Bernina KL. 940 Service Manual page 38

RE-TENSIONING THE TOOTHED BELT
Loosen screws 169 slightly
-
Spring 1 70 draws the gearing into the correct position and thus produces the belt
tension
- Re-tighten both screws 1 69.
WARNING: When re-tensioning there must be no displacement of the teeth between belt
and drive wheel.