ab.1.3. Drag When Rotating Main Tuning Knob
Sometimes when turning the main tuning knob, it may be noticed that there is an
excessive amount of drag, or a periodic increase in the amount of force required to turn
the knob. Assuming that the problem is not in the LMO itself, here are a couple of things
to check.
One possible cause is that the circular dial is binding on the cable bundle that is located
towards the bottom left of the circular dial. The cable bundle is held in place with a
plastic cable clamp which may have loosened with time allowing the cable to shift
forward and rub against the back side of the dial. Replacing the cable clamp and/or
pushing the cable further back may eliminate the drag. Alternatively, moving the circular
dial forward slightly may allow the dial to clear the cables.
Another possible cause is that the circular dial has a slight amount of ‘wobble’ as
described in the following section. This can result in a change in the force required as
the main tuning knob is rotated if the circular dial is binding on the nylon follower that
operates the slide rule dial. The small tip of the follower should track the groove on the
back of the circular dial, but should not bottom out in the groove. Moving the circular dial
outward (toward the front panel) slightly may eliminate the drag. Moving the circular dial
outward too far can result in the nylon follower coming out of the groove in the back of
the circular dial altogether.
Servicing Procedures Page 73
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