I have one of the early versions of AR300M.
It was used for a long time, but i needed to upgrade to install vxlan.
The upgrade failed in horrible ways and uboot was also refusing to install images (this is the old uboot that have the mtu issues and refuses to accept images as a result).
I resorted to soldering on the uart connectors and on the serial now I see:
it does not seem to accept any input from me however.
When disassembling the unit the reset button came off it seems.
Everything I have read assumes that the serial works which does not seem to work for me.
I have hardware and software flow control off with 115200 8N1.
You can try to upgrade the uboot version first and then install the new firmware.
If the reset button is damaged, the another way to uboot is only connected through the serial port.
After the device is powered on, immediately press gl or j to abort the bootloader startup, and then enter the command httpd to activate the uboot web UI:
Unfortunately this had a really old uboot with the bug which prevented upgrades. After a lot of trying and connecting multiple serial ports I ended up with a working setup.
(I was not clear to me why it started working, but it seems persistence was an important factor because it was not deterministic and even after a reboot the serial was either working or not at times.)
I was able to install a new uboot by issuing the commands documented in the debrick manual.
The second challenge was getting the NAND storage up and running. For that it seems uploading the openwrt nand factory image (via uboot serial again) was the winning strategy.
