Brother RH-9820 Service Manual page 67

Adjusting the pressure of the needle bar gear block
Secure the needle bar gear nut (6), and then while pushing the needle bar gear block (5) with a force of 78.4 N,
tighten the screw (7).
NOTE:
If pressure is not applied, it will not be possible to adjust the turning center for the needle bar and looper
base, and this will cause problems with sewing such as skipped stitches.
RH-9820
6. ASSEMBLY
0791B
58