Getting OpenWrt (and ROOter) onto a Mikrotik RB922UAGS

Can't get OpenWRT onto MT RB922UAGS.

I have found the help pages -

I've tried all the tricks to get the TFTP working but no luck. I have used Mikrotik Netinstall (which installs new MT R-OS via TFTP) and that works ok, but I have had no luck with Tiny PXE server or TFTPD64... I used a Windows computer, disabled all but one interface, disabled firewall and virus protection etc but no luck...

Has anyone successfully got OpenWRT onto this RouterBoard please?