Brother MFC-J3520 Service Manual page 265

If the internal ring is already set in the +1 or -1 position and cannot be turned
further, then replace the head/carriage unit.
Note: When turning the internal ring, hold down the head/carriage unit. Failure
to do so may cause missing block.

Turning the rings
External ring
Apply the tip of a flat screwdriver to the groove at section "A" shown in the figure
below. While pressing down the external ring with the screwdriver, turn it to the
+ or - position.
Internal ring
Insert the tip of a flat screwdriver under the external ring from section "B" and
remove the external ring upwards. Put the external ring on the internal ring
inside out and use it as a wrench to turn the internal ring to the + or - position.
3) Go back to step (2), print out a test pattern again, and check the D pattern.
Repeat this procedure until the number of block that shows the most indistinct
red color comes to be 2.
0
-7 +7
External ring
Internal ring
Fig. 4-1
A
B
Fig. 4-2
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