Symptoms: Xeno calibrate sometime, and failed sometime, sometime it bite the tongue after "try" to calibrate.
Root to the issue: loose lock bolt on the gear, casing the gear to spin on axle.
Fix: rotate the gear on the axle to so the flat area on the axle is under the umbraco bolt and tighten.
This was solved with help from Jesper Graver Jensen @ Sis Enterprise ApS (Retroarkaden.dk)