I tried to flash 19.07.5 on this device some years ago. I posted a thread here to make sure it was safe first. Unfortunately there was a problem with 19.07.5 Openwrt and this device but this was not mentioned in the Wiki page until later, and then it was too late
The wiki page says this:
Beware: ath79 Image for the TL-WR810N v1.1 (EU) is currently broken and will result in a soft-bricked device. Use the ar71xx image (http://downloads.openwrt.org/releases/19.07.7/targets/ar71xx/generic/) instead! See thread: TP-Link TL-WR810N v1 - ath79. Update: OpenWRT 19.07.7 ath79 now does not result in a boot-loop on this device, but USB will not provide power. Snapshots from 27.2.2021 onward have USB-power-issue fixed, 21.02-rc2 should also have it fixed, see: ?p=openwrt/openwrt.git;a=commitdiff;h=62099d98e4746d8a4e9ee79360314c1900c8974e.
Recovery after this soft-brick may be possible via the tftpd method (see below).
The result of my flashing is that the device will turn on but the LAN connection is only on very short time, not long enough to connect or get SSH connected. The blue LED on the device flashes on and off very slowly. This continues until device is switched off. Is this soft-brick?
I can't use the TFTP method from wiki, and it says the only solution now is serial console. Is this correct for my case?
If I have to use serial console I will have to learn to solder and to buy the tools, but this is all OK, good time to learn But the wiki has I think an error in the text here:
This test point is not directly connected to the SoC, next to it is an unpopulated jumper (R107) that needs to be closed. This can easily be done by soldering not the end of a piece of enamelled wire to the test point, but letting about 1mm of wire stand out of the solder joint over the pads of the jumper, and then pulling solder from the solder joint over the jumper.
Is this bold word "not" correct? The sentence doesn't make sense to me like this. Also if someone wants to provide another description I can use this too - more information is better so I can save this device.
Given the system specs, this would not be economically sensible - you'd get better devices for less money on the second hand markets, than soldering equipment would cost you.
Probably. TP-Link likes to cut the rx traces, so in addition to making a steady connection to three points, you might have to bridge a missing 0-ohm resistor to fix the connection. soldering is the easiest/ most reliable approach to accomplish that, but you may also have luck with just pressing cables/ pins at the right places. You'll only know once you have tried it.
Be aware that if push-button tftp (really) fails, chances for serial recovery aren't that stellar either - as this still requires the bootloader to remain functional (and the wifi calibration data to remain untouched, if you want to use your wifi again), but if it were functional, the push-button tftp recovery procedure implemented in the bootloader should have already worked. Your only chance for success via serial console would be having a too old bootloader, which doesn't implement push-button tftp recovery - TP-Link may have retrofitted it later during their upgrade cycle.
Plainly said, if you already own a usb2serial adapter and the necessary soldering equipment, knock yourself out - all you have to lose is wasting a couple of hours.
But if this is your first rodeo, the money is better spent on a new (second hand?) device that just works and provide better system specs.
My first advice would be to spend a little more time on getting the push-button tftp recovery to work, respectively to check on the wire (wireshark/ tcpdump) how far that goes, no harm done trying it a few times more, beyond that... see above.
Yes, I don't have the tools. But I thought of buying them in one way anyway so this is just a good time for it. Your advice is good about TFTP though. You say that if this is not working then serial console is perhaps not also going to work anyway. So, I will try TFTP again and then think from there.
But the wiki has I think an error in the text here: