your current firmware version, and the step-by-step process to safely upgrade your device. While V9
Even with the “fixed top” firmware, some users report edge cases. Here’s a troubleshooting table:
| Issue | Likely Cause | Solution |
|-------|--------------|----------|
| Web interface still slow after upgrade | Browser cache | Clear cache or use incognito mode. |
| Wi-Fi 5 GHz disappears after a few hours | DFS channel conflict | Force a non-DFS channel (e.g., 36, 40, 44). |
| Cannot access 192.168.1.1 after upgrade | IP conflict with ISP modem | Disconnect fiber, reboot, change LAN IP to 192.168.2.1. |
| VoIP no longer registers | SIP port mismatch | Re-enter SIP server details from ISP. |
| USB drive not recognized | Format incompatibility | Reformat drive as FAT32 or NTFS (not exFAT). | Even with the correct "Fixed Top" file, things can go wrong
If all else fails, re-flash the firmware or contact your ISP for an official config file.
Even with the correct "Fixed Top" file, things can go wrong.
| Error | Solution |
| :--- | :--- |
| "Integrity check failed" | The file is corrupted or for a different HW revision (V86 vs V90). Redownload. |
| ONT stuck on PON light flashing after reboot | The OMCI version changed. Call your ISP to re-provision the ONT. |
| Wi-Fi shows "No Internet" | Perform a 30-30-30 reset (Hold reset for 30 seconds while powered, unplug for 30 seconds while holding, plug back in for 30 seconds). |
| GUI password changed | The fixed firmware likely reverted to default admin / admin or user / ZTE521. |
A: Indirectly, yes. The “fixed top” patch stops the 5 GHz radio from dropping, which improves perceived range. However, transmit power remains the same as hardware allows (around 20 dBm).