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My super old Archer 1600v TPG modem is back to rebooting itself after a minute or two, to repeat the process.
I've experienced this twice in the past, powering it off on, or holding the reset button does not fix it.
This post is more to help others in the same situation, after attempting the above.
The fix is to login to the modem(192.168.1.1) before it reboots again, and click on 'factory restore' within the console, the telephone line also needs to be connected(!).
Advance > System Tools > Reboot > tap 'factory restore'
Wait for it to reboot & configure.
I had previously held the physical reset button for 10 ro 15seconds in an attempt to fix it. I believe this action wiped my previous personal preferred settings.
Username & Password reverted to admin admin.
You can update this login via Advance > System Tools > Account Management > Old username / password ... New Username / password > Save.
Wifi name & password can be changed back to previous via Advance > Wireless > Wireless settings > Wireless Name / password > Save. Click on '5GHz' to update also. Same Wifi name & password can be used.