After reading this thread
It looks as though the tftp recovery can use different IP addresses to the default once openwrt is flashed. It won't respond to ping either.
Can you try the following
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Make sure your AP is powered on, and has one available ethernet port.
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Press and hold the Reset button. Do not release it until step 4.
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While continuing to press the Reset button, connect your computer to the available ethernet port of the AP.
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Continue holding the Reset button until the light begins flashing white > blue > off as indicated in our LED Status Guide. This indicates your device is ready for TFTP Recovery and you can release the button.
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Set a static IP address on your computer to communicate with the AP
Static IP: 192.168.1.25
Subnet: 255.255.255.0
- Run nmap to determine the routers IP address
sudo nmap -sn 192.168.1.*
- Send firmware using tftp to the discovered IP address
Can you post the output of nmap please? Hopefully you can see the host during the scan!