Problem binding XK K100 with iRangeX iRX-IR8M

I have an iRangeX iRX-IR8M transmitter which is working fine for my Bayang based quad and old walkera 4ch heli. I have recently bought an XK K100 Heli but I am having trouble binding. I have searched through the forums and followed all the advice including:
tried a couple of config files by other users.
reducing the power.
having a > 1 meter distance between transmitter and heli.
adjusting frequency fine and frequency course.
tried with channel 5 set to -100 and 100.

Has anyone had success binding an XK heli to the IR8M. My Tx is running deviation-ir8m-v5.0.0-b08efa8.

Any help/advice is appreciated.

Further update, I have tried the Heli with a friend's Jumper T8SG v2 plus which binds with the Heli fine, no issues. Performing the exact same steps with the IR8M does not work. I updated the IR8M to a nightly build last November, does anyone have the original V2 firmware? I couldn't;t see how to back that up when I flashed a newer one on.