Hello, I recently bought TL-WR841N v12 and i want to flash it with custom firmware but in every site i looked there is firmware only till version 11. And here i found that there is v12 but still no info and how to flash it. So can someone guide which version should i download and how to flash it? Also is it reversible ?
Looks like not.
8 MB RAM and 2MB Flash only. See similar question on the DD-WRT forum:
According to LEDE wiki, the TL-WR841N v12 has 4/32MB, not 2/8MB.
https://lede-project.org/toh/hwdata/tp-link/tp-link_tl-wr841n_v12
Looks like you are right. My bad; copied the info from ddwrt, should have read the boot-log better. The OP asked already in the custom build thread for the whole wr841/740 family. No answer there yet.
I found three files in download page (https://downloads.lede-project.org/releases/17.01-SNAPSHOT/targets/ar71xx/generic/)
tl-wr841-v12-squashfs-factory-eu.bin
tl-wr841-v12-squashfs-factory-us.bin
tl-wr841-v12-squashfs-factory.bin
Are these are the compiled files for my router and if is it safe to flash them via the original tp-link software like a update?
no success here ..
Error code: 18005
Upgrade unsuccessfully because the version of the upgraded file was incorrect. Please check the file name.
Rename the file to firmware.bin
The TP-Link update page checks the filename length.
already tried and get the same error
Looks like you should use the factory.bin file that corresponds to the model you have (ie, if it is made for the US, EU, or the International model).
You should be able to flash the firmware using the TFTP method. See here:
https://wiki.openwrt.org/toh/tp-link/tl-wr841nd#tftp_recovery_via_bootloader_for_v8_v9_v10_v11
Is it reversible? Yes, you should be able to flash the factory firmware from the TFTP recovery. Problem with that right now is, TP-Link hasn't published any updates for v12 yet. So, yo may have a hard time finding an original firmware to revert back.
Finally success 
I was needed EU version and needed to rename it to firmware.bin, only after this I was able to flash it.
BTW TP-link already published original firmware for v12 but i want to set up LEDE and test if for now.
Thank you all for the provided help.
firmware issues fixed but still having trouble .. is there any prob in old version?
What is the reason for the weak signal transmission 841v12