I'm new in OpenWrt and I have a problem with UniElec U7628-01 (tech data unielec_u7628-01).
I have tried to install the last release of OpenWrt firmware (19.07.3) using the LuCI interface and this upgrade guide. I have uploaded through the LuCI interface the u7628-01-128M-16M-squashfs-sysupgrade.bin firmware upgrade file taken from this resource.
But something went wrong because now I can no longer use the router. I supposed that during the upload I lost the wi-fi connection with the router (yes, I know, I should have used the ethernet cable), but I'm not sure if this is the cause. Now I can no longer use the LuCI interface, I can't establish an ssh connection, the wi-fi access point doesn't work anymore and the ethernet doesn't establish an IP configuration. When I turn the platform on, the Wi-Fi led stays on for only a few seconds and then turns off, while before when the access point worked, that led flashed. I have tried to reset and access the recovery mode as explained in Since Supported Commit and I have tried a TFTP connection with ethernet, but nothing.
The only thing I haven't tried is a serial connection because I don't have the USB adapter.
What should I do? Is it possible that an error during the upgrade has done so much damage? What happened?
There is not much information about the UniElec U7628-01 and I can't understand which is the way to resolve this problem. I thought that the current firmware is corrupted and that I should flash a new firmware but if I can't access the router with a TFTP connection though an ethernet cable, how can I flash a new firmware? Can I flash a new firmware with a serial?
Thanks in advance