This is a notification for all owns Mercury MAC1200R V2.
The factory original uboot use RSA sign to check the firmware at the update time, and check flash at the boot time, so it is no way to install OpenWRT/LEDE to it.
Fortunately, I find the TP-Link WR841N has same architecture with Mercury MAC1200R V2, MT7628AN+MT7612EN.
So I download the TP-Link WR841N factory firmware, extract uboot from .bin and write uboot to FLASH with TTL.
After uboot replaced, everything is easy to control. Boot the router and press Reset for 10 seconds and uboot can automaticly fetch tp_recovery.bin from 192.168.0.66 and write it to FLASH.