Flash not possible tp link mr3020 v3.20


I tried to flash my tp link mr3020 v3.20 by the procedure openwrt
-by the tp-link interface it does not work
-then by tftpd (press the key, then power supply, ethernet cable) it does not work

  • there remains the serial link via a USB ttl in 3.3V (TX RX and GND connected)
    in Putty console I don't see "Autobooting in 1 seconds"
    I have the following error message:

error unable to open config file: /var/tmp/dconf/udhcpc.conf
RT305xESW: Link Status Changed
open DNS error: No such file or directory

I reset several, I tried all the official TP-link firmware
nothing works, have you ever encountered this problem?

thank you

Has anyone ever encountered this problem?