Revert to Original TP-Link Firmware TL-WR840N v4

I found a solution somewhere to revert to original TP-Link Firmware by using following command
{dd if=original_firmware.bin of=tp_recovery.bin bs=512 skip=1}
where "original_firmware.bin" is an upgrade bin file downloaded from tp-link website for TL-WR840N V4 (first upgrade)

That worked and my router's web interface looked original but MAC Address of WLAN interface became FF:FF:FF:FF:FF:FF and when I connected my phone to this router via WiFi my Phone's wifi started turning off and on automatically until I turned my router off.

I have 3 questions now

  1. Can I obtain original factory firmware (for tftp recovery) from internet
  2. Can I obtain Original factory firmware (for tftp recovery) from other router of same model and hardware version.
  3. Can I just change WLAN MAC Address of my router from FF:FF:FF:FF:FF:FF to that printed on device.

Mazhar Iqbal Karachi Pakistan